Inside the Bendix G-15's Magnetic Drum Memory

The Bendix G-15 vacuum tube computer used a rotating magnetic drum for its main memory. Except for a few registers internal to the processor, all system memory was kept on the drum, as described in the 2023-08-21 post, “Magnetic Drum Memory from a 1950s Bendix G-15 Vacuum Tube Computer”. Unfortunately, this means that when the vicissitudes of time and entropy (water damage and fungus) cause catastrophic head crashes, the computer that relied on it is nothing more than a large, heavy, and expensive boat anchor.

Refurbishing a crashed drum is a wizard-scale undertaking, especially if the crash not only damaged the surface of the drum but also the fixed heads that read and write data to it. Deferring that, discovery of another system with an apparently intact drum provides the option of a transplant. But first, the crashed drum must be removed, providing an opportunity to assess the damage.

Unlike modern hard discs, which are hermetically sealed, only a cork gasket protected the G-15 drum from the environment. The way they dealt with infiltration of dust is both clever and scary.