Univac FASTRAND Mass Storage Subsystem

For more information on the Univac FASTRAND mass storage subsystem, see the Fourmilab Univac Memories page, “The FASTRAND II”. You can see how large the FASTRAND was from the title card in the video. What isn’t apparent is that this drum unit weighed two and a half tons and often required special reinforcement beneath the raised floor on which it was installed. Up to eight of these storage units could be attached to one control unit, and multiple controllers could be connected to a Univac 1100 series or 400 series computer.

The FASTRAND provided the first persistent on-line file storage for Univac mainframe computers. What was the storage capacity? Well, it’s complicated. Here’s an explanation from Univac Memories:

Since the UNIVAC 1100 series machines to which the FASTRAND II was connected used 36-bit words rather than 8-bit bytes, it isn’t possible to precisely compare the capacity of a device such as the FASTRAND II with contemporary byte-oriented disc drives. Calculating the total capacity in bits and dividing by 8 yields a total capacity of 99 megabytes, but since UNIVAC software in the FASTRAND era used 6-bit FIELDATA character codes (by the time ASCII came into wide use, most FASTRANDs had been retired in favour of a variety of disc drives), the capacity in terms of contemporary computer documents was 132 million characters. When UNIVAC adopted ASCII in the 1100 series, they stored 4 characters in the four 9-bit fields of each 36-bit word, so the capacity of a FASTRAND II in terms of ASCII characters would be 88 megabytes. The same considerations apply to calculations of the transfer rate.

In 1968, each FASTRAND storage unit cost US$ 134,400 and the controller US$ 41,680. In 2023 BidenBucks, that’s equivalent to US$ 1,182,704 for the storage unit and US$ 366,779 for the controller. So, that’s about a million and a half bucks for around a hundred megabytes of storage.

Here is a look inside the suitcase-sized analyser and sector generator used by field engineers (Mr FASTRAND Fix-It) both for regular preventive maintenance and dealing with problems.