Overview
ISO/IEC 9316:1995 (Second edition, 1995) - commonly known as SCSI-2 - is an international standard that defines a Small Computer System Interface bus for interconnecting computers and peripheral devices. The standard extends and refines the original ISO 9316:1989 (SCSI‑1), providing more complete normalization of the SCSI command set and detailed mechanical, electrical and functional specifications to enable device interoperability.
Key topics and technical requirements
ISO/IEC 9316:1995 covers a comprehensive set of technical subjects essential to SCSI‑2 implementations, including:
- Physical characteristics
- Cable types and requirements (single‑ended and differential)
- Connector alternatives (shielded and non‑shielded)
- Mechanical and connector contact assignments
- Electrical characteristics
- Input/output signal behavior, terminator power and reserved lines
- SCSI bus topology and signal sources
- Timing and signaling
- Detailed bus timing parameters (arbitration delay, assertion period, bus free/set/settle delays, cable skew, transfer period)
- Fast synchronous transfer options and fast‑path timing constraints
- Logical characteristics
- SCSI bus phases (BUS FREE, ARBITRATION, SELECTION, RESELECTION, COMMAND, DATA, STATUS, MESSAGE)
- Phase transitions, signal restrictions and bus conditions (attention, reset - hard and soft)
- Message system and a catalog of SCSI messages (IDENTIFY, ABORT, DISCONNECT, QUEUE TAGs, SYNCHRONOUS/WIDE TRANSFER REQUEST, etc.)
- Command set and device behavior
- Command Descriptor Block structure, operation codes and status reporting
- Command processing, queued I/O (tagged/untagged), contingent allegiance and unit attention conditions
- Standard commands and parameters for all device types (INQUIRY, REQUEST SENSE, MODE SENSE/SELECT, READ/WRITE variants)
- Device classes
- Direct‑access devices (disk drive model, defects, format, read capacity and related commands)
- Parameters, mode pages and vital product data definitions
Applications and who uses it
ISO/IEC 9316:1995 is used by organizations and professionals who design, build, test or integrate storage and peripheral hardware and firmware:
- Hardware designers and connector/cable manufacturers - to implement correct mechanical and electrical interfaces for SCSI‑2 devices.
- Storage device manufacturers (direct‑access devices) - to implement command sets, mode pages and media handling behavior.
- Firmware and driver developers - to support SCSI phases, message protocols, queued I/O and error handling.
- System integrators and OEMs - to ensure interoperability across host adapters, controllers and peripherals.
- Test labs and compliance engineers - to validate timing, signaling and functional conformance for certification.
Related standards
- ISO/IEC 9316:1989 - SCSI‑1 (original Small Computer System Interface), which SCSI‑2 extends and clarifies.
Keywords: ISO/IEC 9316:1995, SCSI‑2, Small Computer System Interface, SCSI bus, connectors, cable requirements, SCSI commands, timing, direct‑access devices, interoperability.
