Re: regular Apple SCSI card question

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

Supertimer <supertimer@aol.com> wrote:

> "Jason Whorton" <jason@microxl.com> wrote:
> 
> >Can I find a terminator that is DB-25 on both sides?  Does anyone have
> >any tips on what I should do?
> 
> You can find such terminators at most computer stores.  However,
> I think the Apple II SCSI card is already terminated.

Not the original one.  The rules for this card:

1. If you are connecting a single drive, then there must be a single
terminator at the end of the chain (piggybacked on the drive, or
internal to the drive).

2. If you are connecting two or more drives, then there must be two
terminators: one in the same position as above, and the other one at the
computer end of the chain, either a pass-through terminator between the
computer and first drive, or internal termination on the first drive.

I've used a 50-pin pass through terminator in this configuration without
any problems.  You shouldn't need a 25-pin one.

> >    Also, if anyone has an Apple High Speed SCSI card for sale, please
> >e-mail me.
> 
> The HS card is mainly useful for removable media like Zips, Jazzes,
> and CD-ROM drives.  It is an excellent card, but if you are just
> going to use non-removable hard drives of not too large sizes,
> the regular Rev. C card is ok.  The other advantage of the HS card,
> if I recall, is that it supports more partitions under GS/OS.

Nope.  The big differences are for ProDOS-8: the original card can only
support a total of 7 partitions (over all connected drives), while the
high-speed one can do something like 110 (in theory).  The problems with
removable devices also apply only under ProDOS-8.

GS/OS support is identical for the two cards - same drivers.  The limit
(imposed by GS/OS itself) is 63 partitions, distributed over all drives
connected to all Apple SCSI cards (of either type).

The only practical difference between the cards under GS/OS is the
speed.  The High-Speed card is _much_ faster than the original one,
given the right circumstances.  The difference is much less noticeable
under ProDOS-8, since the overhead of issuing SCSI commands for each
block accessed pretty much wipes out the transfer rate advantage.

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand