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Table Of Contents  CertiGuide to A+ (A+ 4 Real)
 9  Chapter 10: The Small Computer System Interface, SCSI

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A Little Background

In 1971, IBM introduced the first "memory disk", as it was called then, or the "floppy disk" as it is known today. The first floppy was an 8" plastic disk coated with magnetic iron oxide; data was written to and read from the disk's surface. IBM engineers led by Alan Shugart invented the "floppy".

In 1976, the 5 1/4" the flexible disk drive and diskette was developed by Alan Shugart for Wang Laboratories. Wang had wanted a smaller floppy disk and compatible drive to use with their desktop computers. By 1978, more than 10 manufacturers were producing 5 1/4" floppy drives.

SCSI began life in 1979 conceived by Shugart as a universal interface for fu-ture disk drives. The idea was to develop an interface that supported logical block addressing instead of the head/cylinder/sector parameters; 8-bit paral-lel data transfer instead of serial and generic commands instead of control lines. Shugart Associates Systems Interface (SASI) was developed which in-cluded some 6-byte commands and a single-ended interface.

Shugart wanted to get his system made into an ANSI standard.95 In 1981, Shugart Associates teamed up with NCR Corporation and convinced ANSI to set up a committee to standardize the interface. In 1982, the X3T9.2 com-mittee was formed to work on standardizing SASI. Changes were made to the interface to widen the command set and improve performance. The name was changed to SCSI, since having "Shugart Associates'" name on the interface would have implied that it was proprietary and not an industry standard. The first SCSI interface standard was published in 1986, and evo-lutionary changes to the interface have been occurring steadily ever since that time.


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95. http://www.pcguide.com/ref/hdd/if/scsi/over-c.html

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