Inside A DEC Hard Drive

A lot of technology from the not-so-distant past doesn’t resemble modern versions very much. For a case in point, look at the DEC RS08 disk drive meant to pair with a circa 1970 PDP-8. Paired with an RF08 controller, this was state of the art, holding 262K 12-bit words with a blistering access speed of almost 63K/second unless you were plugged into 50Hz AC when it was closer to 50K/second. [Uniservo] had the disk unit, but not the controller. Someone else had a controller, but no disk drive. So [Uniservo] is shipping the disk to its new owner in a move worthy of a Reeses’ Peanutbutter Cup. The problem? The disk is super fragile and shipping is risky, so he decided to remove the platter for separate packing. Good thing for us, because we get a peek inside.

The nickel-cobalt platter looks like a thick LP record with heads underneath. As you might guess from the data transfer specification, the motor was just a common AC motor that rotated the platter against the head.

It wasn’t unusual to wear out the platter and flip it over to use the other side. There’s no telling what a replacement platter would cost. The device was the first drive DEC developed themselves. Unlike a modern disk, the heads actually made contact with the platter.

Because the heads are on the surface, disassembly was tricky. There’s a chance that crud on the platter could scrape the surface if the platter were to move. Once the platter is out of the way, you can see the many heads. There were 128 data tracks and six timing tracks (three were spares). These mount on springs, and at first glance they look like Molex connectors with tiny coils within.

In a day when gigabytes can fit on your keychain and are virtually free, it is amazing to contemplate the engineering and cost that went into a device like this. You can only imagine what people in 50 years will think of our disk drives.

We enjoy the PDP-8, although our version doesn’t need a physical disk drive. If you ever wonder what all the lights and switches are for, we can help.