Self-powered using the SCSI host termination power, or via USB. 2.35W maximum (500mA) To function without external power via USB, requires SCSI host that supplies terminator power on pin 25 of the DB25 socket 5V via standard 4-pin floppy-drive connector, USB, or self-powered using the SCSI host termination power: Current Draw 2.35W maximum (500mA). USB Attached SCSI (UAS) or USB Attached SCSI Protocol (UASP) is a computer protocol used to move data to and from USB storage devices such as hard drives (HDDs), solid-state drives (SSDs), and thumb drives. UAS depends on the USB protocol, and uses the standard SCSI command set. The SCSI Port driver streamlines the Windows storage subsystem by emulating a simplified SCSI adapter. Storage class drivers load on top of the port driver. This means that you can write storage class drivers for Windows with minimal concern for the unique hardware features of each SCSI adapter.

• Introduction

Introduction

SCSI (Small Computer Systems Interface) is a smart bus,controlled with a microprocessor, that allows you to add up to 15peripheral devices to the computer. These devices can include harddrives, scanners, printers, and other peripherals. High-end singleSCSI boards have two controllers and support up to 30 peripherals on asingle expansion card. An advantage of SCSI is that you can connectseveral peripherals to one host adapter, using only one slot in thebus.

Uses for SCSI

SCSI is widely used in workstations, servers, and mainframes; it isless commonly used in desktop PCs. The advantage of SCSI in a desktopPC is that you can add a scanner and several other drives (forexample, CD-Rs, DVD-RAM, Zip drives), as well as hard drives, to oneSCSI cable chain. This has become less important as alternateinterfaces such as USB and FireWire have becomepopular.

SCSI is useful in network servers, where several hard drives can beeasily set up as a RAID configuration. If one drive fails,it can be removed and a new one inserted, without loss of data, whilethe system is still operational. This feature of RAID hardware iscalled hot-swapping.

You can install SCSI hard drives in a PC that already contains one ormore IDE disk drives. The IDE drive will still be the bootdrive, and the SCSI drives will provide additional storage. An IDEdevice is always the default boot device even if a SCSI hard drive isinstalled and configured as SCSI device number 0. For example, if aSCSI hard drive is on the same computer with an IDE CD-ROM drive, thecomputer will always boot to the CD-ROM drive; the only way aroundthis is to replace the IDE CD-ROM with a SCSI one.

Connecting SCSI devices

SCSI devices are daisy-chained together. External devices have twoports, one for the incoming cable and another for the outgoing cableto the next device. An internal device has a single port that attachesto a ribbon cable with multiple connectors. Some higher-end SCSIcards may have multiple internal ports that allow you to attachmultiple ribbon cables.

Each SCSI device must have a unique ID number; normally you can setthese numbers by flipping rotary switches on external devices or bysetting jumpers on internal ones. The SCSI ID determines the deviceorder, which runs from 7 to 0 and then from 15 to 8. The hostadapter defaults to the highest priority, which is 7.

You must terminate the device at the end of a SCSI chain by eithersetting a switch or plugging a resistor module into the openport. Usually, host adapters default to terminated. If devices areconnected both internally and externally, you must remove the hostadapter termination and apply termination to the ends of both chains.

There are adapters that allow SCSI peripherals to be connected via theparallel port. The parallel port's transfer rate is considerably lessthan that of the SCSI host adapter, but it does provide a means tohook up SCSI devices to laptops. Not all SCSI devices will work on aparallel adapter, and some SCSI devices have their own parallel portadapters. In general, expect transfer rates of around 1MBps whenusing a SCSI-to-parallel-port adapter.

SCSI support

Windows 95, 98, NT, Me,2000, and XP as well as most older Macintoshcomputers provide internal support for SCSI, but Windows3.1 and DOS do not. Newer Macintosh computers supportFireWire rather than SCSI for high-performanceinterfaces. To install SCSI in a Windows 3.1 or DOS computer, you mustadd the appropriate SCSI driver.

More information

This information was adapted from TechEncyclopedia at:

You can find more information on SCSI at:

SCSI standards

• SCSI-1: Uses an 8-bit bus and a 25-pinCentronics-style connector. Supports data rates of 4-5MBps and cansupport up to 7 devices
• SCSI-2: Same as SCSI-1, but uses a 50-pinconnector instead of a 25-pin connector, and supports multipledevices. This is what is most commonly meant as plain SCSI. Cansupport up to 7 devices
• Fast SCSI: Uses an 8-bit bus, but doubles theclock rate to support data rates of 10MBps. Uses a 50-pin connectorand can support up to 7 devices
• Wide SCSI or Fast Wide SCSI: Uses a wider cable(168 cable lines to 68 pins) to support 16-bit transfers. Supportsdata rates of 20MBps and can support up to 15 devices

  Note: The term 'wide' refers to the number of cablelines, not to the physical width of the cable, which is actuallysmaller than a 50-pin 'narrow' SCSI cable.

• 8-bit Ultra SCSI-3: Uses an 8-bit bus, andsupports data rates of 20MBps
• 16-bit Ultra SCSI-3: Uses a 16-bit bus. Supportsdata rates of 40MBps and can support up to 15 devices. Also calledUltra Wide SCSI
• 8-bit Ultra-2 SCSI-3: Uses an 8-bit bus. Supportsdata rates of 40MBps and can support up to 8 devices. This is alsothe first generation of SCSI to use a 'low voltage differential' bus,which means that you will sometimes see Ultra-2 referred to as 'LVD'SCSI.
• Wide Ultra-2 SCSI: Uses a 16-bit bus. Supportsdata rates of 80MBps and can support up to 15 devices
• Ultra3 SCSI: Not a specific protocol, but rathera label that the SCSI Trade Association created to apply to any SCSItechnology that combines Ultra2 SCSI with one or more of five newfeatures as defined by the ANSI SCSI-3 Parallel Interface - 3 (SPI-3)specification. Since Ultra3 does not restrict which features must beincluded, there could be as many as 63 variations that could qualifyas Ultra3 SCSI. It would also be possible that two Ultra3 SCSI devicesmight not communicate at 160MBs because they would not include thesame set of features.
• Ultra 160 SCSI: This is Adaptec's and other SCSImanufacturers' implementation of their interpretation of the Ultra3specification. It was created in response to a controversy arisingfrom the fact that a manufacturer can implement only one of the fivekey features of the SPI-3 standard created by ANSI and still callitself 'Ultra 3 SCSI'. Adaptec and the other manufacturers wanted todistinguish their product by advertising its maximum possible speedof 160MBps. Their standards includes Double Transition Clocking(sending info on both the rise and decay of a clock cycle, whichspeeds data transfer without increasing the controller's clock speed),Cyclical Redundancy Checking (CRC), and Domain Validation (optimumspeed negotiation). Ultra 160 has become the de facto standard, inplace of Ultra 3; later technologies did not follow the 'Ultra 3'naming paradigm by getting named 'Ultra 4' and instead were named'Ultra 360' and 'Ultra 640'.
• Ultra 160+: This is simply Ultra 160 with allfive of the ANSI SPI-3 features built in, instead of just one to fourof them.
• Ultra 320 SCSI: This is a bit more than simply anextension of the Ultra 160. This is a newer generation of SCSIattempting to implement the SCSI-3 Parallel Interface - 4 (SPI-4)standards. It has a faster (80MHz) bus with a wide (16-bit) datapath. As you can tell from the name, 320MBps is the expected top speedof this interface.
• Ultra 640 SCSI: An extension of the previousstandard, this time to 640MBps. This standard never became popular,due to the severe cable length limits required to meet the speed. Mostmanufacturers have skipped over this standard and have chosen toadopt Serial Attached SCSI instead.
• Serial Attached SCSI (SAS): This is the lateststandard attempting to switch over to a serial from a parallelinterface; all the standards mentioned here before this one areparallel interfaces (i.e., multiple wires and connectorsside-by-side). This does mean that SAS will be the firstnon-backwards-compatible SCSI standard, at least where the connectoris concerned. It is meant to use the best features of SCSI, Serial ATA(SATA), and fiber channel disk interfaces, and is expected to havesome compatibility with SATA (one way only; an SAS controller willrecognize a SATA drive, but a SATA controller will not recognize anSAS drive). Transfer speeds start at 3GBps (gigabits per second), andthe standard calls for that to increase to 10GBps by the year 2010.

SCSI connectors and interfaces

• Centronics 50-pin connector: The Centronics50-pin connector was once the most widely used SCSI connector. Anexternal connector only, the Centronics is a SCSI-1 connector thatlooks the same as the Centronics cable that attaches to a parallelport printer. The Centronics 50-pin cable comes in male and femalestyles, and gender changers and cable converters are commonlyavailable. Although used on older SCSI devices and external driveenclosures, this interface is no longer heavily used, due to its slowspeed and short cable lengths.
• High-density 50-pin connector: The high-density50-pin connector is used on scanners and Jaz drives. It is one of themore common SCSI connectors and is usually used to connect SCSI-2devices. Both ends of the cable are usually 50-pin male, while thesockets on the host adapter and external devices are 50-pin female.
• DB 25-pin connector: The DB 25-pin or D Sub 25 isby far the most widely used connector. This connector is used forparallel and serial printers in addition to the many other devicesavailable. Both ends of the cable are usually 25-pin male, while thesockets on the host adapter and external devices are 25-pin female.This cable is almost always an external connector.

  Note: DB-25 SCSI cables are not compatible with andshould not be used as serial or printer cables; serial cables andprinter cables should not be used or attached to DB-25 SCSI adapters.You can short out the SCSI host adapter or the motherboard by usingthe wrong cable. Marking cables is the best way to avoid this. Drivers Marantz USB devices.

• IDC50 connector: The IDC50 is the most commoninternal SCSI connector. It is very similar to the standard IDEinternal ribbon cable. The IDC50 SCSI cable is considerably widerthen an IDE ribbon cable; in fact, it is usually the widest standardinternal cable in use. This is a standard SCSI-2 10MBps internal SCSIcable. Many low-end cables have only two or three connectors, allowingfor one or two devices to be attached to the cable. Seven-devicecables are available, though they are often expensive and require alarge case, as the cables may be four or five feet long.
• High-density 68-pin connector: The high-density68-pin connector is the SCSI connector of choice for SCSI-3 hostadapters and peripherals. There is an internal ribbon cable versionthat looks very similar to the IDC50 connector. Many low-end cableshave only two or three connectors, allowing for one or two devices tobe attached to the cable. Seven-device cables are available, thoughthey are often very expensive and require a large case, as the cablesmay be three or more feet long. Both ends of the external cable areusually 68-pin male, while the sockets on the host adapter andexternal devices are 68-pin female.
• SCA 80-pin Micro-Centronics connector: SCA standsfor Single Connector Attachment, a type of disk drive connector thatincludes connection pins for the power cables as well as the datawires. A SCA connector uses an 80-pin plug and socket to connectperipherals. This connector combines power, data channel, and IDconfiguration for fast installation and removal. SCAconnectors are typically found only on high-end SCSI hard disks. TheSCA interface was designed to provide a standard connection forsystems using drives that can be hot-swapped. SCA makes swapping SCSIhard drives much easier than with traditional SCSI cables,plugs, and sockets. An adapter enables SCA drives to fit into standardSCSI enclosures.
• Serial Attached SCSI SFF 8482: Also called '4xinternal' by some vendors. This is a connector with the same formfactor as SATA with the addition of a 'bump' to key it specificallyfor SAS. (SATA drives can be plugged into SAS controllers, but SASdrives will not function with a SATA controller; hence, the necessityfor the key bump on the connector.) As the name says, it's meant to beused internally, i.e., inside the computer case.
• Serial Attached SCSI SFF 8484: Also called'32-pin' or 'MultiLane'. This is a high density connector usuallyintended to plug into the motherboard, controller, or backplaneitself. Cables with this connector on one end usually have fourindividual SFF 8482 connectors on the other.
• Serial Attached SCSI SFF 8470: Also called '4xexternal' by some vendors. This is simply a version of the SFF 8484that's meant to be used with external (i.e., not located within thecase) drives.

You can find more information about SCA connectors at:

You can find more information about SCSI interfaces and connectors at:

Before mounting the device, you’ll need to configure it via the jumper switch located on the rear of the drive.

SCSI ID setting:

The three leftmost jumpers are used to configure the drive’s SCSI ID number. This can be assigned a value of 0 through 7.

Usually, 7 is reserved for the SCSI host adapter card and 0 is reserved for a SCSI-based C: hard disk drive.

In this case the associated User Guide directs use of a number between 1 and 6, and advises that the factory setting is 3.

Each peripheral attached to a SCSI-2 host adapter card, as well as the card itself, must be assigned a unique SCSI ID number from 0 to 15 (0 to 7 for SCSI-1). A SCSI ID uniquely identifies each SCSI device on the SCSI bus and determines priority when two or more devices are trying to use the SCSI bus at the same time.

Each device on the chain, including the host, must be identified by a unique ID number. One SCSI device must not use the same ID number as another, but they may be numbered non-sequentially. Most SCSI host adapters feature external and internal connectors, with the option for the chain to extend in either or both directions. There’s no relationship between the IDs and the physical position on the bus, but both ends must be electrically terminated with resistors to prevent signal reflections and guarantee data integrity over long cable lengths. Termination comes in several varieties, from physical jumpers or plugs to software configurations.

Here are some general guidelines for SCSI IDs:

• For internal SCSI peripherals, the SCSI ID usually is set by configuring a jumper on the peripheral.
• For external SCSI peripherals, the SCSI ID usually is set with a switch on the back of the peripheral.
• SCSI ID numbers don’t have to be sequential, as long as the SCSI host adapter card and each peripheral has a different number. For example, you can have an internal SCSI peripheral with ID 0, and an external SCSI peripheral with ID 6. Gaps in the sequence of numbers don’t matter.
• SCSI ID 7 has the highest priority on the SCSI bus. The priority of the remaining IDs, in descending order, is 6 to 0, 15 to 8.
• SCSI host adapter cards are normally preset to SCSI ID 7 and should not be changed. This gives it the highest priority on the SCSI bus.
• Most internal SCSI hard disk drives come from the factory preset to SCSI ID 0.
• If you have 8-bit SCSI peripherals, they must use SCSI IDs 0, 1, 2, 3, 4, 5, or 6. SCSI ID 0 is recommended for the first SCSI hard disk drive.

Parity setting:

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• Parity ON (with a jumper)

  – Parity check will be performed.

• Parity OFF (without a jumper)

  – Parity check will not be performed.

Terminator setting:

The terminator setting indicates whether or not a device is the last in the chain:

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• Terminator ON (with a jumper)

  – Use this setting if the CD-ReWriter is the last device in the internal SCSI daisy-chain.

• Terminator OFF (without a jumper)

  – Use this setting if there are other devices in the internal SCSI daisy chain after the CD-ReWriter.

Block Size setting:

• Block Size ON (with a jumper)

  – Block Size is set to 512Byte/sector. Typically used for UNIX workstations.

• Block Size OFF (without a jumper)

  – The normal setting for Windows PCs.