hard drive history

smaller, faster: early 3.5 inch drives

Miniscribe 8438

Photo: Red Hill.

Miniscribe 8438 and 8425

An interesting pair of drives, identical except for the badge. Miniscribe was Seagate's biggest competitor for the mass market during the late eighties and the 8425/8438 twins were a major part of Miniscribe's quest for overall market leadership. They sold in vast numbers.

→ A pair of the new-style three and a half inch drives that were making Seagate's ST-225s look very dated. On top, an immaculate late-model 8425 which left Miniscribe's Singapore production line on 15th August 1989. Underneath, an 8438 dated 28th March 1988. Almost fifteen years later, both were still working perfectly. Notice the 8438's large black and silver stepper motor at lower right.

The 8438 was a neat, modern looking 3.5 inch 30MB stepper drive with factory-certified RLL capacity. The 8425 was the exact same drive without the certification. In practice, Miniscribe mass-produced drives and then tested them. The very best units were sold as higher-value 8438s, the also-rans as cheaper 8425s. Of course, there was nothing to stop you buying a 20MB 8425 and putting it with an RLL controller to get 30MB — except that it wasn't terribly likely to be reliable - otherwise Miniscribe would have marked it as an 8438 in the first place.

We used to do the reverse sometimes: buy an 8438 and put it on a low-density MFM controller to make a very reliable 20MB drive system. It cost a bit more but because the 8438 was RLL certified, we already knew it was a particularly good drive, and by running it on an MFM controller we had a huge margin of safety. I can't remember ever seeing one of these under-stressed 8438s fail. Though we still saw working ST-225s from time to time up until the end of the century, we stopped meeting the 8438/8425 twins in working systems long before that.

By the way, these were one of the earlier 3½ inch drives to become common. Notice that the modest-looking capacity per platter is actually quite high when you consider that the discs are much smaller than was common at the time.

→ The 8425's absurdly flimsy power connector design. Standard nylon power plugs varied in size even more in those days than they do today, and getting a tight-fitting power cable out of an 8425 without breaking the PCB was often very difficult. The small white three-pin connector just above and to the left of it, by the way, is for a drive activity LED, and the light blue washer semi-visible through the gap between the power socket and the data cable edge connector is a shock mounting for the HDA. You get a better view of it in the larger picture above.

Performance0.16 or 0.20ReliabilityAA2
Data rate5 or 7.5 Mbit/secSpin rate3600 RPM
Seek time65msActuatorStepper
Platter capacity10.7MB or 16.45MBHeads2 or 4
AT drive type2Form3.5" half-height
MS-821210,7MB5 Mbit/secMFM
MS-842521.4MB5 Mbit/secMFM
MS-843832.7MB7.5 Mbit/secRLL