ESCON
IBM optical serial interface for mainframe peripheral connections.
ESCON (Enterprise Systems Connection) is an IBM-developed data interface used primarily to link mainframe computers with peripherals like disk storage, tape drives, and IBM 3270 display controllers. It operates as a half-duplex, serial connection over optical fiber. Initially running at 10 MB/s, its speed was later boosted to 17 MB/s, and it can now span up to 43 kilometers.
Introduced in September 1990 alongside IBM’s System/390, ESCON replaced the older, slower (4.5 MB/s) copper-based, parallel Bus and Tag channels that had been used since the 1960s. Optical fiber’s smaller diameter and lighter weight helped reduce installation costs. Its switching capabilities also cut down on space and labor by requiring fewer physical links. ESCON is now being phased out in favor of the much faster FICON, which runs over Fibre Channel.
ESCON enables dynamic channel connection setup and reconfiguration without taking equipment offline or manually moving cables. It uses serial transmission over a pair of fibers. The ESCON Director provides dynamic switching—something not possible with IBM-only products before ESCON—and extends the distance between units up to 60 km over dedicated fiber. Permanent virtual circuits are supported through the switch.
Switching with ESCON offers advantages over point-to-point links. A peripheral that previously could only connect to a single mainframe can now be linked simultaneously to up to eight mainframes, allowing peripheral sharing. The ESCON interface specifications were adopted as ANSI X3.296:1997 by the ANSI X3T11 committee.
- Introduced
- September 1990
- Original data rate
- 10 MB/s
- Later data rate
- 17 MB/s
- Maximum distance
- 43 km
- Interface type
- Optical fiber, half-duplex, serial
- Standard
- ANSI X3.296:1997
Lore & Background
IBM introduced ESCON in September 1990 as part of its System/390 announcement. It replaced the older, slower (4.5 MB/s), copper-based, parallel IBM System/360 Bus and Tag channels technology of the 1960–1990 era mainframes. Optical fiber is smaller in diameter and weight, and hence could save installation costs; space and labor could also be reduced when fewer physical links were required due to ESCON's switching features.
ESCON allows the establishment and reconfiguration of channel connections dynamically, without having to take equipment off-line and manually move the cables. It supports channel connections using serial transmission over a pair of fibers. The ESCON Director supports dynamic switching (which could be achieved prior to ESCON, but not with IBM-only products). It also allows the distance between units to be extended up to 60 km over a dedicated fiber. Permanent virtual circuits are supported through the switch.
ESCON switching has advantages over a collection of point-to-point links. A peripheral previously capable of accessing a single mainframe can now be connected simultaneously to up to eight mainframes, providing peripheral sharing. The ESCON interface specifications were adopted as ANSI X3.296:1997 by the ANSI X3T11 committee.
Reader's Guide
ESCON's significance lies in its role as a transitional technology for IBM mainframe connectivity, replacing the decades-old parallel Bus and Tag channels with a modern optical serial interface. Its use of optical fiber reduced cable size and weight, lowering installation costs, while its switching capabilities allowed dynamic reconfiguration and reduced the number of physical links needed. The ability to connect a peripheral to up to eight mainframes simultaneously represented a major advance in resource sharing. ESCON also extended the practical distance between mainframes and peripherals to 43 km, with the possibility of 60 km over dedicated fiber. However, ESCON is being supplanted by the substantially faster FICON, which runs over Fibre Channel. Its legacy includes the adoption of its interface specifications as an ANSI standard (X3.296:1997) and its use in major storage arrays from vendors such as EMC, Hewlett Packard Enterprise, Hitachi Data Systems, IBM, and Sun StorageTek.
Did You Know?
- ESCON originally operated at 10 MB/s, later increased to 17 MB/s.
- ESCON allows a peripheral to be connected simultaneously to up to eight mainframes.
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