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

From: Jules Richardson <julesrichardsonuk_at_yahoo.co.uk>
Date: Thu Dec 11 06:17:17 2003

On Wed, 2003-12-10 at 23:50, Tony Duell wrote:
> Some controller have links to enable/disable precompensation. The Adaptec
> ACB4000 (I mention that one, since I have an ACW on the bench at the
> moment, so the details are stuck in my brain)

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

> 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.

>> Having one drive per classic doesn't help a) at all, but reliable
>> drives in the order of 1GB or so can be found for free and are
>> likely to keep
>
> The simplest hardware would seem to take 2-3Gbytes for a maximum-size
> ST506 image. Most will be a lot smaller than that. I think 20-40Gbyte
> IDE drives are pretty cheap now....

Presumably there's nothing to stop data being compressed/decompressed at
the 'new' hard drive level, providing the emulator is fast enough to do
this. Unless your ST506 (for the sake of argument) drive contained a
single huge compressed file originally, compression level should be
reasonably good.

>> (I'd still much rather use SCSI drives as that's what I have
>> spares of - I don't keep IDE drives lying around)
>
> I don't have either 'spare'. It really comes down to which makes the
> hardware interface easier. I'd like to try DMA (see the other message)
> this is not too hard on a SCSI drive, I think it's OK on most
> modern-ish IDE drives.

Fair call. The shorter cable lengths of IDE *might* be a problem with
mounting in some machines I suppose, but it isn't a biggie. Getting
something that works for the first version is better than nothing :-)

>> Point c) about backup can be rethought. All the interface needs is
>> *some* way of getting data out of it (and back into it, presumably :)
>
> A really kludgy way to do this is to pull the drive from the
> emulator, cable it up to a PC, and copy the image over using dd
> or something. Not elegant, but it'll work (remember the data on
> the modern drive is stored in normal sectors on said drive, so
> a PC can read it, even if it can't make sense of it).

Absolutely. That's how I back up some of my classics with SCSI drives at
the moment :)
It, presumably, would not be difficult to stick a serial port on this
thing for some sort of rudimentary control; there are likely parameters
which it would be handy to be able to set up remotely without delving
inside the classic machine hosting the emulator anyway. Transferring
2-3GB across a serial line isn't really viable (serveral days to
transfer!) but for the more common classic drives in the 10-30MB range I
imagine it's viable.

cheers

Jules
Received on Thu Dec 11 2003 - 06:17:17 GMT