Re: SCSI on IIgs...

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

In article <area51-2204962128260001@pool056.max6.los-angeles.ca.dynip.alter.net>,
Adam Rumack <area51@earthlink.net> wrote:
> Do apple iigs's need a scsi adapter to use scsi drives?

Yes.  You need a SCSI interface card.  There are three reasonably
common SCSI cards:

1. The original Apple SCSI card.  This was released in 1986, and had a
   couple of ROM upgrades, the latest being in 1987.  It is the
   slowest of the three SCSI cards listed here, but it is also the
   cheapest.  With the final ROM revision, it supports SCSI hard drives
   and the original Apple CD-ROM drive (CDSC, probably also the CDSC+ and
   CD-150, but later models are dubious).

2. The Apple High-Speed SCSI card.  This was released in 1989 and has
   never needed a ROM upgrade.  It is considerably faster than the original
   card, because it is able to use DMA (Direct Memory Access) to transfer
   data to and from the computer's memory.  In theory, it can transfer
   data as fast as 1 megabyte per second under ideal conditions on a IIgs.
   The Apple High-Speed card supports SCSI hard drives and the
   original Apple CD-ROM drive models, as above.

   It will also work with some other SCSI devices, such as Apple's
   CD-300, 40SC Tape Backup drive and the original scanner, but there
   are limitations (e.g. no audio support and odd behaviour with the
   CD-300; a third-party audio driver is available).

   Both Apple cards can support additional devices under GS/OS if a driver
   is written to support them.  There are a few third-party drivers
   available.  It is also possible to access any SCSI device (even
   ones not supported by the firmware, I think) directly under ProDOS-8,
   given enough documentation on the device and a copy of the SCSI-1 and
   SCSI-2 standards.

3. The RamFast SCSI card, from Sequential Systems (originally sold by
   CV Technologies).  This is the fastest of the three cards.  Like the
   Apple High-Speed SCSI card, it supports DMA.  It also has cache RAM
   on the card, which substantially speeds up disk accesses, especially
   under ProDOS-8.  With GS/OS, the RamFast performs somewhat better than
   an Apple High-Speed card, but the difference isn't as noticeable with
   a fast hard drive.

   The RamFast is the most expensive of the three cards, but it is the
   only one which is still being sold and supported.  It supports the
   widest range of devices, and has all the support built into the ROM
   on the card (and/or the GS/OS driver).  It has had frequent ROM upgrades
   over the years to support additional devices and to fix bugs.

   There are two main versions of the RamFast: the "revision C" and
   the "revision D".  The "D" only works in a IIgs, while the "C" will
   also work in a IIe.  The "D" has up to 1 megabyte of cache RAM,
   while the "C" only supports 256KB.

   There are a few catches with the RamFast:

   i.  It doesn't work with some very new SCSI hard drives, such as
       the Quantum Fireball, which require the host to provide a SCSI
       ID.  The RamFast doesn't have a SCSI ID (which allows it to
       support eight peripherals instead of seven).

   ii. It doesn't work with disk-based drivers written for Apple SCSI
       cards, or with many utility programs which are specific to the
       Apple cards.  (This is not a major problem, because the RamFast's
       on-card ROM contains most of the utility functions you'll ever
       need).

   iii.The RamFast cannot share a SCSI bus with another computer.  (This
       is rarely needed, and has to be done carefully to avoid problems.)

My first SCSI card was the original Apple one, and I have subsequently
bought two Apple High-Speed cards.  I've used them all with the
original Apple CD-ROM drive, a variety of SCSI hard drives (including
a Quantum Trailblazer and a SyQuest SQ44) and a clone of an Apple CD-300.

I even had a 9 Gigabyte drive connected to my computer the other day
(unfortunately, the drive was faulty so I don't know if it would have
actually worked...)


There are some other rarer SCSI cards around.  One that immediately
comes to mind is the CML SCSI card.  This card is rather unusual,
because it has jumpers to set the partitioning of the drive.  It only
supports SCSI hard drives (and possibly only CML SCSI drives), and its
partitioning scheme is incompatible with all other SCSI cards.  (All
three of the cards above use the same partitioning scheme, which is
also compatible with the Macintosh.)

The CML card does have a useful feature: it can be used to share a
hard drive between multiple computers, as long you set all the cards
up correctly.  This is only safe if the shared partition is configured
as read-only from all computers.

(An acquaintance of mine had his CML "network" set up with read/write
access from all computers, and complained that he was seeing bits of
subdirectories appearing in the middle of his AppleWorks
spreadsheets!)
-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand