Prototype IBM DemiDiskette drive

[Chuck Guzis]

Nice to see that someone managed to hang onto one of these.

To offer a bit more information on the "battle of the shirt-pocket
floppy", IBM wasn't competing just against the Sony 3.5" format, but
also the Dysan/Shugart 3.25" format, which, as is the IBM prototype,
more in the 5.25" true "floppy" format.

The field is littered with casualties.   Amstrad used the 3.0 inch CF
format for a time; Zenith had the "shrunken" 2.5" size....etc. etc.

All in all, I think the right format won the battle--3.5" floppies are
physically pretty rugged.

Not that any of this matters today. :)

--Chuck





On 08/22/2018 06:28 AM, Eric Schlaepfer via cctalk wrote:
> Yesterday I dug out my prototype IBM DemiDiskette drive and took some
> photos: https://twitter.com/TubeTimeUS/status/1032066215647166464. It
> caused a bit of interest on Twitter so I figured some of you here may also
> like seeing it.
> 
> I don't really know a whole lot about it other than what my grandfather
> told me (he worked on the team that developed it). Dates on the remaining
> paperwork go from December 1979 through August 1980. It was supposed to be
> a very low cost drive for the microcomputer market (target price IIRC was
> <$100). Although it was originally developed by a team working at IBM
> Austin, it was handed off to a different team apparently working out of
> Rochester.
> 
> The disk capacity was not very large--I don't remember the exact number but
> it was probably around 100K or less.
> 
> A few interesting observations:
> 
> * The stepper motor uses a spiral cam to convert rotation into linear
> motion to drive the head.
> * It is a single-sided drive.
> * A microswitch senses the presence of the disk instead of an optical pair.
> * There is no write protect notch or sensor.
> * There is no index sensor.
> * The spindle drive motor is a DC brushed motor with an encoder wheel for
> speed control.
> * Not shown in the pics, but the plastic "spot welds" holding the vinyl
> jackets on the disks are intentionally widely spaced making the cookie
> easier to remove for analysis.
> 
> It's not really something you get to see every day, that's for sure...