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tape gradually became the dominant data-storage medium in computers. Magnetic
tape technology has been continually improved since then and is still in limited use
today, particularly for archived data.
The original concept that eventually grew into the
magnetic disk
actually
began to be developed at MIT in the late 1930s and early 1940s. By the early 1950s,
several companies including UNIVAC, IBM, and Control Data had developed
prototypes of magnetic ''drums'' that were the forerunners of magnetic disk
technology. In 1953, IBM began work on its 305 RAMAC (Random Access
Memory Accounting Machine) fixed disk storage device. By 1954 there was a
multi-platter version, which became commercially available in 1956, Figure 1.8.
During the mid-1960s a massive conversion from tape to magnetic disk as
the preeminent data storage medium began and disk storage is still the data storage
medium of choice today. After the early fixed disks, the disk storage environment
became geared towards the removable disk-pack philosophy, with a dozen or more
packs being juggled on and off a single drive as a common ratio. But, with the
increasingly tighter environmental controls that fixed disks permitted, more data per
square inch (or square centimeter) could be stored on fixed disk devices. Eventually,
the
disk drives
on mainframes and servers, as well as the fixed disks or ''hard
drives'' of PCs, all became non-removable, sealed units. But the removable disk
concept stayed with us a while in the form of PC diskettes and the Iomega Corp.'s
Zip Disks, and today in the form of so-called external hard drives that can be easily
moved from one computer to another simply by plugging them into a USB port.
These have been joined by the laser-based, optical technology
compact disk
(CD),
introduced as a data storage medium in 1985. Originally, data could be recorded
on these CDs only at the factory and once created, they were non-erasable. Now,
data can be recorded on them, erased, and re-recorded in a standard PC. Finally,
solid-state technology has become so miniaturized and inexpensive that a popular
option for removable media today is the flash drive.
FIGURE1.8
IBM RAMAC disk
storage device, circa 1956
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