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SCSI Bus Width


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Q1.Which of the following are true about Ultra 640 SCSI? [Choose 2 best answers].

A. Maximum transfer speed of 640Mbps
B. 16-bit bus
C. 8-bit bus
D. Maximum transfer speeds of 320 MBPS

  Correct Answer: A, B



SCSI Type Transfer speed bus
SCSI-1 5Mbps 8 bit bus
Fast Wide SCSI 2 20Mbps 16 bit bus
Ultra Wide SCSI 3 40Mbps 16 bit bus
Ultra 2 40Mbps 16 bit bus
Ultra2 Wide  80Mbps  16 bit bus
Ultra 3 160Mbps 16 bit bus
Ultra320 320Mbps 16 bit bus
Ultra640 640Mbps 16 bit bus

Device support:

Most older specs: SCSI ID - 0=bootable drive, 7=controller, 1-6=any other devices

SCSI 3 ultra-wide, Ultra320, Ultra640: 16 devices, 0=bootable drive, 15=controller

Internal parallel SCSI cables have two or more 50, 68, or 80-pin connectors attached. External cables have 50 or 68-pin connectors at each end, depending on the specific SCSI bus width supported.

The figure below shows the connectors configuration for 80-pin SCA (Single Connect Attachment):

All of these SCSI types are parallel -- bits of data move through the bus simultaneously rather than one at a time. The newest type of SCSI, called Serial Attached SCSI (SAS), uses SCSI commands but transmits data serially. SAS uses a point-to-point serial connection to move data at 3.0 gigabits per second, and each SAS port can support up to 128 devices or expanders.

All the different SCSI varieties use controllers and cables to interface with devices

Note that older types were given for understanding purpose and you are unlikely to get any question on older SCSI types, such as SCSI-1, and 2.

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