Re: SCSI Rev?

[dempson@swell.actrix.gen.nz (David Empson)]

In article <ratkinso.11.758227764@scholia.wbme.jhu.edu> ratkinso@scholia.wbme.jhu.edu (Ron Atkinson) writes:
> What's the difference between the Apple SCSI cards?
> 
> Rev A
>     B
>     C
>     High Speed

There are two Apple SCSI cards: the original one (made in 1986) and
the High-Speed one (made in 1989).

The original card went through three ROM versions: "revision A",
"revision B" and "revision C".  I had a "revision A" ROM when I bought
my card, which I later upgraded to a "revision C".

I don't recall seeing a full list of the changes between the revisions,
but I can remember a couple of them:

- Rev B or C changed one of the SmartPort Control Calls from "Format"
to "Eject" (for compatibility with other devices).  This call is now
documented as "eject" in all SmartPort references.  If you use this
call on the Rev A ROM, you will format your hard drive!

- Rev C added support for CD-ROM drives.

Rev C is required to use the card from GS/OS.


The High-Speed SCSI card has never had a ROM revision.  I think it
supports Tape drives as well as hard drives and CD-ROM drives (via the
firmware, i.e. from ProDOS-8).  [GS/OS supports tape drives and
scanners with either SCSI card, because it bypasses the firmware.]
It also knows about removable hard drives (like the SyQuest) - the
original SCSI card doesn't realise you've ejected a cartridge and can
destroy disks if you put a different cartridge in without rebooting.

The main advantage the High-Speed card is that it can use DMA (Direct
Memory Access), which increases the I/O speed.  It also supports
special data streaming commands which, when combined with DMA, result
in data transfer rates of up to 512k per second on a IIe or 1MB per
second on a IIgs.  Even with normal data accesses, there is a
noticeable difference in speed between the two cards.

The High-Speed card requires a 65C02 (i.e. enhanced IIe) or a IIgs.

At the SmartPort call level, the cards are very compatible.  There are
a few obscure calls which are not supported by the High-Speed card,
and the method for making a generic SCSI call has changed (for the
better).  The original SCSI card had several data tables you could
access in its RAM, but these are not available on the High-Speed card
(most of the information is available by making SmartPort or SCSI
calls anyway).
-- 
David Empson                                                               
dempson@swell.actrix.gen.nz                                                
Snail mail: P.O. Box 27-103, Wellington, New Zealand