SCSI-1
In the late 1970s, Shugart Associates developed an interface to handle data transfers between devices, regardless of the type of device. The interface operated at the logical-or operating system-level instead of at the device level. This new interface was called the Shugart Associates System Interface, or SASI-the precursor to SCSI.
In June 1986, the ANSI X3.131-1986 standard known as SCSI-1 was formally published. This was a very loose definition, with few mandates. As a result, manufacturers of SCSI products developed a variety of competing designs.
SCSI-1 supported up to seven devices on a chain (plus the host adapter). Each device transferred data through an 8-bit parallel path. Compatibility of SCSI drives was nearly impossible because many SCSI devices had their own custom commands on top of the limited SCSI standard.
You might encounter older SCSI adapters, drives, and peripherals that are based on the original SCSI-1 standard. In reality, this standard amounts to little more than a few agreed-upon commands. The wide range of proprietary drivers, operating system interfaces, setup options, and custom commands made true compatibility a real problem and gained SCSI a bad reputation on the PC platform. It was, however, popular with Apple and UNIX developers, who could work with a limited range of devices.
In most cases it is best to upgrade any SCSI-1 devices to SCSI-2. If circumstances require you to work on an early SCSI product, you will have to contend with both hardware and driver issues. Check the Web site of your SCSI device's manufacturer for possible new drivers.