1970 way stripping a disk drive

Nowadays, mass storage for computers is quite simple. This is either using a rotating disk otherwise it is a difficult condition. There are also a few holdouts using tape, but compared to what it was before, the tape is all dead. But it wasn’t so long ago that there were so many types of mass storage. Tapes, discs, drums, punched cards, paper tapes and even strangers. Probably none was as weird as the IBM 2321 data cell drive – what IBM internally calls MARS.

You may ask, what is a data cell? A data cell was a mass storage device of IBM in 1964 that could store about 400 megabytes using a magnetic strip that looked like about a foot of photographic film. The strips are inside a drum that can be rotated. When you need a record, the drum will turn the strip you need into the work piece and an automated process will remove the strip in question, wrap it around a reed / right head, and then return it when it’s done.

Needless to say, these were not caught. Tape drives were good for most things, and disk drives would soon be cheaper, which would destroy the 2321 as a historical curiosity.

Given the limitations of the day, the solution was clever. Each strip was two inches wide and 13 inches long. Each drum had 200 strips and a 20-track head that could go to one of five locations, meaning that each strip contained 100 tracks of data. For high storage requirements, you can connect multiple devices together.

The drum was like a very long slide projector that carried a magnetic strip instead of an optical slide.

If you look at the pictures, it’s hard to see how they fit into 200 strip drums. You should see the drawing from the IBM manual that makes it clear. The drum is really made up of 10 cells. Each cell has two sub-cells of 10 strips. Body layout is like an old carousel slide projector. The strips are like very thin slices of pie and the machine sucks a certain strip on a certain reed right head.

Of course, this sounds like a rub goldberg, but consider it. Similar to the IBM disk drive of that day, less than 1/50 of the data cell can hold. If you load a control unit with eight drums, it will be equivalent to more than 440 IBM2311 disk drives. Don’t forget, you will also need more than 50 controllers for disk drives. Disk drives, of course, were faster, but not by much. Access time of 2311 was 85 mS as opposed to data cell cloaking around 600 mS is the worst-case although if they and the strips are aligned it can be as fast as 95 mS.

Tape cartridge for IBM 3850

If you think these were noises, you are right. They also took a special oil to lubricate all the work. Apparently [Nerding] One day I had the opportunity to work with one of them. The computer was giving and receiving credit approvals and it was shutting down. It was found that sharing these data cells is risky. One program can move the drum and another program can move it again if the first one reads if the programs enter the opposite side of the drum.

IBM has created 3850 which can store up to 472 GB on IBM System / 370. It was a very similar idea, but the magnetic tape was not in the strip but in the small cartridge that held 50 MB each. It was more like an automatic tape machine than a disk drive, but it still shows that the disks take some time to completely pass the tape.

Diagram of Reed / Right Head of IBM

We have a light urge to build a working replica. Of course, aligning at 1.8 degrees involves some subtlety, but if you build a 3D printer or CNC machine, that number has a familiar ring. A typical stepper motor can make 200 full steps per revolution. Go to the figure. The other thing that will be difficult to do properly is to manage the weak film. The film itself, according to IBM, is 0.005 inches thick. Still, you think you can figure something out.

We will decide for an emulator, especially if it is a graphical simulation. While we may have IBM to thank for popularizing tape storage, we can thank Bing Crossby for making audiotape a thing.

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