Random Access Memory: Disk Packs To Solid State Drives
The original disks, back in the 1950s and 1960s, came in the form of disk packs that sat on top of disk drives. A single drive topped by a disk pack would come up to an average adult male operator’s navel. The disks were 24 inches in diameter with 100 tracks on each and the first disk packs had 50 disks mounted one above the other with space between to allow the heads to move in and out in search of data.
These were the first RAM (Random Access Memory) devices and were a great step forward in speed, because what had gone before was SAM (Sequential Access Memory) in which the data would be stored on a medium such as paper tape and the tape reader might have to go all the way through a tape in one direction to read the record it wanted, and then all the way back in the other to find the next record. With random access memory, the operating system held the coordinates of each record and sent the heads direct to the required record. Regular backups were taken and the backup disk packs removed to safe storage because from time to time, a head would touch the surface of the disk (or simply fall on it in the event of a power cut) and this “head crash” could corrupt the record stored at the place of the crash or, in the worst case, corrupt the whole disk.
In common with everything else in computing, disk drives have improved beyond all measure over the years. Today, a hard disk that would hold 1,000 times the amount of data one of those big 1950s disk packs could encompass is a tiny fraction of the old one’s size, much faster in operation – and head crashes are rare, even on a laptop that is being moved during a read/write operation.
And now there are Solid State Storage Drives (SSDs) that have no moving heads, keep all date much closer together and so return data faster than ever before.