Datasheet

one way while the other half are magnetized the other way in a completely random way.

No pattern exists, and the coating is “blank.”

THE INTRODUCTION OF THE HARD DRIVE

Tape is an excellent magnetic medium for recording, but it has two

weaknesses: 1) it is a contact medium that must rub against the

magnetic head for the transfer of the magnetic field to and from the

head, and 2) it is a longitudinal medium—it takes a much longer time

to access a spot on the tape. The first weakness results in both tape

and head wear over time. The second makes it difficult to retrieve

information quickly--it’s easier and faster to find a track on an LP

record than it is on a cassette. IBM engineers in the early 1950s

decided to combine the advantages of magnetic recording with the

advantages of the vinyl record. In 1956 they introduced the IBM 305

RAMAC (Random Access Method of Accounting and Control). It

stored a mere 4.4 megabytes of information spread over 50 discs,

each of which was 2 feet (0.6 meters) in diameter.

The innovative part of the design was that the head did not contact the

discs but sat in a robotic access arm that positioned itself just above the discs in order to avoid

touching them and to prolong the life of both discs and head. By 1962 IBM had designed heads

that literally flew over hard discs by riding a cushion of air. When a computer “crashed,” it

usually described exactly what the magnetic head physically did. Figure 2 shows relative sizes

of the types of debris that can cause head crashes.

RAMAC’s 50

latters

Design goals for magnetic recording have always included increasing the density of

magnetic recording and shrinking the size of the media and the recorders. The huge disc

arrays and disc packs of the 1950s have given way to small, then mini, and now micro

hard drives that hold a thousand times more data in a form factor not much larger than a

control button on the earliest drives. The size, speed, and materials have changed; but

the principles behind even the most advanced micro hard drives are those Oberlin Smith

outlined over a hundred years ago.

Flying Head

Head Fly Height

Magnetic Disc Platter

Human Hair

Dust Particle

Smoke Particle

Fingerprint

Relative Height of Debris

on a Hard Disc Platter

Figure 2