hard drive history

beginings: mfm drives of the 1980s

Miniscribe 3053

Photo: Red Hill.

Miniscribe 3053

Miniscribe is remembered now for ugly mass market drives like the dreadful 3650, but there was a lot more to Miniscribe than cheap, slow and noisy. This beautifully made drive is an example.

In the specifications table, notice the odd number of heads. Up until about 1998 or so, this was a sure sign of a fast, precise voice coil acuator instead of a slow, noisy, unreliable stepper.

Like all voice coil drives of this era, the 3053 had an extra head which was not used to store user data: its only purpose was to read positioning information which could then be used to place the remaining heads right over the centre of the data tracks.

The beauty of this system was that thermal expansion and contraction — the perennial enemy of all stepper drives — was a complete non-issue. For example, when the drive was cold and the platters shrank, the location of the data tracks still changed (just as it did in a stepper drive), but the location of the callibration tracks changed too, so adjustment of the seek mechanism was automatic and read-write operations was unaffected.

In a premium drive like this one, the "wasted" space on the unused sixth surface was acceptable — speed and reliability mattered much more than a little extra capacity. Really high-capacity drives often had as many as a dozen discs, meaning that the loss of a single surface was unimportant. But for everyday drives with just one or two discs, it was significant, and voice coil actuators couldn't move into the mainstream until the invention of the embedded servo which allowed the use of all surfaces.

Illustration: a 3053 pictured with an assortment of Miniscribe 3½ inch drives, mostly 8425s. This one was manufactured during 1988. Notice the care with which the top cover has been cast.

Performance0.24Reliabilityno data
Data rate5 Mbit/secSpin rate3600 RPM
Seek time25ms ActuatorVoice coil
Platter capacityMBInterfaceMFM
AT drive type?Form5.25" inch half-height
305344.68MB5 thin-film heads1987