With an utter dearth of information about "MMi" (the company mentioned on the label affixed to my HyperDrive20 drive mechanism), I decided to write GCC. GCC currently makes laser printers (and has for many, many years) but prior to that they made HyperDrives (and prior to the Hyperdrive they were into video games). Donna from GCC was kind enough to provide us with the following response today:

This is what I found.
mmi was *not* a drive manufacturer, they were an IC manufacturer, MiniScribe

was the drive vendor, the original hyper drive products for Mac plus didn't

not change the processor type, in fact it clipped onto the processor we did

a product for the Mac se called 'hypercharger 020' which upgraded the

processor from a 68000 to 68020. The MMI that is well known is 'monolithic

memories inc' they did earlier devices called PALs P)rogrammable (A)rray

(L)ogicwe we were a very large customer of theirs in the early days

PALs at the time allowed use to produce more compact designs (as well as

hide elements of the design from copiers/counterfitters)

This came from our engineering department.

Click to expand...

So while she does not appear to know the specific model, she does indicate the drive mechanism is MiniScribe. She does refer to the Mac Plus and a Plus related accelerator product, which came later than the HyperDrive 20. But I am assuming that her comments about MiniScribe also cover the hard drive mechanisms used in the early HyperDrive 10 and 20 models.