|WWW Virtual Library for SCSI
The Small Computer Systems Interface
Jan. 10 - 14, 2011
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WWW VL/SCSI -- Getting Listed:
SCSI: Brief History
The roots of SCSI go back to 1979, when the disk drive manufacturer Shugart was looking for a new universal interface for future disk drives. The goal of the effort was to develop an interface that supported logical block addressing rather than head/cylinder/sector, 8-bit parallel data transfer instead of analog serial and generic commands rather than a couple of control lines. This interface was called SASI (Shugart Associates Systems Interface). The SASI specification included some 6-byte commands and a single-ended interface.
In late 1981, Shugart along with NCR, presented SASI to the ANSI committee X3T9.2, which accepted it as a project, now called SCSI. In the following development period, many major improvements over SASI have been added to the SCSI draft. This includes the ability of devices to compete for the bus (arbitrate) and to free the bus (disconnect/reselect) temporarily during command execution. Also it was now possible to have more than one host adapter on a SCSI bus. By 1984 a draft proposal was presented to ANSI for approval. At that time there were already many devices on the market that adhered more or less to this proposal. In 1986, SCSI was approved by ANSI as document X3.131-1986. This first official version is today referred to as SCSI-1. SCSI-1 included 6- and 10-byte commands, the single-ended and differential interface options and synchronous and asynchronous data transfer.