The IBM 3705 Communications Controller is a simple computer which attaches to an IBM System/360 or System/370. Its purpose is to connect communication lines to the mainframe channel. It was a first communications controller of the popular IBM 37xx series. It was announced in March 1972. Designed for semiconductor memory which was not ready at the time of announcement, the 3705-I had to use 1.2 microsecond core storage; the later 3705-II uses 1.0 microsecond SRAM. Solid Logic Technology components, similar to those in S/370, were used.

The 3705 normally occupies a single frame two feet wide and three feet deep. Up to three expansion frames can be attached for a theoretical capacity of 352 half-duplex lines and two independent channel adapters.

The 3704 is an entry level version of the 3705 with limited features.