FastWide SCSI
A type of SCSI capable of transferring data up to 20 megabytes/s on a 16-bit bus.
FastWide SCSI: the 16-bit parallel standard that hit 20 MB/s
FastWide SCSI is a parallel data interface standard that emerged in the early 1990s as an upgrade path for storage and peripherals in industrial systems. It operates on a 16-bit data bus, meaning 16 signal lines carry data simultaneously, and achieves a maximum throughput of 20 megabytes per second. This made it roughly double the speed of the earlier 8-bit Fast SCSI variant, which maxed out at 10 MB/s on a single-wide bus.
The 16-bit width is the defining feature that separates FastWide from narrower implementations. A narrow SCSI bus uses 8 parallel lines; FastWide uses 16. Physically, this meant wider connectors and more pins, typically 68-pin high-density or 80-pin variants rather than the 50-pin Centronics connectors used for narrow buses. The extra pins carry the second byte of data, ground returns, and additional control signals required for the wider protocol.
Where it lived in the trade
FastWide SCSI occupied a specific niche in the 1990s: server storage cabinets, tape backup systems, and industrial imaging equipment that needed better throughput than narrow SCSI but predated the market dominance of Fibre Channel and Serial Attached SCSI (SAS). It was common in Unix workstations and some high-end PC servers. The 20 MB/s limit was adequate for mechanical hard drives and tape cartridges of that era, which rarely saturated the bus on their own.
Termination and cable run length remained critical design concerns, as with all parallel SCSI. Improper termination caused reflections that corrupted data at speed; maximum cable length was typically 3 to 6 meters depending on the specific implementation and quality of shielding. Hot-swapping was not reliably supported in most FastWide implementations, requiring powered-down disconnection to avoid bus faults.
FastWide SCSI is now obsolete in new installations, replaced by Serial Attached SCSI, Fibre Channel, and later SSD interfaces. However, legacy equipment still running in factories and data centers may retain FastWide arrays or backup devices, making familiarity with its pinouts, termination schemes, and speed characteristics relevant for maintenance technicians working on aging hardware.