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[ The PC Guide | Systems and Components Reference Guide | Hard Disk Drives | A Brief History of the Hard Disk Drive ]

Early Disk Drives

The very first disk drives were of course experiments. Researchers, particularly those at IBM, were working with a number of different technologies and concepts to try to develop a disk drive that would be feasible for commercial development. In fact, the very first drives were not "disk drives" at all--they used rotating cylindrical drums, upon which the magnetic patterns of data were stored. The drums were large and hard to work with.

The earliest "true" hard disks had the heads of the hard disk in contact with the surface of the disk. This was done to allow the low-sensitivity electronics of the day to be able to better read the magnetic fields on the surface of the disk. Unfortunately, manufacturing techniques were not nearly as sophisticated as they are now, and it was not possible to get the disk's surface as smooth as would be necessary to allow the head to slide smoothly over the surface of the disk at high speed while in contact with it. Over time the heads would wear out, or wear out the magnetic coating on the surface of the disk.

The key technological breakthrough that enabled the creation of the modern hard disk came in the 1950s. IBM engineers realized that with the proper design the heads could be suspended above the surface of the disk and read the bits as they passed underneath. With this critical discovery that contact with the surface of the disk was not necessary, the basis for the modern hard disk was born.

The very first production hard disk was the IBM 305 RAMAC (Random Access Method of Accounting and Control), introduced on September 13, 1956. This beastie stored 5 million characters (approximately five megabytes, but a "character" in those days was only seven bits, not eight) on a whopping 50 disks, each 24 inches in diameter! Its areal density was about 2,000 bits per square inch; in comparison, today's drives have areal densities measured in billions of bits per square inch. The data transfer rate of this first drive was an impressive 8,800 bytes per second. :^)

Over the succeeding years, the technology improved incrementally; areal density, capacity and performance all increased. In 1962, IBM introduced the model 1301 Advanced Disk File.  The key advance of this disk drive was the creation of heads that floated, or flew, above the surface of the disk on an "air bearing", reducing the distance from the heads to the surface of the disks from 800 to 250 microinches.

In 1973, IBM introduced the model 3340 disk drive, which is commonly considered to be the father of the modern hard disk. This unit had two separate spindles, one permanent and the other removable, each with a capacity of 30 MB. For this reason the disk was sometimes referred to as the "30-30". This name led to its being nicknamed the "Winchester" disk drive, after the famous "30-30" Winchester rifle. Using the first sealed internal environment and vastly improved "air bearing" technology, the Winchester disk drive greatly reduced the flying height of the disk: to only 17 microinches above the surface of the disk. Modern hard disks today still use many concepts first introduced in this early drive, and for this reason are sometimes still called "Winchester" drives.

The first hard disk drive designed in the 5.25" form factor used in the first PCs was the Seagate ST-506. It featured four heads and a 5 MB capacity. IBM bypassed the ST-506 and chose the ST-412--a 10 MB disk in the same form factor--for the IBM PC/XT, making it the first hard disk drive widely used in the PC and PC-compatible world.

Next: Key Technological Firsts

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