compucolor

[Jim Battle]

Vintage Computer Festival wrote:

> On Sat, 7 May 2005, Jim Battle wrote:
> 
> 
...
> Mine produced smoke too :(  Where did yours smoke from?  I want to get
> mine working again.  It seemed to have come from the CRT section.  I'll
> bet I have a smoked cap somewhere.

I didn't see any smoke.  The previous owner reported it, so it was just 
speculation on my part that it was dust cooking off the CRT neck.

A very common problem reported is that the switching power supply 
sometimes wouldn't start oscillating and it would result in a cooked 
machine.

>>Disks couldn't be formatted using other computers because of the hokey
>>(although dirt cheap) disk interface.  ....
>>Anyway, ISC took advantage of an undocumented
>>test mode of the chip to drive the serial port at 8x speed.  The disk
>>looks like a high speed serial channel and the data is simply
>>conditioned and drives the r/w head of the disk drive.> 
> 
> Way cool!  Not as cool as the Apple Disk ][ interface though :)

I have to respect both, for different reasons.  The compucolor design 
(given the fact that the RS-232 chip was already there) cost them one 
jellybean chip -- they mux/demux the data to the RS-232 port or the disk 
drive using a few sections of a tristate buffer.  The apple II design by 
comparison was 10x more complicated.  The apple II design also had super 
critical timing requirements of the driver code but the compucolor 
design didn't.  On the flip side, the apple design had better density 
and was incredibly flexible.  So I respect the compucolor for minimalism 
and the apple design on esthetics.

It has been reported that originally the compulor was designed to store 
to an 8-track cart, but then they ECO'd it to drive a floppy disk 
instead.  The disk allocation is very simple and perhaps derives from 
its original tape cart implementation.  Files are contiguously allocated 
on the disk and files are kept packed.  Files can only be added to the 
end and if you delete a file in the middle, all the later files get 
shuffled down.  And in order to make it go faster, they use the 4K of 
video RAM to buffer multiple sectors during the shuffling.