A new disk file has joined the race to provide vast amounts of digital storage with very fast access times. The newcomer is the IBM 1301 storage unit, the fourth important development in disk files in less than a year. It is IBM's dramatic advance from its first important disk-storage unit, the IBM 350, introduced in 1956.
The 1301 is similar to the original 350 in that it uses 50 disks, of 24-in. diam., rotating in horizontal planes. But there the basic similarity ends. The 1301 uses 50 positioners rather than one or two, cutting maximum access time from 800 to a trifle more than 210 msec. Disks in the 1301 rotate at 1800 rpm, rather than 1200, reducing the maximum access time on an individual track from 50 msec to about 33.
Track density has been raised from 100 to 250 tracks per disk surface, raising the storage from 5 million—or 10 million characters with double-density recording—to 50 or 56 million. Each character is of 6 or 7 bits, depending on the particular computer system with which the file is used.
The 350, often called the Ramac (because it was originally designed for the Random Access Method of Accounting and Control system, Model 305) has 50 magnetic-coated metal disks. A single access arm moves up or down to select the disk, then moves in to the appropriate track. With 200 tracks per disk—100 on each surface—and with 500 characters per track, the Model 350 can store 5 million 6-bit characters.
Four years elapsed before a significant advance was made in disk memories, and then Telex Inc. announced the Telex I and II mass-memory modules. With separate positioning arms for each disk and two read/write heads for each disk surface, the Telex files offered drastically reduced access times, down to a maximum of 200 msec. Larger disks (31-in. diam.), higher bit densities, and as many as 64 disks increased capacity for the Telex II to 88 million 7-bit characters.
Soon after the Telex advance, Bryant Computer Products announced its Series 4000 disk files, with from 1 to 20 disks of 39-in. diam. These could store from 5 million to more than 100 million 6-bit characters with a maximum access time of 167 msec. Disks are mounted in vertical planes, and six or more read/write heads on each disk surface substantially reduce access times.
The need continues for vast amounts of storage with small access times. IBM's 1301 is another answer, but certainly not the final one. (Electronic Design, June 21, 1961, p. 4)
This article provides a nice summary of the early development of disk storage units, although with 24-in. disks, their size was a far cry from today's small units.