The clauses contain material as described below.
Clause 1 describes the scope.
Clause 2 lists the normative references.
Clause 3 provides a glossary common to the whole document.
Clause 4 provides descriptions and conventions.
Clause 5 describes the physical characteristics.
Clause 6 describes the logical characteristics of the interface.
Clause 7 describes the SCSI command and status structure.
Clause 8 specifies those commands that have a consistent meaning for all device types.
Clause 9 specifies commands for direct-access devices.
Clause 10 specifies commands for sequential-access devices.
Clause 11 specifies commands for printer devices.
Clause 12 specifies commands for processor devices.
Clause 13 specifies commands for write-once devices.
Clause 14 specifies commands for CD-ROM devices.
Clause 15 specifies commands for scanner devices.
Clause 16 specifies commands for optical memory devices.
Clause 17 specifies commands for medium changer devices.
Clause 18 specifies commands for communications devices.
Annex A illustrates SCSI signal sequence.
Annex B illustrates fast SCSI skew time.
Annex C describes other SCSI standardization activities.
Annex D contains SCSI-2 additional sense codes and operation codes in numeric order.
Annex E contains the list of SCSI-2 vendor identifications.
The SCSI protocol is designed to provide an efficient peer-to-peer I/O bus with up to 16 devices, including one or more hosts. Data may be transferred asynchronously at rates that only depend on device implementation and cable length. Synchronous data transfers are supported at rates up to 10 mega-transfers per second. With the 32-bit wide data transfer option, data rates of up to 40 megabytes per second are possible.
SCSI-2 includes command sets for magnetic and optical disks, tapes, printers, processors, CD-ROMs, scanners, medium changers, and communications devices.
In 1985, when the first SCSI standard was being finalized several manufacturers wanted to increase the mandatory requirements of SCSI and to define further features for direct-access devices. Rather than delay the SCSI standard, formed an ad hoc group was formed to develop a working paper that was eventually called the Common Command Set (CCS). Many disk products were designed using this working paper.
In parallel with the development of the CCS working paper, work began on an enhanced SCSI standard which was named SCSI-2. SCSI-2 included the results of the CCS working paper and extended them to all device types. It also added caching commands, performance enhancement features, and other worthwhile functions. While SCSI-2 has gone well beyond the original SCSI standard (now referred to as SCSI-1), it retains a high degree of compatibility with SCSI-1 devices.
SCSI-2 has evolved significantly from SCSI-1 with the new document nearly three times larger. Most of the changes are additions, but several obsolete options were removed:
There are several new low-level requirements:
Several low-level options were added:
New command sets were added including:
All command sets were enhanced: