Carousel memory

Carousel memory is a type of secondary storage for computers, which was created by Swedish computer engineers Erik Stemme [sv] and Gunnar Stenudd. It was first shown at an exhibition in Paris in 1958.

The FACIT ECM 64, manufactured by Swedish company Facit AB, is a prototype of carousel memory. To avoid having a single, long magnetic tape, it instead has 64 small rolls of 9 meters each, with 1.6-cm wide tape on each roll, divided into eight channels per roll. The tape speed is 5 m/s. To read a particular roll, the carousel rotates so the desired roll ends up at the bottom. A counterweight sits at the free end of the tape, and facilitates the roll in moving out and down into a mechanism with a read-and-write head. The tape is then rewound. The average seek time is 2 seconds and the storage space is 2560 kilobytes. The control system is operated by transistors. Both the carousel and individual spools are replaceable.

The magnetic tape is a 5/8-inch (1.6 cm) wide and 0.05 mm thick Mylar 3M Co type 188.The storage density is specified to 8 bits/mm, and the access head is capable of simultaneous read/write operations. The power requirement is three-phase 380 volts 50 Hz with 300 W when in standby and 750 W when active. Signaling for data uses eight parallel -20 V to 0 V 5 μs pulses.

Peak transfer speed is 182,044 bits/s, using eight parallel lines and thus 22,756 bits/s per line.

The first delivery of the Facit EDB 3 computer was in 1958 (to ASEA in Västerås) used the carousel memory Facit ECM 64.

• BESK, Sweden's first electronic computer, also developed by Erik Stemme
• Exatron Stringy Floppy, 1978 endless tape drive
• Karlqvist gap, calculation of magnetic field in ferromagnetic layer
• Rotronics Wafadrive, 1984 endless tape drive
• ZX Microdrive, 1983 endless tape drive

• Karlqvist, Olle (March 1962), "Applications to the magnetic tape storage unit, facit ECM64 (the Carousel Memory)", BIT Numerical Mathematics, 2 (1): 16–20, doi:10.1007/BF02024778