The AT&T 3b2 400 was a UNIX based 32-bit super micro computer developed by Bell Laboratories for exclusive use by AT&T. It soon became available publicly for around $20,000 to $25,000 depending on the installed RAM. It used a Western Electronic 32100 processor running at 10MHz. The computer was designed to be a server for multiple workstations, capable of connecting 46 users through its 12 expansion slots.

Below is a review of the unit I picked up from a Craigslist ad for $40.