Re: CMS SCSI

[David.Empson@bbs.actrix.gen.nz]

In article <bc00147@pro-gumbo.cts.com> tgeer@pro-gumbo.cts.com (System Administrator) writes:
> In <22357@ucdavis.ucdavis.edu>
> mock@madrone.eecs.ucdavis.edu (Kenrick Mock) writes:
> 
> >Hehe, you got it...I still have TWO old CMS drives.  I've done away
> >with that crummy CMS II card though.  The thing is one of the slowest
> >SCSI cards I've seen.  For anyone with a CMS II card and drives, I
> >recommend you scrap it and buy a RAMFast instead :)
> 
> Not entirely true.  While the older ROM versions of the CMS card were indeed
> sloooow, the newest revision (3-1-90) is fairly zippy.  I have since moved
> to the Apple DMA High-Speed SCSI Card and did some speed comparisons.  The
> new ROM CMS card is only marginally slower than the Apple card with DMA
> turned on.

I did a similar comparison between the original Apple SCSI card and
the DMA SCSI card.  For typical operations (under ProDOS 8), there
isn't much difference (10% to 40% increase in transfer rate).
However, under GS/OS with multiple-block transfers (and a fast enough
hard drive), the DMA SCSI card starts to show its worth. With specially
written software that takes direct control of the DMA process, it is
possible to get transfer rates of up to 1 megabyte per second.

I believe Apple did a demo using the card, in which DMA was used to
transfer data directly from the hard drive to the super hires screen.
It was able to manage 30 full-screen updates per second (960 kb per sec).

Try that with the processor!

> I switched to the Apple card mainly for compatibility reasons.
> It doesn't keep up with the RAMFast in raw speed, but unlike the RAMFast,
> how often do you see a post about someone having trouble with their Apple
> card?  I'll answer that: never.

Agreed!  The HS SCSI card hasn't had a single ROM upgrade since it was
released in 1990.  The old Apple SCSI card had two revisions, but its
software was written in the infancy of Apple's dabbling with SCSI, so
there were bound to be problems.

Give me floppy-based device drivers any day.  I can do without monthly
ROM upgrades (I do enough of that with my own software at work).
-- 
David Empson

Internet: David.Empson@bbs.actrix.gen.nz    EMPSON_D@kosmos.wcc.govt.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand