SD Card disk drive for C-64?

Jim Brain brain at
Sat Jan 23 19:33:54 CST 2016

On 1/23/2016 7:15 PM, drlegendre . wrote:
> " I am saying don't make a permanent hardware change to a 1541 that
> does not have the switches unless you really want it to be permanent
> because there is a software method of assigning drives that is good enough
> most of the time.  BUT if you must make it permanent and you don't have the
> external switches, consider adding some form of external switch so you
> don't ever have to open the case again to put it back to the default."
> Well then, we're having a major agreement. ;-)
> The device ID switch is the ultimate fix for Commodore drives, and I'm
> really not sure why CBM didn't incorporate one into the design - at least
> from the 1540 on upwards. Can't have cost much to add a discretely located
> access hole (or a knock-out) in the case, along with a 2-place DIP switch
> for controlling device ID.
But, they did.  The 1541-II, 71, and the 81 have switches.

I would disagree on your point that Commodore should have made it part 
of the design...

Let's travel back in time.

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).

Tramiel is mad, and the drive doesn;t sell terribly well at first.

When the VIC-20 comes out, the drive is just marketing materials. Why 
would someone want a business storage system for a home computer 
basically built because Jack needs to unload a bunch of VIC-I ICs that 
he can't sell to video game firms?

But, people asked for it, and CBM delivered, taking Peddles IEEE design, 
ditching the IEEE cabling (Jack: "Get OFF that bus", as the cables from 
Belden/Beldin(sp?) cost a mint and supplies had been spotty at times).  
The unit is retooled to use 1 drive, 1 CPU (and in the process the 
changes introduce the fabled "save with replace" bug.  Enter the 1540

But, the designers put little jumper pads on the drive to set dev 
number, as they were very sure most people would never buy two of them.

Then the 64.  Paddle's ColorPET design loses out to a hacked VIC-20, 
which became the 64

Now the drive seems more useful, and can be made more cheaply.  As well, 
other units in the marketplace have drives, so it is a competitive 
need.  All is well, though, as the 1540 is already in production. Dump 
some gray tan/gray colorant in the injection mold machines, and you're 
done.  That's classic Jack.

The 1540 has a problem though.  The bit banging protocol (introduced 
late in the 1540 design cycle after it was determined that the VIC shift 
register has issues) fails on the 64.  high/low times are 20uS/20uS, and 
sometimes the CPU is stopped for 50uS on the 64. Enter the 1541.  No 
changes except the ROM, which slows down sends from the drive to the 64 
to 60/60uS clock.  Jack is done.  He doesn't care if people buy them per 
se, just that the drive is there so he can tout it being there as he 
competes with the Apples and Ataris.

So, at the time, with the drive being as much as the computer, no one 
thought people would buy more than 1, and thus no need to pay for extra 
parts (switches) and changing the molds.

With the C128 and the case redesigns, people were buying multiple 
drives, and it was a selling point, so the switches made their appearance.


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