3B series computers
In 1984, after regulatory constraints were lifted, AT&T introduced the 3B20D, 3B20S, 3B5, and 3B2 to the general computer market,[1][5] a move that some commentators saw as an attempt to compete with IBM.
They were first produced in the late 1970s at the Western Electric factory in Lisle, Illinois, for telecommunications applications including the 4ESS and 5ESS systems.
The Data Manipulation Unit (DMU) provides arithmetic and logic operations on 32-bit words using eight AMD 2901 4-bit-slice ALUs.
The 3B20C was briefly available as a high-availability fault tolerant multiprocessing general-purpose computer in the commercial market in 1984.
Innovations included disk independent operation (DIOP: the ability to continue essential software processing such as telecommunications after duplex failure of redundant essential disks); off-line boot (the ability to split in half and boot the out-of-service half, typically on a new software release) and switch forward (switch processing to the previously out-of-service half); upgrading the disks to solid-state drive (SSD) ; and upgrading the tape unit to CompactFlash.
The machine is approximately the size of a large refrigerator, requiring a minimum of 170 square feet floor space.
Developed in the mid-1980's at the Lisle Indian Hill West facility by the High Performance Computer Development Lab, the system consists of multiple high performance (at the time) processor boards – adjunct processing elements (APEs) and adjunct communication elements (ACEs).
These adjunct processors run a customized UNIX kernel with drivers for SCSI (APEs) and serial boards (ACEs).
The processing boards are interconnected by a redundant low latency parallel bus (ABUS) running at 20 MB/s.
The system calls and peripheral drivers are also extended to allow processes to access remote resources across the ABUS.
The 3B4000 is capable of significant expansion; one test system (including storage) occupies 17 mid-height cabinets.
[1] The 3B2/600,[3] running at 18 MHz, offers an improvement in performance and capacity: it features a SCSI controller for the 60 MB QIC tape and two internal full-height disk drives.
The 600 is approximately twice as tall as a 400, and is oriented with the tape and floppy disk drives opposite the backplane (instead of at a right angle to it as on the 3xx, 4xx and later 500 models).
The 3B2/500 was the next model to appear, essentially a 3B2/600 with enough components removed to fit into a 400 case; one internal disk drive and several backplane slots are sacrificed in this conversion.
