IBM 37xx

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3705 Front Panel

IBM 37xx (or 37x5) is a family of IBM Systems Network Architecture (SNA) programmable communications controllers used mainly in mainframe environments.

All members of the family ran one of three IBM-supplied programs.

  • Emulation Program (EP) mimicked the operation of the older IBM 270x non-programmable controllers.
  • Network Control Program (NCP) supported Systems Network Architecture devices.
  • Partitioned Emulation Program (PEP) combined the functions of the two.

370x series[edit]

  • 3705 — the oldest of the family, introduced in 1972 to replace the non programmable IBM 270x family. The 3705 could control up to 352 communications lines.
  • 3704 was a smaller version, introduced in 1973.[1] It supported up to 32 lines.[2]


The 3710 communications controller was introduced in 1984.[3]

372x series[edit]

The 3725 and the 3720 systems were announced in 1983. The 3725 replaced the hardware line scanners used on previous 370x machines with multiple microcoded processors.[3]

  • The 3725 was a large-scale node and front end processor.
  • The 3720 was a smaller version of the 3725,[4] which was sometimes used as a remote concentrator.
  • The 3726 was an expansion unit for the 3725.

With the expansion unit the 3725 could support up to 256 lines at data rates up to 256 kbit/s, and connect to up to eight mainframe channels.[3]

Marketing of the 372x machines was discontinued in 1989.[5]

IBM discontinued support for the 3705, 3720, 3725 in 1999.

374x series[edit]

  • The 3745, announced in 1988,[6] provides up to eight T1 circuits. At the time of the announcement IBM was estimated to have nearly 85% of the over US$825 million market for communications controllers over rivals such as NCR Comten and Amdahl Corporation.[6] The 3745 is no longer marketed, but still supported and used.[when?]
  • The 3746 "Nways Controller" model 900, unveiled in 1992, was an expansion unit for the 3745 supporting additional token ring and ESCON connections.[7] A stand-alone model 950 appeared in 1995.[8]


IBM no longer manufactures 37xx processors. The last models, the 3745/46, were withdrawn from marketing in 2002.[9] Replacement software products are Communications Controller for Linux on System z and Enterprise Extender.


Several companies produced clones of 37xx controllers, including NCR COMTEN and Amdahl Corporation.[10]


  1. ^ Pugh, Emerson (1991). IBM's 360 and Early 370 Systems. MIT press. ISBN 0-262-16123-0. 
  2. ^ IBM Corporation (1979). IBM 3704 and 3705 Communications Controllers Hardware: Student Text (PDF). 
  3. ^ a b c Edwards, M. (Apr il1, 1985). "Communications Processors Rise to Challenge of Larger, Faster Networks.". Communications News. Retrieved September 8, 2012.  Check date values in: |date= (help)
  4. ^ Horwitt, Elizabeth (May 26, 1986). "IBM Unveils low-end SNA connectivity". Computerworld. Retrieved September 1, 2012. 
  5. ^ Guptill, Bruce (May 29, 1989). "FEPs provide variations on networking theme". Network World. Retrieved September 2, 2012. 
  6. ^ a b Brown, Bob (April 25, 1988). "Low-end FEP market to expand through early 90's". Network World. Retrieved September 2, 2012. 
  7. ^ Cooney, Michael (Sep 21, 1992). "IBM adds rich array of network products". Network World. Retrieved September 2, 2012. 
  8. ^ Guruge, Anura (July 24, 1995). "IBM's Nways: much ado about nothing". Network World. Retrieved September 2, 2012. 
  9. ^ White, Bill; et al. (2006). IBM Communication Controller for Linux on System z V1.2.1 Implementation Guide (PDF). IBM Corporation. p. 2. ISBN 0-738-49665-0. 
  10. ^ Korzeniowski, Paul (December 15, 1986). "Data dialog ditties". Network World. Retrieved September 7, 2012.