Disk hardware emulation, was Re: Grandfather system RTE6/VM?

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Thu Dec 11 19:18:24 2003

> Oh, that reminds me - I came across another ACW owner last night.
> Waiting to hear what (if any) docs / software he has for it.

Interesting. I have most of the ssential docs (user guide, service
manual, nearly a _complete_ schematic) now, though.

>
> > 4) With a few slight hardware changes (specifically related to the 'head'
> > selection and index pulse), the emulator could be connected to the
> > original ST506 _drive_ and make an image copy of it onto the modern disk.
> > This would be useful for machines that can't do a low-level format
> > (again, the HP9133 springs to mind) since such an image copy would copy
> > the low-level format too. The modern hard disk could then be connected to
> > a normal emulator and used to replace the ST506 drive in the classic
> > computer.
>
> That, I think, is a must, compared to having to design something else
> entirely to read the data off the drive in the first place. And as you
> say, hopefully it isn't too complex to achieve.

It looks to be very straightforward to do this. The frst thing to do,
though, is to get the data capture circuit actually working. Then we can
figure out how to link it to the controller and/or drive.

> Presumably there's nothing to stop data being compressed/decompressed at
> the 'new' hard drive level, providing the emulator is fast enough to do

I mentioned this a few messages back. Yes, it can be done. It becomes a
trade-off between the transfer time for the entire cylinder image (you
want to compress each cylinder separately, so you can just
compress/decompress that as you move data between the emulator RAM and
the modern drive) and the time taken to compress/decompress it. If you
_don't_ use compression, then you can do a relatively simple DMA trick
between the emulator RAM (which has an address counter anyway) and the
modern drive. This means you need almost no CPU power to control the
emulator, as that CPU isn't involved in data transfers.

> this. Unless your ST506 (for the sake of argument) drive contained a
> single huge compressed file originally, compression level should be
> reasonably good.

It should be good anyway. The bitstream image is a lot larger than the
data it encodes, so you should be able to compress it rather nicely...

-tony
Received on Thu Dec 11 2003 - 19:18:24 GMT