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Small Computer System Interface (SCSI) - Pronounced Scu-zee

SCSI (Small Computer System Interface) is computer interface used in connecting hard drives, scanners and other peripherals. There are several types including :standard, Fast/Wide, Ultra, and Ultra Wide. A SCSI adapter connects to the peripheral.

• To find Hardware SCSI Cards, company tech support links or to get prices on SCSI cards go to the "SCSI Cards Hardware" page.
• For information on ASPI drivers go to the ASPI Information page.

There are several versions of this interface which include...

• Standard SCSI
• SCSI 2
  • Fast - 8-bit, supports up to 7 devices, 10 MB/sec
  • Fast/Wide - 16-bit, supports up to 15 devices, 20MB/sec
• Ultra SCSI
  • Ultra  - 8-bit, supports up to 7 devices, 20MB/sec
  • Ultra Wide - 16-bit, supports up to 15 devices, 40MB/sec
• Ultra2 SCSI (LVD)
  • Ultra 2 SCSI -  16-bit, up to 15 devices, 80MB/sec, compatible with legacy SCSI devices

Typically up to 7 devices can be connected to a single card (up to 15 with newer SCSI cards) and multi-connector cables connect to the card on one end with each device strung along the cable in a daisy-chain fashion.

Termination must be provided at two ends. One end is the SCSI card. The only other device that must be terminated is the device at the very end of the cable chain.

Termination is enabled and disabled by either one of two methods. Either terminating resistor packs are provided or a method such as dip switches or jumpers to enable and disable termination.

The more expensive cards provide both internal and external connectors. The internal connectors are used for devices such as SCSI hard drives and removable hard drives like the Zip or Jaz drives. External devices are usually SCSI scanners and external removable hard drives.

Drivers must be installed to allow the SCSI cards to operate properly. Some cards also have an additional configuration that is performed while the computer boots up. Additionally, you must install drivers for the operating system to use these devices properly. Some cards are supported automatically by certain operating systems like the Windows NT 4.0's support for certain Adaptec cards.

SCSI is a very mature technology and is very stable. The biggest problem with it is that users might not be careful in properly terminating the devices.

Type of plugs used in SCSI adapters -

Internal

• 50-pin flat cable internal connectors
• 68-pin flat cable internal connectors
• 50-pin High Density connectors
• 80-pin SCA (new)

External -

• 25-Pin DB25- 8-bit SCSI (Apple/Mac)
• 50-Pin Centronics - 8-bit SCSI (Up to 5MB/sec)
• 50-Pin MM (HD50) - 8-bit SCSI 2 (Up to 10MB/sec)
• 68-Pin HD - high-density 16-bit Wide, Wide Ultra SCSI 3 (up to 40MB/sec)
• 68-Pin VHDCI - 16-bit Wide Ultra 2 (LVD) SCSI 3 (up to 80MB/sec)

Links

• ...SCSI-2 standard @ std.com Link

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