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History 2003: Jukebox of 128 Magnetic Rigid Disks

Of same format as vinyl 45rpm audio records

The Federation des Equipes Bull in France is a veritable museum of ancient computer pieces that date from the time when Bull was actually a manufacturer.

One of them, a rotating disk jukebox of the Wurlitzer variety, is something of a wonder. The carousel holds 128 magnetic disks, apparently rigid. This was the first we’d ever heard of a magnetic hard disk library.

The only information we could glean on the strange product, probably built by RCA, are the following: it contained 128 disks of the same format as vinyl 45rpm audio records; each side contained 2 parallel spiral tracks; one track held ten “cells,” each with capacity of 900 characters; since it was possible to read and write on both of the disk’s sides (suggesting that it had 2 magnetic heads), we get a total capacity of 36,000 characters per disk, and a total of 4.6 million characters for the jukebox; average access time to a given cell was 4.25s, with transfer rate of 2,500 characters per second in read or write.

Two jukeboxes could be connected to a central Gamma 30 computer, and eventually even 4, with an additional controller. Thus, we get a maximum capacity of around 28 million characters. On the Gamma 30, 6-bits caracters were represented as 2 bytes.

The small brochure the Federation provided us indicates that this odd device was intended to store data that didn’t require fast times. The example given is that of certain portions of software, where it would be too expensive to record them in the central memory (in magnetic core technology of up to 40K characters), such as those used only at the start and end of processing. For the programming, 2 instructions were necessary, one for the choice of the disk, the other for selecting the positioning of the desired information.

Unfortunately, we were unable to get more information about its inventors, its price, even whether it was ever really put on the market or from when it dates (we know only that the Gamma 30, developed by RCA under the name RCA 301, was sold by Compagnie des Machines Bull between 1961 and 1965, along with Siemens in Europe and ICT in the UK under the name ICT 1501 ).

This article is an abstract of news published on issue 180 on January 2003 from the former paper version of Computer Data Storage Newsletter.

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