M-3 cartridge disks

Long-term, power-independent data storage

In addition to the M-3 computers

Information Technology History Exhibition

Structure

The drive rotated the "drum" around a vertical axis, i.e. a metal cylinder with extremely smooth polished and magnetizable sides. The read/write heads were located on horizontal axes, at a very precisely defined distance from the sides of the cylinder.

When writing, the write heads were magnetized with a sufficiently strong direct current, which created magnetized stripes ("lines") on the drum surface with a size corresponding to the width and height of the write/read gap formed in their iron core; when reading, however, the magnetic stripes generated electrical pulses in the read heads. The written data could be erased by exciting the write heads with alternating current.

The magnetic lines formed circular tracks marked by the positions of the heads. The lines

• height (= width of the data bars) and width are the dimensions of the slots,
• the minimum distance within the band is determined by the writing frequency and the speed

determined.

Operation

Data was written to and read back from the data tracks via 8 read/write heads at a speed of approximately 50 Wps (= 200 Bps).

The drum's original total capacity was 1 kW, which the domestic developers increased to 1.6 kW; this allowed the machine to achieve an operating speed of 30 ips.

Program set

There were no operating systems or compilers.

The magnetic drum was controlled by user programs written for the M-3 computer (see there)

Historical curiosities

The drum magazine was a robust, nearly 1 m high structure; up to four of these could be connected to the computer, instead of the original 1 (Soviet); the Hungarian version had 2 machines operating simultaneously.

Resources

Overview: M-3 Drum Memory (video)