IBM 37xx

• 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]

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.

• 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 The last models, the 3745/46, were withdrawn from marketing in 2002.^[9] Replacement software products are Communications Controller for Linux on System z and Enterprise Extender.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]