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
