Another disk imaging project

[Tony Duell]

> 
> there are a few contraptions out there by which you
> can connect a CF or SD card to a Commodore 64,
> presumably an IDE drive too. Try ide64.org for

Yes, from what I rememebr, a CF card can be made to look very much like 
an IDE drive.

> starters. There was another one on Epay recently,
> which I think used an MMC/SD card.
>  The notion of adding such a device to an old puter
> has intrigued me also. Old RLL/MFM drives are a waste
> of time IMHO, and new IDE drives probably won't work,
> provided you even had an IDE interface (they do exist

The IDE interface is very simple (the IDE card in this computer is about 
10 TTL chips and a PAL). It should be possible to link an IDE drive to 
just about any old computer, as the drive (AFAIK) includes a data buffer 
RAM, it shouldn't matter if the host can't keep up with the data rate.

I will admit I've not tried it, though.

I suspect the main problem is writing the necessary drivers and getting 
the OS to recognise the new drive

To take my favourite classic, the PERQ. It would be fairly easy to add an
IDE drive interface on an OIO (Optional I/O) card. It would also be not
too hard to write a program to transfer files between the main
(ST506-interfaced) drive and the IDE drive, that is to use the IDE drive
as a sort of backing store. It would be a _lot_ harder to get a PERQ to
use an IDE drive as the main hard disk. 

> for XT class machines, but most of mine have
> proprietary buses). 
>  I know this is a broad question, but to what degree
> can an FPGA take the place of early custom ic's? Say

An FPGA is bascially what it says it is. A chip containing arbitrary 
logic gates (you define the functions when you program the chip) and 
flip-flops. Programming also defines the internal connections between the 
gates.

You cna make just about any digital function using an FPGA, including, of 
course, procerssors. If you want to replace an existing chip, of course 
it's unlikely you'll be able to make a drop-in replacement (you can't 
assign power pins where you like, often an FPGA has dedicated clock 
inputs, etc). 

Another problem is working out the schematic/VHDL 'program' that 
represents the chip you want to replace. Particularly for custom chips 
where the full specs may well not be available

And another problem is that, no matter waht the manufacturers will have 
you believe, every FPGA I've seen has interesting quirks. I suspect that 
if you took the schemaitcs of a TTL-based minicomputer, put them into a 
schematics capture program and turned the result into an FPGA program, 
the resulting FPGA would _not_ correctly emulate the original minicomputer.

-tony