The magnetic storage drum on the Ace Pilot Model

This magnetic drum is used as a medium-speed store in conjunction with a high-speed mercury delay-line store in a serial computer. 262,144 binary digits are stored on 256 tracks, each storing 32 words of 32 binary digits. Information is transferred either to or from a mercury delay line in blocks of 1024 digits, each transfer taking about 12 millisec. The reading and writing heads can be moved axially along the surface of the drum so that each of the 16 pairs of heads has access to 16 tracks.