UNIVAC FASTRAND information

FASTRAND was a magnetic drum mass storage system built by Sperry Rand Corporation (later Sperry Univac) for their UNIVAC 1100 series and 418/490/494 series computers. A FASTRAND subsystem consisted of one or two Control Units and up to eight FASTRAND units. A dual-access FASTRAND subsystem included two complete control units, and provided parallel data paths that allowed simultaneous operations on any two FASTRAND units in the subsystem. Each control unit interfaced to one (optionally two) 1100 Series (36-bit), or 490 Series (30-bit), parallel I/O channels.

A voice coil actuator moved a bar containing multiple single track recording heads, so these drums operated much like moving head disk drives with multiple disks. The heads "flew" on self-acting hydrodynamic air bearings. The drums had a plated magnetic recording surface. An optional feature called Fastband included 24 additional tracks with fixed read/write heads. This feature provided rapid access (35 ms. average access time), and a write lockout feature.

The Fastrands were very heavy (5,000 pounds) and large, approximately 8' long. Due to their weight, FASTRAND units were usually not installed on "false floor", and required special rigging and mounts to move and/or install. There were reported cases of drum bearing failures that caused the machine to tear itself apart and send the heavy drum crashing through walls.

At the time of their introduction the storage capacity exceeded any other random access mass storage disk or drum.

There were three models of FASTRAND drives:

• FASTRAND I had a single drum. The large mass of the rotating drum caused gyroscopic precession of the unit, making it tend to spin on the computer room floor as the Earth rotated under it. Very few of these devices were delivered.
• FASTRAND II (the majority of units produced) had two counter-rotating drums to eliminate the gyroscopic effect. One actuator bar with heads was located between the drums.
• FASTRAND III, introduced in 1970, was physically identical to the FASTRAND II, but increased the recording density by 50%.