Re: SCSI Interface for A2GS

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

Mark Cummings <NOTfigjams@primus.com.au> wrote:

> Forget about burning, besides the lack of any CR-R software, I doubt the GS
> could supply enough data even if accelerated.

You might be surprised.  On a IIgs, the Apple High-Speed SCSI card can
support a sustained transfer rate between drive and memory nearly as
fast as the bus interface (approaching 1 MB per second), using specially
written software.

Apple did a demonstration when the card was released which was doing
full motion video by using DMA to transfer data to the Super Hi-res
screen from a hard drive.  I don't recall the exact frame rate, but I
think it was 30 frames per second, which means that the card was
transferring 960 KB/s.

Doing a 1x data CD burn requires a sustained rate of 150 KB/s.  (Audio
CD is about 172 KB/s.)

The difficulty is that you also need to factor in transfers from the
hard drive to the computer, unless you only wanted to burn a CD session
no larger than the RAM, or use packet writing.

If your source material was on a SCSI hard drive on the same bus, a
distinct possibility would be to implement a direct device to device
SCSI data transfer, as long as the CD burning protocol can support this
(I believe it can, as Toast makes use of this feature).


I don't know how the RamFast would cope.  It doesn't have a SmartPort
firmware interface, which probably means that there is no way for an
application to issue arbitrary SCSI commands, which pretty much rules
out communicating with any device not supported by the firmware, or
using special features of devices which are only supported in a generic
manner.

Speed might also be an issue.  It may be optimised for high performance
reads, but be slower for writes.