SCSI History by John B. Lohmeyer July 3, 1990 Spring 1979 -- Shugart Associates began defining the Shugart Associates System Interface (SASI). SASI was one of several industry-defined disk interfaces that works at a logical level instead of at a device level -- this permitted a stable interface in spite of rapid changes to the disk devices. Shugart Associates encouraged disk controller houses to use SASI by putting SASI in the public domain. DTC and OMTI, now DTC QUME and SMS/OMTI, were the two earliest controller houses to build SASI products. Without VLSI interface chips, those products implemented only the minimum of the SASI architecture. 1980 -- Shugart Associates failed in an attempt to get X3T9.3 to accept SASI in place of IPI, the Intelligent Peripheral Interface. Spring 1981 -- Larry Boucher, one of the architects of SASI, left Shugart Associates to found Adaptec, a company that has specialized in SCSI products. Summer 1981 -- NCR explored the possibility of adopting SASI instead of a proprietary interface they had recently defined. Significant issues developed with NCR wanting to add a differential driver/receiver option to improve signal quality and to add a ten-byte command descriptor block option to overcome the limited addressing space of 2**21 logical blocks. Shugart Associates feared market confusion. Negotiations fell through. September 1981 -- Shugart's subsidiary, Optimem, an optical disk drive company, requested longer cable lengths using differential drivers/receivers and an increased addressing space. Shugart Associates' marketing department recognized the inevitable and asked NCR if they were still interested in joining forces to promote SASI as an industry interface. A rapid-fire series of meetings between NCR and Shugart Associates engineers ensued to more completely document SASI and to add a number of features from NCR's proprietary interface. December 1981 -- NCR and Shugart Associates jointly requested that X3T9.3 grant time at their next meeting in February 1982 to examine the joint proposal the two companies were drafting. X3T9.3 agreed to split their next meeting into two parallel sessions, one for IPI (and ISI, which was later dropped) and the second for SASI. February 1982 -- At the conclusion of the split X3T9.3 meeting, the two sessions re-joined and decided that SASI should be assigned to X3T9.2, an existing task group which had no current project. April 1982 -- X3T9.2 met and drafted a formal project proposal for the SCSI, the Small Computer System Interface which was to be based on SASI. 1982 through 1984 -- X3T9.2 met every two months with working group meetings between each meeting to fully document SCSI. During this period, NCR contributed proposed command sets for tapes, processors, and printers. An optical WORM command set was contributed by Optimem. SCSI wasn't just for disks anymore. April 1983 -- NCR announces the NCR 5385, the first SCSI protocol chip. April 1984 -- NCR announces the NCR 5380, the second SCSI protocol chip. The 5380 includes on-chip single-ended drivers/receivers, making inexpensive SCSI implementations a reality. This is the chip that Apple Computer adopted for its Macintosh computers, which put SCSI on the map. April 1984 -- In San Jose California, X3T9.2 voted to forward SCSI to its parent committee to begin the lengthy approval process to become an ANSI standard. June 1985 -- The miniature ribbon shielded connector was added to SCSI after several vendors experienced problems with the AMPmodu connector. July 1985 -- A special working group began a series of meetings to define enhancements to the SCSI command set for disks that eventually became know as the Common Command Set (CCS). June 1986 -- ANSI approved SCSI as ANSI X3.131-1986. June 1986 -- X3T9.2 began the SCSI-2 project to incorporate the Common Command Set into SCSI plus numerous other enhancements. 1986 through 1989 -- X3T9.2 met bimonthly with working group meetings between each meeting to define SCSI-2. This was a period of intense work and SCSI grew from 200 pages to nearly 600 pages. Many features and functions were added and a few options were removed. February 1989 -- X3T9.2 forwarded SCSI-2 beginning its formal approval as an ANSI standard. February 1990 -- X3T9.2 resolved the public review comments on SCSI-2 without making substantive changes. SCSI-2 went on for X3 approval. Comments received concerning adding a single-cable 16-bit solution were resolved by assigning this activity to the SCSI-3 project. July 1990 -- It is expected that SCSI-2 will be approved by X3 on July 4, 1990 and by ANSI later in July 1990. Publication of SCSI-2 will take several months. The mind works on fuzzy logic. If I got some dates wrong or missed some important events, please let me know. I will revise this document periodically. John Lohmeyer