Date : Sat, 10 Jan 2004 10:25:48 +0000
From : Mike Tomlinson <mike@...>
Subject: Re: IDE Interface for BBC
In article <040110060610@...>, Jonathan Graham Harston
<jgh@...> writes
>I have a bazillion IDE drives on the shelf :)
I have, too, including a couple of 540Mb, a 640Mb and a 1.08Gb. Was
going to throw them out but will now be keeping them for this project :)
> I don't know how hard it is
>to find suitable SCSI/SASI drives for the Acorn card,
Depends on which Acorn card you're talking about. [I realise you - JGH
- probably know this, but am including it for completeness and so it
gets archived]
Hard disks for the BBC B used a SASI interface attached to the 1MHz bus,
and an Adaptec SASI-to-MFM converter board to which an MFM hard drive is
connected. I think Acorn's SASI card used all-TTL logic, and quite a
lot of it too, but I also had a Watford SASI card which reduced the chip
count to about 8 using PALs. The Adaptec converter board was about 4" x
6", was packed with chips, and had, if I remember right, an 8086 CPU and
its own firmware in ROM which in theory made it more powerful than the
machine it connected to.
I built my own hard disc for the Beeb years ago when I was lucky enough
to get hold of one of the Adaptec cards in a £1 bits bin at a radio
rally. Then I managed to get hold of the Watford 1MHz-SASI adapter and
it was a matter of assembling it all into a case with a power supply and
a 20Gb MFM drive stolen from an Amstrad 1640.
The simple SCSI card for the Master Domesday system sat in the space
inside the machine intended for an internal modem. I don't know if
anyone has successfully attached a SCSI disk to it.
Acorn's FileStores (Econet fileservers) came in two flavours. The basic
Filestore used floppy discs and a hard disc was an add-on option. The
earlier E01 had a 1MHz bus and used the same hard discs with SASI board
and Adaptec converter as were connected to the BBC B. The later E01S
used SCSI drives. The SCSI interface in the E01S I imagine would have
been very similar to the Master Domesday interface, especially as it was
based on the Master circuit.
>8-bit ADFS uses a 24-bit word (three bytes) to hold the sector number, a
nd
>expects 256 bytes in each sector. That makes the maximum 8-bit ADFS driv
e
>size as 4GB-1. 8-bit ADFS can access up to 4 hard drives, so a total
>amount of storage of 16GB.
Thanks. There's no support for partitioning, is there? Mind you, even
a 540Mb drive (reduced to 270Mb because of the 8-bitness of the
interface) would be ample, especially when you consider that the
original Acorn Winchester was 10Mb and came in a box bigger and heavier
than the Beeb itself :)
>I was thinking of making the FS software see if there was any extended R
AM
>available, on a byte-wide card such as Sprow's or a page-wide card in
>&FD00 and have the option of using that,
Perhaps it could also search for usable sideways RAM?
Rgds
Mike
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