SCSI-2
The limited acceptance, but great potential, of SCSI-1 led to a more robust standard with a range of commands and a layered set of drivers. The result was a high-performance interface that began to take over the high-end market. It was the interface of choice for fast hard disk drives, optical drives, scanners, and fast tape technology.
One of the most important parts of the SCSI-2 specification is a larger (and mandatory) standard command set. Recognition of this command set (18 commands) is required for a device to be SCSI-2 compliant. The Common Command Set (CCS) made compatibility of multivendor devices possible. The CCS also introduced additional commands to more easily address devices such as optical drives, tape drives, and scanners.
SCSI-2 also supports:
- Wide (16-bit) SCSI.
- Fast SCSI.
- Fast/Wide (combines fast and wide features).
- Ultra (32-bit) SCSI SI-2.
- Backward compatibility with SCSI-1.
Fast SCSI-2
This standard uses a fast synchronous mode to transfer data, doubling the data transfer speed from 5 MB/s to 10 MB/s. Wide SCSI doubles that again.
Plug and Play SCSI adapters first arrived with the advent of the SCSI-2 standard. Today, all new SCSI host adapters are Plug and Play. The SCSI-2 standard took a long time to gain final approval, requiring agreement by many vendors. As a result, you might run into products labeled "Draft SCSI-2." In almost all cases, you can get these products running on any SCSI-2 or later system if you get the appropriate drivers from the vendor or the maker of the host adapter or operating system.