Zagalni understand

SCSI (Small Computer Interface) was founded in 1980. on the basis of the ANSIX3T9.2 industry standard (transformed to the X3T10 specification) for the unification of the standard interface (after naming SCSI-1). The speed of data transmission was equally low, it lay low due to rich factors and on average it became approximately 1 to 2 MB / s, but still it outweighed the largest speed of attachments (hard disks), which could provide a speed of no more than 625 Kb / s to FM stations coding. The main advantage of SCSI in front of the IDE interface is that SCSI is split as an interface for richly tasked and deployed on a richly complex operating systems, allowing one hour to reach a large number of outbuildings. SCSI has played a significant role in the development of information and calculation complexes, which require connection to various types of outbuildings. This interface has a wide range of features that can be connected, and itself:

• Hard disks - hard disks (DASD - Direct Access Storage Device)
• Streamers, accumulators on magnetic lines and other attachments for sequential access
• Magneto-optic storage devices, CD-ROM, CD-Recoder
• I/O attachments, such as scanners

These add-ons are connected to the computer through a special SCSI adapter, and the operating system takes access to them through the external drivers. Availability on the SCSI adapter board of the wet processor significantly reduces the load on the central processor for an hour of I / O operations. Tsya furnishing gives a great advantage when working in a merezhі, as well as for those who are insured for a rich coristuvachіv and rich task environments through those that change the hour of the client's access to the annex. In desktop systems (desktop computers), the CPU load is not critical for most programs and programs, prote when working with graphics (especially when working with computer animation) I/O operations will be transferred to the SCSI adapter.

SCSI Specifications

Today, there are a few SCSI specifications:

• SCSI-1: 8-bit data bus and synchronous data transfer rate of 5MB/s. Roz'em 25- or 50 contacts;
• SCSI-2 or Fast SCSI: increased bandwidth up to 10MB/s over 8-bit bus. Roz'em 50 contacts;
• Wide SCSI (Wide SCSI): increased bus width to 16. Transfer speed increased from 10MB/s to 20MB/s. Rose 68 or 80 pins (Single Connector)
• Ultra SCSI (Fast-20) / Ultra Wide SCSI or SCSI-3: Data transfer speed increased to 20MB/s on 8-bit bus and up to 40MB/s on 16-bit bus. SCSI-3 provides support for a large number of attachments (up to 15 per channel). Socket 50/68 - or 80 pins (Single Connector)
• Ultra2 SCSI (LVD): for a further increase in the speed of SCSI, a Low Voltage Differential (LVD) low-voltage differential bus is required, in which signals are transmitted one hour over two drota, but in different polarity. Because of this, the stability to the bus override is sharply increased, so we can increase the speed of data transmission over a 16-bit bus up to 80 Mb / s and increase the length of the interface cable up to 12 m! For a new implementation, use an Ultra2 SCSI adapter, an Ultra2 SCSI cable from an Ultra2 SCSI active terminator, and a drive that supports Ultra2 SCSI. Due to the presence of any overridden components, the Ultra2 SCSI standard automatically mimics and the system works in one of the forward SCSI specifications. Rose 68 or 80 pins (Single Connector)
• Ultra3 SCSI (Ultra160 SCSI): shvidkіst peredachі danih Mauger dosyagati 160 MB per second zavdyaki podvoєnіy sinhronіzatsії danih (danі peredayutsya vdvіchі shvidshe without zbіlshennya taktovoї frequency) polіpshenomu mehanіzmu optimіzatsії shvidkostі obmіnu danimi of rіznimi attach that vikoristannyu CRC algorithm zamіst control parnostі pіdvischennya nadіynostі peredachі . The specification for Ultra160 SCSI is the same as Ultra2 SCSI for cables, plugs and terminators. The Ultra160 SCSI controller can be simultaneously powered on one Ultra160 SCSI bus and Ultra2 SCSI add-on, moreover, it works at maximum speed. Rose 68 or 80 pins (Single Connector)
• Ultra160+ SCSI: a modification of Ultra160 SCSI, in which Packetized SCSI is implemented - a packet-based method of transferring information (commands, data and registers will be transmitted in one block with the same firmware) and Quick Arbitration Select (QAS) a method of quick arbitration select (QAS) As a result, the stutters are fast and the integral speed of data transmission is moving.

Basic SCSI interface implementations

· All disk drives and other SCSI attachments are connected one by one sequentially (in lantz) to establish a SCSI channel.

· Up to one SCSI channel can be connected only to SCSI attachments, as long as the same type of SCSI interface can be connected.

· On one SCSI channel, there are no faults for attachments that can have a single-ended (single-ended) (single-ended) (single-ended) interface and that can be a differential (dual-polar) interface.

· Up to one SCSI channel at a time can be connected up to a maximum of 8 for 8 bit (narrow - narrow) data bus or up to 16 for 16 bit (wide - wide) data bus SCSI attachments, including a SCSI controller. However, it is necessary to add additional facilities for the number of outbuildings that are connected to SCSI, depending on the input cable and data transfer security.

· The skin SCSI attachment, including the SCSI controller, is responsible for the mother's unique SCSI number (SCSI ID). Valid SCSI ID range: 0 to 7 for 8-bit (narrow) data bus or 0 to 15 for 16-bit (wide) data bus. All SCSI IDs are equal, however, on SCSI controllers, SCSI ID = 7 is installed and this number is not recommended to be assigned to other SCSI devices.

· Offending the end of the SCSI channel is due but completed with a special extension, whichever you need - a terminator (Terminator). The terminator can be located in the middle of the SCSI outbuilding, mounted on the end of the connecting SCSI cable or connecting panel (backplane) or in front of the external outbuilding, which is connected to the rest of the pink SCSI channel.

· All intermediate (not extreme) SCSI attachments may not be terminated. If there is a terminator on these SCSI devices, change the switch so that the "terminator enable - TE" jumper is near the "Off / Disable" position.

· The rear SCSI cable is subject to the ANSI X3T10/1142D standard (Section 6) for the following parameters:

Characteristic hvilovy opir

Hut RosesSunday

Sukupna dozhina

Admissible dozhina vіdgaluzhen

Interval between outbuildings

In order to satisfy the characteristic fluffy support, it is necessary to twist an unshielded flat cable or a round shielded cable from steam conductors (twisted pair ribbon cable). It is not allowed to twist a cable with different cable supports on one SCSI channel. It is also not recommended to block both shielding and non-shielding cables on the same SCSI channel overnight. It is especially important to implement the SCSI interface for the specifications of Ultra SCSI, Ultra2 SCSI and Ultra3 SCSI.

How long is the length of the SCSI cable acceptable?

1) The maximum length of a single-ended cable (single-ended) SCSI interface must be allowed for a certain number of factors. The table below shows the maximum cable length for various SCSI specifications and configurations:

Specification	Data transmission speed	Max. cable length	Max. at the annexes
Fast SCSI	10 MB/s	3 meters	8
Wide SCSI	20 MB/s	3 meters	16
Ultra SCSI (8 bit, Narrow)	20 MB/s	3 meters	5
Ultra SCSI (16 bit, Wide)	40 MB/s	3 meters	5
Ultra SCSI (8 bit, Narrow)	20 MB/s	1.5 meters	6-8
Ultra SCSI (16 bit, Wide)	40 MB/s	1.5 meters	6-8
Ultra2SCSI	80 MB/s	1.5 meters	16

Give respect: At the same time, the Ultra SCSI (narrow or wide) interface is theoretically responsible for trimming up to 8 narrow or 16 wide extensions, the X3T10 / 1071D specification does not allow adjusting the number of extensions for a variable cable. In order to connect more than 4 extensions, it is necessary to charge a special charge-backplane (backplane). But remember, the maximum speed of data transfer will be available only when connecting no more than 8 outbuildings. Dovzhina vіdgaluzhennya may buti no more than n_zh 0.1 meters.

2) The maximum length of the high-voltage differential (HVD - High Voltage Differential) SCSI interface cable is 25 meters. For a high-voltage differential SCSI interface, a twisted-pair cable is required. Dovzhina vіdgaluzhennya may buti no more than n_zh 0.2 meters. The interval between the outbuildings on the main SCSI bus is to blame, but the larger one is for a longer service life. Ale, regardless of the location, up to 16 SCSI attachments can be connected to the high-voltage differential SCSI interface, which can be addressed via a 16-bit SCSI bus.

3) Maximum cable length for low-voltage differential (LVD - Low Voltage Differential) SCSI interface - up to 25 meters for 2 extensions or up to 12 meters for larger lower 2 extensions. Others are similar to those of a high-voltage differential SCSI interface.

Can I change the type of SCSI interface to look like SCSI?

Unfortunately, I can only say about the SCSI interface: "Narrow" or "Wide". Below is a stark view from the side of the rear roses of some SCSI attachments:

Narrow attachment with SCSI-1, SCSI-2 or Ultra SCSI interface.

Wide attachment with SCSI-2, Ultra SCSI, Ultra2 SCSI or Ultra3 SCSI interface.

Wide SCA attachments with SCSI-2, Ultra SCSI, Ultra2 SCSI or Ultra3 SCSI interfaces.

Additional information can be found on the website of the manufacturer of the SCSI add-on model.

?"> What does mean?

The SCA interface is split to provide a standard connection for systems like hot swappable drives. Drives with an SCA interface are connected to a special SCSI backplane, which provides power supply, SCSI ID installation and SCSI bus termination. The distinguishing feature of drives with an SCA interface is an 80-pin rose, in a combination of interface roses, life roses and contacts for SCSI ID.

How to connect a floppy drive from SCA interface to SCSI controller with standard 50 or 68 visible SCSI interface?

To connect a drive with an SCA interface to a standard SCSI controller, a special SCA adapter is required. The SCA adapter is responsible for 50 or 68 pin interface roses, life roses, as well as the same on the drive, terminator and attachments for inserting SCSI ID.

Installations on the SCSI computer are not supported (not recognized). What is the reason?

Try next:

· Check that the SCSI controller is up to which SCSI device is connected, and it works correctly. This indicates that the BIOS of the SCSI controller has been captured after the system board BIOS has been captured (so the SCSI controller may have its own BIOS) and the notification of the successful capture of the SCSI controller drivers (for DOS) or for the Windows warning of the normal functioning of the SCSI controller (for the SCSI controller). For example, you can't change the installed port number, I/O address for the SCSI controller board, and the correct version of the drivers for this type of SCSI controller and operating system.

· Be sure that the SCSI cable and the live cable may be properly inserted.

· Be aware that all SCSI attachments can have different SCSI IDs. The SCSI ID for the SCSI attachment can be reserved for the SCSI controller.

· Make sure that the SCSI bus terminator is installed correctly: only on the outermost SCSI extensions is the lanyard and it is disabled (removed) on all intermediate SCSI lanyards.

· If a SCSI controller has its own BIOS, change the parameters for which SCSI controller is converted to SCSI attachments (data transfer speed, data bus, parity control) depending on the characteristics of SCSI attachments.

What is required for the computer to immediately boot from the SCSI drive.

To take advantage of a SCSI drive, it is necessary to overcome advancing minds:

· The motherboard is the fault of the mother BIOS, which allows the operation of the operating system with SCSI attachments. In this way, the presence of IDE disk drives is allowed. If the motherboard is old (the BIOS can only be used with SCSI attachments), all IDE drives can be disabled. In the extreme case, the presence of IDE drives is allowed, in which all the formats are distributed (Extended).

· The SCSI controller is the fault of the mother of the BIOS. Reconsider that in the parameters of the SCSI controller, in the section, the number of the type of SCSI attachment is set.

· Advanced partitioning of the SCSI drive can be formatted like (Primary) and (Active).

What do I need to implement the LVD SCSI interface?

For the normal functioning of the LVD SCSI interface, except for the standard SCSI interfaces (unique SCSI ID, SCSI bus termination) you need to use the following LVD-specific instructions:

· SCSI controller is responsible for LVD interface

· 3 both SCSI terminals languishing buti active LVD terminators

· all SCSI attachments on the bus line support LVD interface

Never-before-seen, we could make it so that a SCSI system could no longer function on larger SCSI specifications.

How many LVD attachments are summed from SCSI attachments to the front specifications?

LVD SCSI interface is completely summable from single-ended (single-ended) SCSI interface. Because of the unique features of the LVD SCSI interface, like multi-moding, a special input / output cascade circuit (DiffSens) automatically determines the type of SCSI bus, to which connected attachment (LVD or single-ended), it adapts to the bus's capabilities. That LVD add-on will work with SCSI-1 and SCSI-2 interface. First of all, SCSI-1 and SCSI-2 single-wire attachments work on LVD buses. Integrity - the specificity of SCSI is important, but if there are different SCSI attachments in different regions, they will be prepared on the same SCSI bus, all peripheral attachments on this bus will work on the same SCSI specification, so they will be attached to the same bus. For example, if a single-ended add-on is connected to the LVD bus with LVD add-ons, all add-ons on that bus will run in single-ended mode.

High Voltage Differential (HVD) add-ons require a special controller and cannot be combined with LVD or single-ended add-ons.

SCSI interface

On the cob of the 1970s for mini-EOM SCSI(read "tell"), naming what is deciphered as Small Computer System Interface. Well, I know, the name shows yoga "portability". The first variant transferred the data exchange rate of 5 Mb/s, and the extensions were connected to an additional 50-wire cable. Over the years, SCSI has had various additions and upgrades, increasing the speed of the exchange - today's SCSI controllers improve the speed of up to 160 Mb/s, which is larger, lower than the standard PCI bus. And the most important SCSI standard, zrozumіlo, has already become old and at the same time practically does not remember anything about it. SCSI options are rich, and all the stinks can be different and confused names (the situation is practically the same as with IDE), so it’s not clear to see the skin, but the main provisions are up to the table.

It's easy to improve the bandwidth: for which one you need just take the numerical value of the frequency, and for the Wide mode, multiply it by two. For example, an UltraSCSI controller (often referred to as Ultra SCSI-2) has a bandwidth of 20 Mb/s. These tables are already out of date, shards, it’s probably up to it, the maximum is 80 Mb / s (Ultra2 Wide SCSI, or just UltraWide SCSI, so Wide SCSI controllers are not allowed at once, not Ultra2, and Ultra can be abbreviated to Ultra2), and already it became very wide, it took off the speed of 160 Mb / s (this standard is called Ultra160 SCSI). These standards are only available with an LVD interface ( Low Voltage Differential), which ensures the improvement of the deficiencies and the increase in the allowable durability of the SCSI cable.

Axis type roses, which can be seen on SCSI controllers:

Internal
Low Density 50-pin	Connecting internal add-ons - old HDD, mayge all CD / DVD-ROM, CD-R, MODD, ZIP, etc. (like IDE, less than 50 contacts)
High Density 68-pin	Connection of internal wide-attachments, mainly HDD
Zovnishni
DB-25	Connection of the zvnіshnіkh vіlnih pristroїv, most importantly scannerіv, IOmega Zip Plus. Most extensions on Mac. (like a modem). Zastariv
Low Density 50-pin	Abo Centronics 50-pin. Call for connecting scanners, streamers, call SCSI-1 (the first variant of SCSI). Yak and SCSI-1 itself, already old
High Density 50-pin	Either Micro DB50 or Mini DB50. Standard external socket for connecting scanners, old CD-ROMs, old HDDs.
High Density 68-pin	Abo Micro DB68, Mini DB68. Standard external wide socket, mainly for HDD connection
High Density 68-pin	Similar to the front (practically nowhere zastosovuetsya)

There is also one type of rose - CL, otherwise Single Connector May 80 contacts. Single Connectors are used in the main host-swap (if you need a hot swap) configurations, so as to combine SCSI live and ground signals in one socket.

Krim vyschezgadanikh іnterfejsіv іsnuє sche so ranks Serial SCSI, which is based on technology fiber channel. Attachments are connected to the controller for an additional 6-core cable that can be wired at speeds of 100 Mb/s and more. On Serial SCSI controllers (also often referred to as SCSI-3), the primary roses are narrow and wide, which allow connection and standard SCSI attachments. Fiber Channel is a more predictable mesh standard, lower interface for connecting wearers; at the new victorious, there is a subsequent transmission of data. Report on Fiber Channel technology to marvel at the article Fiber Channel Technology.

For robots, I’ll build it, as it seems, I need a software support. For most IDE-attachments, it is entered into the BIOS of the motherboard, for others, drivers are required for different operating systems. SCSI-attachments have more folding. For the primary capture of a SCSI hard drive and working in DOS, you need your own SCSI BIOS. There are 3 options here:

• Chip zі SCSI BIOS є on the controller itself (like on video cards). When the computer is captured, it will be activated and allowed to be captured from a hard disk SCSI or, for example, CD-ROM, MO. Under the hour of a non-trivial operating system (Windows NT, OS/2, *nix) for robots with SCSI attachments, the drivers must be changed. Also, stinks are necessary for robotic attachments, like not hard disks, under DOS
• Image of the SCSI BIOS firmware of the Flash-BIOS of the motherboard. Change BIOS to add SCSI BIOS for controllers based on the most advanced chips. You can reflash and change the SCSI BIOS version to a new one yourself. For the presence on the motherboard of the SCSI controller, such a pidhid is won. This option is also economically viable - a controller without a BIOS chip is cheaper.
• SCSI BIOS doesn't light up. The work of all SCSI devices is provided only by operating system drivers. Zavantazhennya from them, obviously, is impossible. Such a change is made when a damp controller is set up for some kind of a well-known outbuilding (for example, a scanner), so if there is no sense in the outbuilding, and the victorious driver is transferred to a kind of outbuilding

Let's see how to get started with SCSI attachments, BIOS, turn on some more functions: adjusting the adapter configuration, rechecking surface disks, formatting at a low level, adjusting parameters in the initialization of the SCSI-attachment number, shutting down The SCSI BIOS often needs to be configured with SCSI devices. Tsyu role zazvychay vikonuє small microcircuit type 93C46 (flash). It connects to the main SCSI chip. May be only 8 small and a few dozen bytes of memory, prote її inmіst zvіgаєєє і і ​​nіnnіnіnі zhenennia (similar to CMOS on the motherboard). With this SCSI chip, the BIOS can save both the parameters of the SCSI devices and its own power settings. In a wild manner, the presence is not related to the presence of a microcircuit 3 SCSI BIOS, but, as practice shows, they should be installed at the same time.

Use also other controllers for servers. The cream of the language support for the most advanced modes of the stench can play support for RAID, hot disk replacement and an additional SCSI channel, which allows you to increase the number of attachments that can be connected. Often, a hardware cache as large as 32 megabytes, 64 or more is installed. For a little bit of evil, you can watch such a controller from the company ASUSTeK (good, to say the least, a company). On the yoga board, you can clearly see the 486 processor, which, perhaps, can be treated with all the good things.

Also, on the SCSI controller board, you can see the light-emitting diode of the SCSI-bus activity and/or sockets for this connection, and also the cache support, and other slots for memory modules. Buvaє, scho put dodatkovy IDE-controller, sound card or VGA-card. On some old controllers, you can sometimes find roses for connecting floppy disk drives.

Up to other no more than enough attachments (beep scanners), the kit often comes with its own SCSI controller. As a rule, the configuration can be simplified too: only redeem for one attachment and work with it, do not use the BIOS, work only with your own driver and without interrupting (polling mode). From the economic point of view, it’s completely true, for those who need to get a lot of opportunities (it’s reasonable to think that the most primitive SCSI option is shorter than LPT or USB) at minimum wages. Ale, from the other side, it’s not good, that’s nothing, the crime of your native annex is a 100% guarantee of winning. Although it is not necessary for anyone in particular - all the same, the speed of operation of such cards is small and with real consumption in SCSI it will happen to be more serious.

Attachments are connected to the controller with a narrow (narrow or wide) lanyard cable (similar to IDE). It is necessary to deal with the existing extensions, only here it is possible to draw an analogy with the last connections, say, a scanner and a printer to a parallel port. Do not give special respect to the swedish showcases of wear, to that in the most vipadkiv diє the rule: "If you rise up, it means you will practice." It is true that this time it is possible to upgrade robotic tires, to that, as it is possible, it is more likely to connect a more convenient extension up to one rose, and shvidki - up to another. Sure, controller I am guilty of disconnecting the connection of one cable I will add, to install a link with them. For which leather attachment can be your logical number, which one is called is called SCSI ID. For attachments on a narrow SCSI bus, you can enter 0 to 7; there is only one controller, and if it is narrow and wide, then there is only one SCSI bus, and all extensions on it have unique numbers. For some purposes, for example, at libraries of CD-ROM attachments, there is also a LUN - a logical extension number. If there are 8 CD-ROMs in the library, then there may be a SCSI ID, for example, 6, but logically a CD-ROM "and are separated by LUN. For the controller, everything looks like pairs of ID - LUN, in our case 6-0, 6- 1, ..., 6-7 You need to enable the LUN trim in the SCSI BIOS if necessary. parameters such as the type of parity re-verification (like the controller її pіdtrimuє), the inclusion of the terminator, the life of the terminator (div. distance), the inclusion of the disk after the controller's command, etc. Well, I know, often everything can be done in a programmatic way through the BIOS , which does not require a reboot For SCSI robots, it is enough for more than one reboot (for the controller itself), which, on the IDE view, allows you to save a resource and that gives you the ability to install more hardware into the system.

Now, as it was said, about terminators. How short, tse takі gizmos, yakі put on the ends of the tire. Meta stoppage of terminators - to ensure the improvement of equal signals, to change the fading and reshuffle. To say that the problems with the terminators are the most wide-ranging, but it is still respectful of everyone to work, they are not blameless. Skin SCSI-attachment can be upgraded or removed terminators. Vinyatok to install deaky scanners, in some cases, the termination of the tire is turned on forever, and those same attachments are made with a scraped tire. Terminator options:

• Internal. Sound present on hard disks; only one jumper can be switched on
• Automatic More SCSI controllers may be so. The stench themselves virishuyut, turn on him chi
• Looks like a stack of resistors, on some CD-ROMs and CD-Rs themselves. Vymikayutsya іdalennyam іz panels uѕіh sbіrok.
• Zovnishni. Like at the front point, but prettier (for example, on the HP T4e streamer). Attachment (sound the call) in this case may have two SCSI sockets: one plugs in the cable to the controller, in the other - the terminator or the cable to the step attachment to the lanyard.

You see, the two rest, it’s true, they’ve already grown old and don’t get stuck. In addition, terminators can be passive or active. Today, practically everything is active, the stench will provide greater stability to the transition and superiority on high windshields. You can choose which one to use on the SCSI add-on, you can sound for the way you turn it on. If there is only one jumper, or if it is automatic, then it is more active for everything. And as for yoga, it is necessary to pull in 1-2 resistor assemblies, then it is passive. In principle, terminating tires with different tires with different types of terminators is possible, but only on low tires. Before speech, there is one more argument for the greediness of the subdivision of those common outbuildings on various controllers and channels.

The report about the terminators is written in the description of the skin attachment. Termination rules are often labeled with the adapter's helper. It's smut to sound like this: the SCSI bus can be terminated on both ends. Let's take a look at the widest options for attachments in one SCSI bus.

The simplest option: the controller and one attachment (the names of the internal ones are not important). Terminators must be marked both on the controller and on the extension.

Option from a kіlkom vnutrishnіmi outbuildings. Terminator of inclusions is no longer on the rest of the annex and on the controller.

Іsnuyet like internal, so ovnishnі outbuildings. Terminators are included on the outermost and outer outbuildings, and left on the controller.

Є vnutrishne and kіlka ovnіshnіh outbuildings. The terminators are included on the internal and on the remaining outside building.

Trohi folded situation, if on one controller (tire) there are narrow-and wide-outbuildings at once. Let's assume that we have two 8-bit buses, which is really just the high and low byte of the wide-bus (in the descriptions of the SCSI BIOS it is called High byte/Low byte). Now, trying to make more rules, it is necessary to put a stop to insults on the bus. Sound at the time on the controller, you can independently terminate the high and low bytes of the wide-bus. In this situation, the narrow bus is the continuation of the young byte of the wide bus. We aim one example:

Narrow-attachment as a whole can be twisted and on a wide-bus navіt, if there is no necessary rose on the controller (both external and internal). You only need to use a wide-narrow adapter, or you can use a standard SCSI cable with a narrow-pin on one end of the wide-narrow on the other. Most often, this is the need to blame when connecting called narrow-attaches to a wide-controller; Likewise, you victorious adapters, give respect to the termination. When connecting a zvonishny narrow-attached to a wide-pin, the adapter is responsible for terminating the high byte. If narrow-attachment is connected to an internal rose wide, then the adapter simply transforms roses (to shorten the number of wires from 68 to 50). True, as it has already been planned, the termination is often carried out by the controller himself and by the outbuildings in automatic mode, and the problems are not to blame; cі vіdomostі navedenі more gladly like dovіdkov, аnіzh practical information.

At various conferences and FAQs, it is common to put food like "Which is shorter: IDE or SCSI?". The conclusions on the new arc are simple, but with a small and even more important addition: "Be surprised for what." Axis of the main SCSI over IDE:

High speed transmission

It is possible to work one-hour with usma outbuildings, de stinks would not be known and yak would not be connected

The length of the cable can be 3-6 meters

There is a greater height difference between IDE controllers and SCSI add-ons

Possibility of victorious outbuildings

The maximum number of attachments (up to 15) is significantly larger, lower for IDE, before that, you can install a sprinkling of SCSI controllers (call no more than four)

For all SCSI attachments, only one reboot is required

To increase reliability and swidcode, you can cheat cache, RAID technology and host-swap. True, in the last hour, similar IDE controllers began to appear, but stink, insanely, not the same garni as SCSI

However, for all its beauty, SCSI is an expensive interface. Prices are as inspectors, so are attachments. First of all, if you need SCSI, you need to be aware of the goals set. For a job, let's say, in Microsoft Office, we don't need high swidcode. Until then, the benefits are even less memorable in times of active richness of tasks. Also remember that for a small penny you can buy a larger swedcoded and smaller hard drive with an IDE interface, a lower one with SCSI. But if you are engaged in video editing, CD recording, folding graphics, or you just want the maximum code in your favorite Unreal" (otherwise you have a crush on it), then here is SCSI, of course, a lot of stained pennies. you are interrupted at the zhalyugidny camp, then virishuvat here especially and nothing.

	General information about interfaces……………………………………….
	Classification of interfaces………………………………………………
	History of the creation of the SCSI interface……………………………………
	The evolution of SCSI standards………………………………………………..
	What does a SCSI controller look like…………………….
	Concept of SCSI…………………………………………………………….
	Phases of the robotic SCSI bus…………………………………………………..
	SCSI Commands………………………………………………………………
	Host adapters………………………………………………………….
	SCSI cables……………………………………………………………...
	Software support for SCSI attachments……………………………...
	Programming of hardware accessories of peripheral devices.
	SCSI vs IDE……………………………………………………………
	References…………………………………………………………

1. General information about interfaces

The creation of modern technologies for calculating the number of equipment is due to the integration into one complex of various blocks of the EOM, the addition of the collection and display of information, the equipment of these and without intermediary EOM. The task is to entrust the unification of the system of obtaining - interface. Under the interface, it is possible to understand the sequence of circuitry, so as to ensure the interplay of storage elements of the calculation system. The interface provides for interfacing between storage functional blocks and system add-ons.

The main recognition of the interface is the unification of internal and intersystem links and extensions obtained with the method of effective implementation of progressive methods of designing functional elements of the computational system.

2. Classification of interfaces

1) Machine interfaces are recognized as organizing connections between warehouse elements of the EOM, tobto. without intermediary for them, induce that connection with the outer world.

2) Peripheral interfaces to determine the functions of obtaining processors, controllers, attachments, to remember, and data transmission equipment.

3) Interfaces of multi-processor systems - most importantly, backbone systems of obtaining, orienting at a single complex of multiple processors, memory modules, controllers, storing attachments, spaced-out accommodation.

4) The interfaces of the subdivisions of the AP are designated for the integration of the processing of information, placed on a significant area.

The development of interfaces is being directly promoted by the unification of the interface and the standardization of the minds of the totality, the modernization of the main interfaces, the creation of new interfaces.

3. History interface creation SCSI

The name of Shugart is known to be rich: it belongs to one of the most famous pioneers of the "accumulation" industry - the legendary silicon olympian (in the sensational bag, the Olympus of Silicon Valley) Alan F. Shugart, who is an IBM ker. In 1973, Shugart obtained capital from the side and created a company with the development of 5.25-inch FDD drives - Shugart Associates. Tsya firm propratsyuvala pіd yogo kerіvnitstvom rіk, after which Shugart was kicked out by those people who invested in the repair. Shugart was informed of the strike of six fates - during this period of wine he bought a fisherman's coat and became a professional fisherman. However, the craving for high-tech did not pass: in 1979, the company became the largest independent manufacturer of hard disk Seagate 1998 Shugart was “flooded”, but we already know the other story).

We are more likely to be called Shugart Associates, the shards of the same won in 1979, the company developed the SASI interface - the earliest variant of the SCSI bus. The abbreviation SASI can be spelled out at a given hour, the first two letters reliably mean Shugart Associates, the fourth - Interface, and the third in other words are deciphered differently - System, Systems or Standard (I think the correct version is the rest). The possibilities of SASI were more modest compared to the first variant of SCSI - the speed of transmission became less than 1.5 MB / s, the interface could be even more typing commands. However zakladenі in SASI іdeї carried in sobі bagato Progressive: zamіst povsyudno poshirenoї todі analogovoї poslіdovnoї peredachі vikoristovuvalasya 8 rozryadna parallel digital zamіst zv'yazuvannya lіnіy upravlіnnya іnterfeys slapped nabіr teams, that second pratsyuvav on logіchnomu rіvnі, dozvolyayuchi adresuvati blocks instead fіzichnі heads, cylinders and sectors.

Two years later, like 1981, in order to adopt the interface to the industry, Shugart Associates, after leaving the NCR (National Cash Register), filed an application with ANSI for the creation of a technical committee to further standardize that interface. Such a committee - X3T9.2 - was adopted in 1982, and the name of the interface was changed to a special SCSI description. Over the years, the standard has been upgraded and improved: the bandwidth has expanded, the command sets have been added - for printers, streamers, processors, WORM- and ROM-attachments. (It is necessary to note that SCSI on the SASI desktop has become not just a disk interface, but a kind of system bus: theoretically, on a “bare” SCSI, you can take a complete system by connecting a processor, memory, and accumulating peripherals.) Following the introduction of a black SCSI version y 1984 On the basis of ANSI, a lot of companies began to produce products, more or less summed up with the protostandard. The first official standard - X3.131-1986 - was adopted in 1986 (with the appearance of upcoming versions of yoga, they began to call SCSI-1).

The coming additions and the thorough developments led to the creation of the SCSI-2 specification.

4. The evolution of SCSI standards

SCSI specifications strictly define the physical and electrical parameters of the interface and the minimum number of commands. Zastosuvannya tsikh commands and became the main perevagoyu іnterfeys SCSI, oskolki zrobilo yogo keranovym. Expanded in 1985, the SCSI-1 specification introduced data transmission over a bus with a capacity of 8 bits and a frequency of 5 MHz. The speed of data transmission over the SCSI bus in the standard asynchronous mode (or handshake mode, so if it is necessary to confirm the data after the skin overstrength) becomes close to 3 Mb / s. When transmitting in synchronous mode, the SCSI bus can expand the throughput by about 5 Mbps.

Attachments were connected to the lancet one by one. The first one connected to the SCSI interface on the host computer, the other one - to the first one, etc. (div. Figure 1). First of all, the rest of the building was owed in the lansy, but they were terminated. On other outbuildings, the terminating was necessary to be turned on. Attachments were identified for additional jumpers (jumper) or jumper IDs (type 0 to 7), with which bus adapter on the host it was assigned, as a rule, ID=7, which gives the highest priority when accessing the bus.

Malyunok 1. Typical scheme for connecting SCSI attachments like a lance.

The standard did not goiter, but rather described the nature of contacts. The largest extensions are D-Ribbon type Centronics for PC and DB-25 for Macintosh. The terminology was more importantly passive, more active, or the regulation of the terminology was stagnant with only a few virobniks.

At the beginning of 1990, the SCSI-2 (Fast SCSI) specification was officially praised, and in 1990 it was officially praised, which defines 18 basic SCSI commands (Common Command Set, CCS), binding languages ​​to all peripheral devices, and adding additional commands for CD. - ROM and other peripherals. It became possible to exchange data without the participation of the central processor. "Chergs" appeared - the ability to accept lancers up to 256 commands and process them autonomously in an optimized order. And if the controller of the viconic attachment-addressee has removed the command, if it does not see any calling interactions, then this controller will not occupy the bus until the need for transmission appears. Here you can seriously override SCSI over IDE, especially in multitasking environments: the IDE bus works as a passive channel for transmitting signals to the central processor - you can skip one command before initiating another.

Also z'appeared expanded spektіkatsії, znachennya yay often can be found in the price lists. The basic 8-bit version is Fast SCSI (SCSI-2) - the bandwidth is 10 Mb/s. Modification of Wide SCSI-2 with a 16-bit version of Fast SCSI (SCSI-2) and data transmission flexibility, and also allows connection of up to 15 peripheral devices. The prefix Ultra means the operating frequency has been shifted up to 20 MHz, and the Ultra2 controllers transmit data at a frequency of 40 MHz. The most common indications are Ultra Wide and Ultra2 Wide. Tse means that there are combinations of options. So, for example, Ultra2 Wide extensions can exchange information with a maximum speed of 80 Mb / s.

The Ultra160/m SCSI specification was adopted on September 14, 1998. The main components of Ultra160/m SCSI were: Double Transition Clocking, Data Integrity Control with the help of CRC, Domain Validation. Transmission speed of 160 Mb/s is available with the help of both sides of the power supply/acknowledgment signal for data synchronization. Vіdpovіdno, tse dozvolyaє rozrobnikam zbіlshiti shvidkodіyu abo nadіynіst, oskіlki staє mozhlivim vikoristovuvati Smuga transmission shini to 160 Mb / s of іsnuyuchimi z'єdnuvalnimi Ultra2 SCSI cables abo pіdvischiti nadіynіst іnterfeysu Ultra2 SCSI (80 MB / s) zavdyaki znizhennyu frequency at yakіy vіdbuvaєtsya sinhronіzatsіya .

In order to control the data integrity for the cyclic code overriding (CRC) calculation, the Ultra160/m uses the same method that is used in FDDI, in local networks based on the CSMA-CD protocol and in fiber-optic data transmission channels. The control is sharpened by intelligent technology, which is used in the conversion of data collection subsystems, including return cables, terminators, etc. Tsya technology to control the functioning of the system in the necessary specifications, and if necessary, the need to spend data to reduce the speed of transmission.

According to the method of communication with the SCSI controller, the SCSI attachment is divided into two types: one single-ended and one differential (differential, D) electrical interface. In the single-ended interface, there is one conductor for the skin discharge of data or other signaling signals and a conductor for the "ground", and the information is transmitted only over one signal conductor. At the differential interface, the signal is subdivided into positive and negative storage and is transmitted over a pair of conductors, which allows the signal to be transmitted over long distances without reshuffles. Selecting the type of SCSI transceiver determines the maximum bus life and the number of attachments that are connected. Most of the main SCSI add-ons use single-ended transceivers, which can lead to a change in cable life with an increase in transmission speed. Differential transiveries do the same thing, but they are rich. The solution to this problem is the Low-Voltage Differential (LVD) technology, which is a hybrid of two vital technologies. Most of the new additions are introducing universal transceivers, which can be used as single-ended and LVD transceivers.

Discharge,

Maximum transmission speed, Mb/s

Maximum cable length/number of extensions, m/piece

Number of contacts at roses

6/7.25/6(0), 12/6 (LVD)

3/7.25/6(0), 12/6 (LVD)

Fast SCSI-2, Fast SCSI

3/15.25/15(0), 12/15 (LVD)

3/3.1.5/7.25/6(D),12/6(LVD)

Wide Ultra SCSI-2

3/3.1.5/7.25/15(D), 12/15(LVD)

Fast-20 Wide SCSI

Wide Ultra2 SCSI-2

Fast-40 Wide SCSI

Ultra3 Wide SCSI

There is also an 80-pin socket for connecting attachments in Hot Swap mode. The peculiarity of such a rose is the presence of contacts in the life order with contacts for the transmission of data and essential signals.

5. What does the SCSI controller look like?

Axis of the picture of the simplest FastSCSI controller on the PCI bus.

As you can see, most of the space is occupied by roses. The largest (and oldest) price for 8-bit internal outbuildings, often titles narrow, Vіn similar to the IDE rosette, only in the new not 40, but 50 contacts. At the top of the controllers, there are even more modern roses, as if you are crying out from the name, you can also connect the outer SCSI add-ons as required. The image shows mini-sub D type roses for 50 contacts.

For Wide, a similar one is attached, but for 68 contacts, it is also fastened not at the clasps, but on the screws - like a COM bear and a printer. Vіn navit smaller, nizh narrow, for rahunok more high width of contacts. (Before the speech, regardless of the name, the wide train is narrower, lower narrow). Sometimes you can use the old version of the old rose - just centronix. Such a (calling, but not functional:) You can use your own printer. Add-on devices, for example IOmega ZIP Plus, as well as insurance on a Mac with a great 25-pin Cannon (D-SUB), like on a modem. For zovnіshnіh vysokoshvidkіsnіh z'єєdnаn zastosovuєtsya and minі-tsentry. Axis on the table:

(Expand mayzhe original)

Internal

Low Density 50-pin

connection of internal narrow attachments - HDD, CD-ROM, CD-R, MO, ZIP. (like IDE, less than 50 contacts)

High Density 68-pin

connection of internal wide extensions, mainly HDD

Zovnishni

connection of the outbuildings, most importantly scanners, IOmega Zip Plus. widest on Mac. (like a modem)

Low Density 50-pin

or Centronics 50-pin. new connections for scanners, streamers. Ring SCSI-1.

High Density 50-pin

or Micro DB50, Mini DB50. standard zvnіshnіy narrow roses

High Density 68-pin

or Micro DB68, Mini DB68. standard standard wide rose

High Density 68-pin

or Micro Centronics. for deakiemi dzherelami zastosovuetsya for zvnіshny podklyuchennya SCSI extensions.

For robots, I’ll build it, as it seems, I need a software support. For most add-ons, IDE is minimally installed in the BIOS of the motherboard, for other necessary drivers for different operating systems. SCSI add-ons have a lot more storage. For the primary capture of a SCSI hard disk and work in DOS, you need your own SCSI BIOS. There are 3 options here.

1. SCSI BIOS chip on the controller itself (like on VGA cards). When the computer is captured, the VIN is activated and allowed to be captured from a SCSI hard disk or, for example, CDROM, MO. Under the hour of a non-trivial operating system (Windows NT, OS/2, *nix) for robots with SCSI attachments, the drivers must be changed. So stinks of the necessary robotic attachments, like hard disks, DOS.

2. SCSI BIOS image of the flash BIOS of the motherboard. Dali for item 1. Go to BIOS and add SCSI BIOS for controller based on NCR 810 chip, Symbios Logic SYM53C810 (on the first picture) or Adaptec 78xx. By this process, you can repair and change the SCSI BIOS version to the new one. For the presence on the motherboard of the SCSI controller, there is such a pidhid. This option is also economically viable :) - a controller without a BIOS chip is cheaper.

3. SCSI BIOS doesn't light up. The work of all SCSI attachments is provided only by operating system drivers.

SCSI add-on recovery cream, BIOS turn on as many functions as possible: adjusting the adapter configuration, rewiring surface disks, formatting at a low level, adjusting the parameters in the initialization of the SCSI add-on number, managing the factory

The next step is respect. Yak Wee know, sing, on motherboards є CMOS. In the new BIOS, it saves the payment adjustment, the configuration of the hard disks. For the SCSI BIOS, it is often necessary to save the SCSI device configuration. Tsyu role zazvychay vikonuє small microcircuit type 93C46 (flash). It connects to the main SCSI chip. There may be 8 small and a few dozen bytes of memory; With this SCSI BIOS chip, you can save the SCSI settings of the device and its own controls. In a wild manner, the presence is not related to the presence of a microcircuit 3 SCSI BIOS, but, as practice shows, they should be installed at the same time.

Here you can download the ASUSTeK UltraWide SCSI controller. The new one already has a SCSI BIOS chip. You can also look at the inner and outer Wide roses.

On the rest (I couldn't know more) pictures of the two-channel Ultra Wide SCSI controller. This specification includes the following items: RAID equals 0,1,3,5; Failure Drive Rebuilding; Hot Swap and on-line Rebuilding; cache memory 2, 4, 8, 16, 32 Mb; Flash EEPROM for SCSI BIOS. Even better you can see the 486 processor, which, maybe, and is smeared with all the good things.

More information on the SCSI controller board can be

• activity LED of SCSI bus and/or sockets for yogo connection
• roses for memory modules
• floppy disk controller (important on older Adaptec boards)
• IDE controller
• sound card (on ASUSTeK cards for MediaBus)
• VGA card

Other SCSI cards

Often, a simple SCSI controller is added to scanners and other non-standard SCSI attachments. Switch on the SCSI-1 controller on the ISA 16 bus or send 8 bits with one (external or internal) socket. On a new one, there is no BIOS, eeprom, often works without interruption (polling mode), sometimes only one (and not 7) attachments. You can win such a controller only with your own attachment, tk. the driver is less than youma. However, for the singing novice, you can connect to a new one, for example, a hard disk or a streamer. It’s true that it’s more true for times of daytime pennies and the presence of an hour (abo for sports interest:), tk. A standard SCSI controller, as already mentioned, can be purchased for $20-40 and has an order of magnitude fewer problems and a lot more opportunities.

6. Concept SCSI

The SCSI bus is an I/O bus, not a system bus or a device interface. Interfaces to the SCSI bus type are especially effective for machines that require the connection of a number of disk storage devices to other PUs. The SCSI interface increases the flexibility and computational complexity of the system, the shards allow you to connect up to one bus of different PUs, which can be interchangeably interchanged one by one. The speed of transmission over the bus is insanely nothing to be judged by an intermediate official, but this indicator for the SCSI bus is 40 MB / s.

The SCSI bus transmits the possibility of connecting up to eight extensions. At first glance, it can be possible to achieve serious exchanges, prote, as if to lie, that skin attachments can represent all logical blocks, and skin logical blocks - 256 logical subblocks, it is obvious that the possibility of expansion here is more or less sufficient.

The skin from the SCSI bus attachments is responsible for assigning an individual ID, the value of which is set for additional switching jumpers directly at the attachment. Identifier ID has two functions: Identification of attachments on the bus and assigning priority in arbitration for access to the bus (whichever number I add, it is the highest priority).

Leather from eight possible extensions of the tire can play the role of an initiator (initiator), vikonavtsya (target), or reduce the offensive role. Initiator - part of the SCSI host (head) adapter, which serves to connect the host computer to the SCSI bus. In a typical system of one initiator, one or more victors are connected. The foldable system can accommodate more than one SCSI host adapter (many initiators). In such systems, it can be installed as an interoperability like a processor with a PU, or a host - adapters with each other, shards of a host - an adapter itself - we will add a SCSI bus and can play the role of an initiator, and viconate. Two PUs (offended vikonavtsі), prote, which are impossible to interact with each other, shards are only a couple of initiators - vikonavtsy can exchange money on the bus at the skin specific hour.

Host - adapter to host hardware and software for connecting to the CPU.

The interface of the SCSI controller and the system bus can be more simple (it will be based on the principle of software-based I / O channel), so more collapsible (which transfers high-speed data exchange in direct memory access mode, DMA). Such controllers accept high-level commands and call the CPU as needed for processing and monitoring SCSI bus signals.

The software security of a computer is easy to understand, but it is not possible to check the physical characteristics of a particular device. The SCSI interface transmits a logical rather than a physical address for all data blocks.

7. Phase robotic tires SCSI

SCSI bus protocol transmitting in four phases:

Bus Free - "Bus free"

Arbitration - "Arbitrage"

Selection - "Vibrka"

Reselection - "Zvorotnya vibrka"

Command - "Team"

Data - "Dani"

Status - "Stan"

Message - "Information"

The rest of the phases are called transmission phases. The SCSI bus at any given time may run over one of the eight phases.

The "Bus not available" phase means that the connection is currently not working with the SCSI bus in active mode, and the bus is not available for use. Tsya phase sound vikaє after the system reset or bus reset by the RST signal. The sign of the "Bus free" phase is the presence of busy signals BSY and the selection SEL.

The bus switches to the phase - "Arbitration", if you want to take control of the bus as a SCSI attachment, then become an initiator on the bus. Tse vydbuvaєtsya in vipadkah, if the initiator wants to choose vikonavtsya or vikonavets want to re-select the initiator, which he asked earlier. In the “Arbitration” phase, the bus can only switch from the “Bus free” phase. After the fact that the attachment indicates that the tire is free, the Arbitration phase begins. For whom the BSY signal is formed on the secondary data line

you can see the SCSI ID identifier - extension (ID - bit). With what skin

of the eight possible SCSI bus attachments you can see your ID-bit

I’m more likely to attach a line of data to him as a sign of my fate

in arbitration. Attachment with the maximum value of the ID will win arbitration and clear the bus.

The "Check" phase gives the initiator the ability to choose a win to initiate a win function, such as a READ read command or a READ write command. Depending on the SCSI-2 specification protocol, the "Vibration" phase will always start after the "Arbitration" phase. At the SCSI-1 specification, a system variant with one initiator is transferred, which requires arbitration every day, and the sampling phase can be included immediately after the “Bus is free” phase. In both options for dialing, the initiator sees an ID bit on the SCSI bus data line and generates the SEL dialing signal.

The neobov'yazkova phase of the re-election is possible, if you want to make a call from this initiator, who earlier sent you a team. This phase, in principle, predicts the “Vibirka” phase, with this vinjat, that at the same time, from the signal of the SEL vibrator, go to the active I / O line, which allows the two phases to be separated.

Phases "Command", "Daniel", "Stand" and "Information" establish a group of phases for transmitting information, shards of all stinks are selected for transmitting data or certain information on the data bus. In order to distinguish between them, the signals C / D - control, I / O - input-output and MSG - support, which are vibrated by viconators, are vibrated, which, by itself, involves all transitions from one phase to another. To control the transfer of data between the contributor and the initiator at the phases of the transfer of information, the signals of the REQ / ACK line - request / confirmation (in the SCSI-2 version, the REQB / ACKB lines are added additionally).

The real exchange of data can be done in a synchronous and asynchronous way. Both ACK and REQ signal lines are used in both rounds for rounding off. For vykonavtsya synchronous transmission mode є neobov'yazkovim. The initiator can make a difference in order to start the synchronous transmission, while the rest of the input is powered up, and the asynchronous mode is enabled.

To transfer data to the initiator in an asynchronous mode, you can use both SCSI bus data lines together with the REQ signal. The acknowledgment signal will not be received on the bus, the docks from the initiator will not accept the ACK signal. If so, such data is seen on the bus, and it is repeated. If the transfer of data can be sent directly to the other person, you will see a signal for the request REQ, which is to say about those who are ready to receive the data. The initiator sees data on the data line of the SCSI bus, and then generates an ACK signal. The initiator continues to reduce data on the dot bus, the REQ do not switch to the passive stance. Then the victor drops the REQ signal, the initiator sees new data and the process is repeated.

If at the “Awareness” phase the add-on had time to win the synchronous exchange mode, then it would not check for the ACK signal in front of the REQ signal to receive the upcoming data. You can generate one or more REQ pulses without scoring the second ACK pulses (up to the limit of the maximum, which is called the REQ/ACK offset).

When you see all the planned REQ impulses, you will increase the number of REQ drinks and ACK confirmation, in order to improve the skin group of those who have been successfully accepted. Before the hour of preparing the synchronous exchange mode, I will set the REQ / ACK offset for that transmission period. The transfer period defines the interval between the end of the transfer of the black byte and the beginning of the transfer of the forward byte.

8. SCSI commands

Forward specifications of interfaces for hard disks (as already ESDI guesses) passed the last transfer one bit at a time, with which the disk was reversed behind the last wires (lines), the skins of which lost the first function. For example, one specific signal line set the read/write heads of the hard drive, another one - the direct offset, the third - the type of operation (read or write), the fourth served to transfer data to the required format. In such a rank, controller, you win, lying in the form of a hard disk.

SCSI building vykonuvat vysokorivnevi commands, for example, ask the type connected to the bus I will add for the help of the Inquiry command. Thus, for the specifics of the physical characteristics of the tire (type of contact, voltage level, recognition of contacts, etc.) the standard for skin type peripherals (hard disk, CD-ROM, etc.) determines the commands that are vіdpovіdnі їm vіdpovіdі (about 12 skin types of the periphery). The standard SCSI-1 commands are grouped by up to six types of attachments, as shown in Table 1.

Table 1. Groups of commands depending on the types of attachments that are supported.

Attachment type

Name

Typical function

Vipadkovy read/write access (hard disk)

Addresses of logical blocks, the length of the recorded block

Last Access

Reading an offensive note

Side layout control

Processor

Directed by the reception

WORM (recordable CD-ROM)

Great rosemir, winter

Vipadkovy access is less for reading

Addresses of logical blocks, length of the read block

When zapіnі tsіl'ovіm pristroєm kommand, yak pri іnіtі zі zіrnennyam pc to the disk, іnіtіator vіdpovіdaє nadsilannym 6 byte komandіnformatsiї. Qi bytes serve as a command and identification addendum. All of them are called a Command Descriptor Block (CDB). The first byte (more precisely, byte number 0) determines the type of the command, which is the opcode. Deyakі the most wide code and may have the following meaning (for the sixteenth tax):

00 Test attachment ready;

03 Formatting;

08 Reading;

0A Write;

0B Poshuk.

The value of the bytes that are left out should be stored as a specific operational code. For example, at the time of the Write command (code 0A), the stink might be like this:

Byte 0 Operation code 0A;

Byte 1 Number of the logical device in bits 5 and 6,

bits 1 to 4 set the address of the logical block;

Byte 2 Logic block address;

Byte 3 Logic block address;

Byte 4 Bits from 2 to 5 set the transmission length;

Byte 5 Bit 1 - Ensign; bits 6 and 7 are assigned by the picker.

Sending commands is disabled in asynchronous mode. However, in order to remove data, the stench can be transmitted in synchronous mode, as in the case of the Inquiry command, in the case of a valid extension, the ASCII type is transmitted, which identifies this type (this type is often displayed on the PC monitor when running SC).

9. Host adapters

The host adapter implements the function of obtaining the SCSI bus from system resources, forwarding it from the system bus and the operating system of the computer. Vin, as a rule, wins the role of the initiator on the SCSI bus, although in folding (for example, in multiprocessor and multimachine) SCSI systems, it can dynamically change (initiator/winner).

Before the main functions of the host adapter, which determine its structure and characteristics, set:

Implementation of the SCSI bus protocol, as well as physical and electrical specifications of the standard;

Obtained from hardware and software system resources

The implementation of the SCSI bus protocol, as a rule, depends on a specialized BIS of the SCSI bus controller. Sound the scheme to ensure the implementation of electrical specifications to the standard.

Using the hardware system tools to transfer us to the bandwidth and throughput of the SCSI bus and the system bus of the host system, as well as the implementation of the various features of access to the system memory. The structure of the node to fit the width of the tires should be based on the recognition of the host adapter and the version of the SCSI standard (8 bits for SCSI-1; 16 or 32 bits for SCSI-2). The main way to improve the throughput capacity of the system and SCSI buses is buffer memory, which is implemented by sounding like a FIFO buffer, or dual-port RAM. The largest extension of the algorithm for accessing system memory is direct access, which is most often implemented behind the help of the PDP controller of the host system.

When software systems transmit the presence of a SCSI driver for a particular OS.

Characteristics of current host adapters

The middle of the selection of BIS SCSI controllers for the AT bus dominated by the NCR model. Followed by WD33C93 from Western Digital and ALC 6250/60 from Adaptec (USA). The host adapter most often supports both synchronous and asynchronous exchange modes via the SCSI bus. The speed of the exchange is deposited according to the type of vicorous controller. For simple host adapters, it can run from 0.25 to 1 MB/s in both asynchronous and synchronous modes.

The size of the data buffer also varies within wide ranges: in different internal buffers of the BIS SCSI controller of small capacity up to RAM with a significant capacity (1 MB). The presence of a great buffer significantly increases the variability of the host adapter.

10. SCSI cables

For the sake of insensitivity to shifts, the SCSI cables are not only twisted, but also arranged around three concentric balls (div. baby 2). The central, inner ball makes three bets: Request (“Request”), Acknowledge (“Confirmation”) and Ground (“Earth”). Middle - middle - ball to serve as transmission of important signals. The third one is the best one – the ball of appointments for the transfer of data and information about the couple. At the middle ball, the bet is twisted in a straight line with the outer and inner balls, which adjoin to the new one, for changing the double link between the balls. The location of the wires for the transmission of signals to control, in the middle ball, ensures the daily interference between data and Request/Acknowledge signals.

Figure 2. External SCSI cable at the outlet.

If you want the entire cable to be insulated with an additional polyvinylchloride coating, such insulation is not suitable for a few pairs, because the electrical characteristics strongly depend on the temperature, and in addition, there may be even more great єmnіst. Such a design of the cable is marked with a zreshtoy on yoga price. However, we are not so rich as to buy cheap speech.

11. Program support SCSI outbuildings

Programming manager of SCSI systems and add-ons and accessories and can be divided into such visually independent tasks:

Programming of hardware accessories of peripheral devices

Implementation of SCSI bus protocols.

Implementation of SCSI commands.

Access to SCSI OS and Application Tasks.

A lot of reputable firms promote their original, proteo often do not stick one with one approach. Vrahovyuchi, scho in the field of programming SCSI pristroїv the standard is actually not yet good enough, to take a look at the most common solutions for skin care.

12. Programming of hardware devices of peripheral devices

Kіntsevoy lankou zaobіv software pіdtrimki PU due to the specificity of physical principіnі v realіzаtsії inevitably є vuzkospetsіalіzovanі programs of low level. Through those that programming on such a level is easy to build for general system, but about applied programmers, there is a tendency to increase the level of programming of PU for the account of masking the specifics of PU on the level of the so-called firmware (internal software security - VPO). The butt can mask the functions of direct control of disk storage devices only on the basis of internal commands of disk controllers WD2010,8272 and others.

Prote on the river of registers of controllers there are only specialized programs. None of the PUs sound more like programmed on the same system BIOS functions, and the programs of the higher level rely on the standard OS functions.

The choice of the SCSI interface further advances the programming level of the PU with the additional help of the standard to the set of commands in a bold form. For an application programmer, using standard BIOS functions becomes practically impossible.

However, as an element of management of outbuildings, naturally,

are saved less on the level of HPE of the PU controller and are implemented either by the local microprocessor (MP) of the controller, or by the microcontroller, which is built into the base BIS of the PU controller.

In order to conserve programmatic functions for managing the electronics of the PU, in this hour, the emulation of standard PU interfaces is widely used, which transfers the transformation of the logical SCSI address to the physical address of a specific add-on. The butt can be a SmartConnex / ISA controller from Distributed Processing E Technology. Winning the interface of the Western Digital WD1003 disk controller, as a result, the computer "boots" the controller as a great attachment, combined with the ST-506 interface.

In reality, the interface is emulated by an invisible driver for the driver, which is remembered when formatted in the rest of the NMD block. Vіdpovіdnі є vіdnі vіdnі vіdnі є є vіdopіrіnіshih OS

(MS-DOS, OS/2, Xenix/Unix, Novell NetWare). The installation of the SmartConnex controller in the system is required for the help of a special utility company, which is supplied.

For other controllers WD 33C92/93 by Western Digital, the command to change formats to logical addresses from physical ones has been introduced.

In this way, for the implementation of various PUs, the SCSI standard can

there are fragments of ready-made programs that support such standard functions of the PU in MS-DOS, such as INT 13, INT 11 and in.

It should be noted that such a pidhid, perhaps, does not completely support the SCSI ideology, and in the future, special programs for the direct control of SCSI attachments based on SCSI commands will be victorious.

13. SCSI vs. IDE

Supertechka "Which is better: IDE or SCSI" to enter the widest range of teleconferences. The number of reviewed articles on this topic is even greater. However, the power, like the famous "Windows NT or OS/2 or Unix", is inseparable from such a setting. The most common and correct reaction is "And now?". Having looked at the main report, you can make a decision about the need for SCSI yourself.

Let's talk about how you can give a simple SCSI controller in a pair of IDEs and for which you need to choose or not.

SCSI proposition

EIDE/ATAPI listing

SCSI verification

Possibility to connect 7 extensions to one controller (up to Wide - 15)

it doesn't matter, install 4 IDE controllers and a total of 8 add-ons

on the skin of the IDE controller it is necessary to interrupt! І over 2 will be UDMA/33. A 4 UWSCSI ce 60 outbuildings :)

a wide range of attachments that can be connected

to IDE є CDD, ZIP, MO, CD-R, CD-RW

and the driver and software for everything you have exactly є? i rich? and the axis for SCSI can be twisted whether or not, including those that enter the OS warehouse

the possibility of connecting both internal and external outbuildings

Removable rack or LPT-IDE

The cable length of the SCSI cable can reach 25 meters. For the most prominent falls 3-6m *

if you do not open the PCI bus, you can і per meter

it is possible to use cache and RAID technologies for a cardinal increase in productivity and reliability

earlier, Tekram cached, and at the same time appeared and RAID for IDE

tse do not practice and vzagali not seriously

* Please note that the difference between the Ultra and Ultra Wide SCSI interfaces on the quality of the connecting cables and their duration is superimposed by additional connections, after which the maximum duration of the connection can be significantly reduced.

So that there is no hostility, that the IDE is even worse and for some reason you can be ashamed, significant and positive to the IDE interface, often in the light of the above table:

1. Price. Without a word, sometimes more respectfully.

2. Not everyone needs to connect 4 HDDs and 3 CDDs. Often, two IDE channels are more than enough, and all scanners go there with their own cards.

3. At the case of the minitower, it is easy to twist the loop, which has reached over 80 cm :)

4. Installing IDE HD is much easier, there is only one jumper, not 4-16 on SCSI :)

5. IDE controller already has more motherboards

6. IDE add-ons have a bus of 16 bits and for models that are equal for the price, IDE wins for the speed.

Now about the price. The simplest SCSI on the ISA bus costs about $20, but at the same time it's just not needed by anyone, so you can know it's cheaper. The next option is the controller on the PCI bus. The simplest FastSCSI option costs around $40. However, at the same time, there were no number of motherboards, on which for as little as $70 you can install Adaptec 7880 UltraWideSCSI. See ASUS P55T2P4 and P2L97 for SCSI options. For UWSCSI cards, the price varies from $100 to $600. There are also dual-channel (like IDE Intel Triton HX/VX/TX) controllers. The price of them is natural. Respectfully, what is the SCSI port, the IDE port, where it is easy to find a new way, for additional pennies, the controllers can be expanded with the functions of the cache controller, RAID-0..5, hotswap, etc., we can talk about the upper boundary controller is not correct.

І areshti about swidkіst. As you know, today the maximum speed of transmission on the IDE bus is 33Mb/s. For UWSCSI, the analogous parameter is 40Mb/s. The main advantages of SCSI are shown when working in multitasking environments (the one in Windows95 is not good :). A lot of tests, pointing under WindowsNT, show an unparalleled SCSI pass. Perhaps, the most popular on today's OS, for which the SCSI crowd is more true. Also, there can be specific tasks (for example, with a sample video) for those who simply cannot use the IDE. About vіdmіnnostі vіdmіnnostі vnutrіshnіh arhіkturov, scho kozh vplyvayut on proizvoditeln_n_n_nі, tsіy statti does not speakmemo, there are too many special terms. It is significant only, that after the development of the IDE, it is worth mentioning that the wines are rich in SCSI rice, but, spodіvatimemosya, nevertheless, we should not stink.

List of references

1. Mikhailo Guk: PC interface. Dovіdnik "Pіter", 1999.

2. A.P. P'yatibrativ:

"Counting machines, systems and measures"

3. A.A. Myachiv, V.M. Stepanov:

"Personal EOM and microEOM"

M .: "Radio that zv'yazok", 1998.

4. A.A. M'yachiv:

"IBM PC interface", 1992.

5. Stefan Feutz: "Windows 98 for Koristuvach"

K .: Trade and display bureau BHV, 1998;

6. PC Computing: IDE vs SCSI

7. "PC Magazine": "Interface IDE"

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The SCSI interface was developed in the style of the 1970s. orga-^ “Nizatsiya Shugart Associates. Back to top

under the name SASI (Shugart Associates System Interface), after standardization in 1986. vzhe pіd іm'yam SCSI (read "skazy") becoming one of the industry standards for connecting peripheral devices - hard drives, streamers, hard drives and magneto-optical disks, scanners, CD-ROMs and CD-Rs, DVD-ROMs. Up to eight add-ons can be connected to the SCSI bus, including the main controller

SCSI (or host adapter). The SCSI controller is, in fact, an independent processor and has its own BIOS power (as it may be located in the motherboard BIOS). Vіn vykonu є all opsії s s service and maintenance of the SCSI bus, which depends on the central processor. Up to 15 extensions can be connected to the Wide SCSI bus. The SCSI advantage is manifested only if a sprat of attachments is used at the same time with one bus, if it is not needed.

SCSI command protocol. In addition to other hardware implementations, the SCSI standard also includes a concatenation of commands, which, being sporadically expanded for a parallel SCSI interface, will then be ported with minimal rework to the latter SCSI.

For the terminology of the SCSI command move, communication is established between the initiator (initiator), which sends the command, and the target extension (target), which viconu її.

The SCSI command is located in the Command Descriptor Block (CDB), which consists of the operation code (1 byte) and the command parameters (5 bytes or more). At the end of the meta, turn the status code, which sounds good 00h (“successful reception”) chi 02h (“pardon”) chi 08h (“borrowed”). SCSI commands include 4 categories - N (no data), W (data transfer from initiator to target), R (data read by initiator) and (bidirectional calls).

The transmission protocol is about 60 commands, zokrema:

• re-verification of readiness to attach;
• start/upload attachments (unmute/unmute the disk drive, start/enhance the nose);
• read data (4 command modifications);
• write down data (4 options);
• designate the city (smallness) of the accumulator;
• format extensions (throw all sectors to zero), etc.

The skin attachment on the SCSI bus takes at least one logical number (Logical Unit Number - LUN). Simple extensions take less than one LUN, foldables - no LUNs. For example, a direct access extension (HDD) is composed of a set of logical blocks that sound like addresses (Logical Block Address - LBA). The very LBA variation requires 4 modifications of read/write data commands, some of them vary addresses by 21 bits, others - by 32 bits.

Parallel interface 5С5/. The 8С8І interface, as a rule, is parallel (Fig. 4.24) and physically є flat cable with 25, 50, 68-pin sockets for connecting peripheral devices. Bus 8С8І to replace all lines of data, which are accompanied by a line to control paired

interface

Built-in outbuildings

[Plug

Stub

Vinesі (zvnishnі) annex

Mal. 4.24. Interface 8C $ 1: a- charitable architecture; b - BSB adapter!

stі, that nine keruyuchih lines. The SCSI standard defines two ways of signal transmission: unipolar or asymmetric (Single ended) and differential (Differential). The first type has one wire with a zero potential (“ground”), which transmits signals by data lines with signal equals, which is what TTL logics provide. During differential transmission of the signal for the skin line, two darts were seen, and the signal on this line appeared in the output potentials on the їx outputs. With this, the greatest perestrozakhishchennost is available, which allows to increase the length of the cable.

For the SCSI interface, it is necessary to have “terminators” of narrow supports, so that signals on the ends of the cable can be shrunk and they can be changed. For SCSI vzagali is characterized by a high sensitivity to the quality of the preparation of cables of the same age, as may be different versions of the interface.

SCSI attachments are also connected to a daisy chain, and a SCSI skin attachment has its own address (SCSI ID) in the range 0 to 7 (or 0 to 15). Like the address of the controller board, and the highest value of the SCSI ID - 7(15), the address of the exciting disk (SCSI ID) is "O", the other disk - "1". The exchange between SCSI backbone attachments is determined by the standardized list of commands (Common Command Set - CCS). The software for the SCSI interface does not operate on the physical characteristics of the storage device (such as the number of cylinders, heads, etc.), but on the right only with logical data blocks, so in one SCSI-lane can be placed, for example, a hard scanner. disk and storage CD ROM.

The SCSI controller vibrates once the power is on. When SCSI add-ons are implemented auto-configuration of add-ons (Plug-n-play) behind the SCAM protocol (SCSI Configured AutoMagically), the SCSI ID values ​​are seen automatically. For standardized management of SCSI devices, the ASPI (Advanced SCSI Programming Interface) software interface is widely used.

SCSI indicators. There are more than ten different versions of the SCSI interface (Table 4.8). The main characteristics of the SCSI bus є:

Width - 8 ("narrow", narrow format) or 16 bits ("wide", wide format);

Mal. 4.25. Marking of SCSI attachments with different electrical parameters: / - Single-Ended; 2 - Low Voltage Differential; 3 - High Voltage Differential; 4 - mixed type interface Low Voltage Differential/Single-Ended

Table 4.8. Versions (generation) of the SCSI interface

	speed	Tire width (width)	Max.			maximum number connection
		(wide)
			Not rated for ultra dryness
Ultra3 SCSI or Ultra 160 SCSI					Not recommended for ultra2 dryness
		Not appointed				Not appointed

• bus clock frequency;
• type of electrical signals (Fig. 4.25):
• - unipolar - Single-ended (SE);
• - High-voltage differential - High-voltage differential (HVD) - 5 V;
• - low-voltage - Low-voltage differential (LVD) - 3 tbsp.

On swidkіst vplyvayut mainly two first parameters. Sound stinks are recorded like prefixes before the word SCSI (Table 4.8).

You can calculate the maximum transmission speed of the attachment-controller by taking the bus frequency, and in the case of Wide, multiply it by 2 (for example, FastSCSI - 10 MB / s, Ultra2WideSCSI - 80 MB / s).

Last SCSI interfaces. Some of the recent versions of SCSI, and themselves - SSA (Serial Storage Architecture), FC-AL and Serial Attached SCSI (SAS) appeared to be traditional parallel to the SCSI standard and focused on data transfer for subsequent communications (div. Table 4.8). The main advantages of the last interface are the great speed of data transmission; "hot" inclusion-wimicannia; the worst debility.

Terminators, roses. Linear (Single Ended) and differential (Differential) versions of SCSI, their cables and pinks are identical, but there is no electrical connection between them (Table 4.9).

Differential version for skin signal with twisted pair of conductors and special receivers, with which the total length of the cable is large, saving a high frequency of exchange. Differential interface zastosovuetsya in hard disk server systems, but in great PCs no extensions.

In the linear version, the signal is obliged to go through its own single conductor, twisted (or accepting the other one in a flat cable) with a zero (reversible) drotom.

SCSI-attachments are connected by cables to the lanyard, terminators are connected on the remaining outbuildings. Often one of the last extensions is a host adapter. Vіn mozhe mother for the skin canal, both internal roses and external.

At one-hour change of call and internal rose of the host adapter, the yogo terminator is turned on. The correctness of the choice of terminators in their meaning is the presence of one of the terminators either, navpak, or less

Table 4.9. SCSI interface sockets

DB-25 - connection of the main accessories, mainly scanners, lOmega Zip Plus, the largest extensions for Macintosh (similar to a pink modem)

Low-Density 50-pin or Centronics 50-pin - external connections for scanners, streamers, call SCSI-1

High-Density 50-pin or Micro DB50, Mini DB50 - standard regular narrow-pin

High-Density 68-pin or Micro DB68, Mini DB68 - standard external wide-pin

High-Density 68-pin or Micro Centronics, reserved for outgoing SCSI attachments

Table 4.10. SCSI A-cable connectors

Contact rose		Contact rose

that 32-bit versions of 8С81 (for the 8-bit version, contacts 1-5, 31-39, 65-68 are not tagged); Rating for external connection looks like a miniature Centronics version with flat contacts, internal pins;

• Q-cable, 68-wire extension up to 32 bits, paired with P-cable;
• cable with D-25P plugs - 8-bit, standard for Macintosh, can be used on other external devices (Iomega ZIP-Drive).

Possible different variations of adapter cables.

Tire. As in the PCI bus, the SCSI bus has the ability to exchange information between any pair of attachments. Obviously, most exchanges are carried out between the host adapter and the peripherals. Copying data between attachments can be done without going to the computer's system bus. There are great opportunities for intelligent host adapters from the built-in cache memory. The skin exchange on the tire takes the fate of yogo іnіtіator (Initiator) and tsіl'ovy pristіy (Target). At the table 4.11 to induce the recognition of bus signals.

Table 4.11. SCSI bus signal assignment

	(1 - Initiator, T - Target)	Appointment
		Inverse data bus from bits to parity
		Terminators eating
		Uvaga
		Bus Busy
		Request for resending data
		Response to REQ #
		Target sends an alert
		Select the main building by the initiator or Reselect the main building by the initiator
		Control (0) / data (1) on bus
		Direct transfer of initiator or phase Selection (1) / Reselection (0)

• ny terminator can be brought to inconsistency or waste the practicality of the interface. Cable. The range of 8C81 cables is wide (Table 4.9). The main standardized cables: A-cable (Table 4.10) - standard for 8-bit 8C81 interface 50-wire internal loop (pin ShS-50) or outer screening (pin Goshs8-50); V-cable - 16-bit extension 8С81-2, extension not filled;
• Р-cable - 16-bit 8С81-2/3 68-wire with reduced miniature shielded roses, universal for internal and external cables 8-, 16-

SCSI Hard Disk - This is the hard drive, which is a victorious system, which can be found on most home computers. The first thing is the reason for the fact that a small number of disks can be sequentially connected up to one day. Wines also propagate a higher speed of data transmission, although the difference is often greater in theory, lower in practice. SCSI is especially good for servers and other computer systems that are used for 24/7 desktops. SCSI stands for Interface for small computer systems. Sound like an acronym, but chi is not an abbreviation, and it sounds like “say - scuzzy.” The system can be used to connect to various attachments, although more sound can be connected to SCSI terms and a hard drive.

The largest retailer between SCSI and a hard disk is a competing system, such as SATA or ATA, which can have a SCSI interface and a processor on the disk itself. Tse means that the productivity of the disk does not depend on the specifics of the computer. If you don’t always need to transport SCSI nedolіk for home koristuvach, tse can be an important priority for corporate koristuvachіv, yakі pratsyut on dekіlkoh computers and їm it is necessary to use specialized machines with economical mіrkuvani.

You can use a special adapter to connect more than one SCSI hard drive to one slot on the computer's system board. Leather adapter supports up to 15 discs. The skin disk can be jumpered by a jumper, which can be inserted in the range from 0 to 15 and the skin disk is responsible for inserting into the next row to avoid conflicts. The possibility of using a large number of hard disks is especially important for systems that require a three-fold backup.

SCSI hard drives sound much more expensive, lower SATA and ATA drives have higher capacities. Because part of the vitrates is composed of components to control the disk with SCSI interface. Tse mozhe bring up to a bigger price increase. For example, a SCSI disk can be put in a box, or more times more, less storage with a SATA interface, which may change the capacity.

SCSI disks have historically been small in terms of transmission speed, and other types of hard disks that need to be developed quickly over the course of an hour. A SCSI hard drive will normally wrap around on a hard drive, as it may take an hour to read, write, and access data. SCSI disks are also more suitable for a permanent working computer, and they are not super for types of hard disks, as they are insured and rated for victoria on a home computer for a few days. The number of advantages, and the high price, means that SCSI disks are usually the most suitable for systems that are constantly turned on and actively recycled, such as servers.

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