SCSI Guide - Small Computer Systems Interface (SCSI)  Explained

What is the history of SCSI, what is it's future?

SCSI (Small Computer Systems  Interface) has been here for a long time. Since the early days SCSI  has set a standard by which computers and devices could communicate.  Transfer speeds at this time were typically 5MByte/sec. Over the  years, to keep pace with computers, SCSI has evolved by bus speeds  increasing and widening the data path. There are plans to increase  the performance to 640MByte/sec, with increased  manageability.

What are the different types of  SCSI?

Single Ended SCSI is a kind of electrical  signal where one wire carries the signal and another wire or shield  is connected to electrical ground.

High Voltage  Differential SCSI (HVD formally referred to as Differential  SCSI) is a kind of electrical connection using two wires, one of  which carries a positive signal (V) and the other a negative signal  (-V). At the receiver the difference between signals is measured  yielding a signal proportional to V. This is intended to cancel out  any noise induced in the wires, on the assumption that the same  level of noise will have been induced in both wires. Often,  twisted-pair wiring is used to try to ensure that this is the case.  This type of SCSI is generally used where long distances of up to  25m are required between end devices. This hardware is very  expensive and now almost obsolete.

Low Voltage  Differential SCSI (LVD) is the latest technology allowing even  faster transfer speeds. This works in a similar fashion to HVD  except with lower voltages and a single integrated circuit reducing  the overall cost.


What about SCSI-I, SCSI-II,  SCSI-III, SCSI-IV and SCSI-V?

These generally refer to  the types of connectors used. With reference to external cables the  following can apply:

Please click on the appropriate link to see  the full range of our SCSI Cables or Adapters.