Magnetic tape

Magnetic tape for data storage on mainframe computers. The tape was nine-track for eight data bits and one parity bit. Tape drives of the IBM company could start the tape from standstill to 2,86 m/s speed in 1,5 milliseconds. One reel could hold up to 140 MB. To provide such a quick start without the need to immediately spin up the heavy reels, two loops of free tape were sucked into a vacuum chamber so there was enough time to spin up the reels before the length of the free tape was consumed. Tape systems are still used for data archives up till today. One cassette can hold dozens of terabytes. The common drawback of all tape systems is the long time needed to search a certain segment of data, because the tape has to be rewound at first. Disk or semiconductor memories are much faster.