SD Card disk drive for C-64?

Mike Stein mhs.stein at
Sat Jan 23 23:53:32 CST 2016

----- Original Message ----- 
From: "Jim Brain" <brain at>
To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at>
Sent: Saturday, January 23, 2016 10:28 PM
Subject: Re: SD Card disk drive for C-64?

> On 1/23/2016 8:58 PM, Eric Christopherson wrote:
>> On Sat, Jan 23, 2016, Jim Brain wrote:

... snippage

>>> After the PET intro, Peddle designs a drive, a beast of a device, with 2
>>> CPUs and it costs a fortune.  Peddle is convinced a smart drive is best, and
>>> the delay allows other manufactures to create "dumb" drive options (saw one
>>> at World of Commodore, forgot the name).
>> How did these dumb drives interface with the computer at a software
>> level? I'd think a DOS would need to be loaded somehow.
> The one I saw at the WoC was a 8" drive connected to a PSU and the cable 
> attached to a small PCB that replaced the editor ROM in the PET.  THe 
> PCB mapped a controller into the address space and the editor ROM was 
> patched to support a DOS.
> It was an interesting setup.  Mike N (of had the unit. Steve 
> Gray on here was there too and could provide more details.
> Jim
I was the third guy at Mike's WoC booth trying to help figure out why it wasn't working initially; took a while for one of us to notice that the PET we were using was a different revision than the one Mike used at home and it had to be connected slightly differently. I also made a cable to try using a 5.25HD drive instead of the 8" but we (I) didn't have enough time to get that working completely.

The device in question is a CGRS Microtech PEDisk II and just like most systems it has a boot ROM which provides some low level functions including the loading of a DOS from disk, which in turn is accessed with a set of 'wedge' commands.

When I asked here recently about cloning a PCB this is the one I had in mind, but we'll need a schematic anyway sooner or later; Mike's already done a heck of a job reverse-engineering the software.

More info here:


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