SCSI evolved from the Shugart Associates Systems Interface or
SASI, which was originally created in 1979. The first SCSI standard was approved by
ANSI in 1986 as standard X3.131-1986. To avoid confusion when subsequent SCSI standards
came out, the original specification was later renamed "SCSI-1".
SCSI-1 defines the basics of the first SCSI buses, including cable length, signaling characteristics, commands and transfer modes. It was quite limited, especially by today's
standards, and defined only the most fundamental of SCSI features and transfer modes.
Devices corresponding to the SCSI-1 standard use only a narrow (8-bit) bus, with a 5 MB/s
maximum transfer rate. Only single-ended transmission was
supported, with passive termination. There were
also difficulties associated with the standard gaining universal acceptance, due to the
fact that many manufacturers implemented different subsets of its features. The standard
did not call for all devices to implement support for the same commands, so there was no
guarantee that any given device would work with any other!
SCSI-1 is now obsolete, and the standard has in fact been withdrawn by ANSI. Devices
that adhere to the SCSI-1 standard can in most cases be used with host adapters and other
devices that use the higher transfer rates of the more advanced SCSI-2 protocols, but they
will still function at their original slow speed.
Note: Since all SCSI-1
devices are single-ended, they may cause performance degradation if placed onto a
multimode LVD SCSI bus. If you want to run LVD devices to
their full potential, you will want to avoid mixing them with single-ended devices.
Next: SCSI-2
