[Coco] Diskettes

[Steven Hirsch]

On Tue, 28 Jun 2011, Willard Goosey wrote:

> On Mon, Jun 27, 2011 at 09:30:12PM -0500, Steve Ostrom wrote:
>> I found a set of eight diskettes that I have never seen before.  They
>> are 3M DEC RX 50 disks.  A Google search says the DEC RX 50 drives were
>> very unusual, with DEC trying to cram a lot of data on one diskette
>> using odd parameters.
>
> The RX50 drive is very weird.  It's quad density, 80-track, but I don't
> quite know rather to describe it as single-sided or double-sided....
>
> It looks like 2 half-height drives in one full-height package but it's a
> single drive, sharing (IIRC one drive motor and one head-moving servo?
> that runs both "drives")
>
>> From what I understand, it *pretends* to be a 720K double-sided drive,
> by combining 2 qd single-sided disks!  Disks were usually used in pairs,
> one as "side 1" and one as "side 2".  The user had to be careful to put
> the correct disks in the correct slots.
>
> I've got one, salvaged out of a Rainbow or a Pro-350.  I tested it on my
> CoCo but without proper 80-track floppies it didn't work so well.

Cool.  I have one of those drives (definitely pulled from a Rainbow).  I 
had no idea that it logically combined the two diskettes!  DEC always HAD 
to be different.  Back in the days when CD drives used caddies, DEC even 
spent the effort to create their own, incompatible, form-factor.

> Gods only know what those disks might have on them.  The Rainbow was a
> CP/M and MS-DOS machine, the Pro-3x0 line were PDP-11's, I've seen
> regular PDPs with an RX50, and I think I once read that some VAXen want
> to load CPU microcode off an RX50 on power-up.  I'm not sure where the
> old-school DECheads hang out on the Net, but they'd probably be glad to
> see those disks.

The Rainbow (not sure about the Pro-xx) was notorious for not shipping 
with a low-level disk format utility!  They based the business model on 
selling pre-formatted media to customers at inflated prices.  Guess how 
long it took for someone clever to reverse-engineer the low-level scheme 
and release a free utility?

Steve


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