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February 8th, 2014:

The Original Hard Disk

I know I have an original Bernoulli Box 10 MB cartridge somewhere. I saved one because I was sure that nobody would believe me when I waved this huge slab of plastic at them and said, “This holds 10 MB.” I think I was right. I won’t know until I find it. So I looked…

…and I found something else instead. See the photo above. Anybody recognize it? It’s part of one of the earliest hard drives in computer history. It’s such an old hard drive that it wasn’t even a hard drive. No. It was main memory.

I honestly don’t remember who manufactured it, though Sperry-Univac sounds familiar. (I threw out the case when we left Rochester in 1985.) I bought it at a hamfest for a couple of bucks just for curiosity’s sake; the old guy I bought it from said it was a hard disk, and I was skeptical. He was right, and it was probably fifteen years until Google allowed me to look for an explanation. I took the case apart and found a motor, a fairly heavy aluminum disk coated on one face with red iron oxide, and the assembly above, which has 160 magnetic heads in eight spiral groups. Roughly half the heads look like gray ferrite, and the other half like white ceramic. I’m guessing that the gray heads are write heads, and the white heads are read heads. (It could be the other way around.) The whole assembly is 9″ in diameter; the magnetic disk is 8″ with the outer 2 1/4″ coated with oxide.

So what we have here is a device that imposes 80 tracks on 2 1/4″ of oxide. The number of bits on each track remains a mystery. 1000? 2000? Somewhere in there, which suggests a total of 100,000 or perhaps 120,000 bits, which would provide about 16KB. This was RAM, not mass storage. The principle is basically the same as the magnetic drum memory systems that IBM sold with its vacuum tube machines like the 650. There were no moving parts other than the disk itself, and you can spin a disk faster than you can spin a drum. I’m guessing that the magnetic disk units like mine filled the (narrow) gap between magnetic drums and core memory. I’ve seen writeups indicating that magnetic disk storage was used for swap storage as late as the PDP 11/45 in 1972. The unit I have seemed a lot older than that.

One of the problems in researching a unit like this is that “hard disk” and “magnetic disk” have other, more modern meanings. So what needles may be are lost in the titanic haypile of newer technologies. If any of you know anything more about the technology send me a quick description or links, and I’ll post them in a future entry.

I had 8″ floppies in my first CP/M machine, and 5″ floppies in all my PCs until the 90s. I used SyQuest cartridge hard drives for years after my 1986-1992 romance with Bernoulli Box drives, which drove me nuts with their constant indexing of heads across the medium. (Tick…tick…tick…) The SyQuest cartridges spun fast and died young. There followed three generations of Zip drives, culminating in the monumentally awful Jaz. It was only in 2004 that I set aside moving parts in my removable storage, and began using thumb drives. I’ve had an SSD on my main system for eighteen months, and will be putting them in most of my lab machines as well, spurred by the need to get XP out of daily use here.

It’s sobering to remember: We’ve been spinning magnetic disks for what may well be sixty years now. We’re still spinning them, and we will be for another ten years or so at least. What other computer technology has been in wide use for that many years? Tape–maybe. That’s the end of my list.

Damn. That’s a lot of angular momentum. Will I miss spinning disks when they’re gona entirely?

Hah. Guess.