Hard Disks

Hard Disks

Initial mainframes were mostly magnetic-tape based. They would read in a program from tape, compile it, run it, and write the results back to another tape. There were no disks and no concept of a file system. That began to change when IBM introduced the first hard disk - the RAMAC (RAndoM ACcess) in 1956. It occupied about 4 square meters of floor space and could store 5 million 7-bit characters, enough for one medium-resolution digital photo. But with an annual rental fee of $35,000, assembling enough of them to store the equivalent of a roll of film got pricey quite fast. But finally prices came down and primitive file systems were built up.

Typical of these new developments was the CDC 6600, introduced in 1964 and for years by far the fastest computer in the world. Users could create so-called "permanent files" by giving them names and hoping that no other user had also decided that, say, "data" was a suitable name for a file. This was a single-level directory. Finally, mainframes developed complicated hierarchical file systems, perhaps ending in the MULTICS file system.

As minicomputers came into use, they ultimately also had hard disks. The standard disk on the PDP- 11 when it was introduced in 1970 was the RK05 disk, with a capacity of 2.5 MB, about half of the IBM RAMAC, but it was only about 40 cm in diameter and 5 cm high. But it, too, had a single-level directory in the beginning. When microcomputers came out, CP/M was originally the dominant operating system, and it, too, supported just one directory on the (floppy) disk.


file system, mainframes, minicomputers