Re: Using 20SC with //GS?

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

Marvin Miller <marvinmiller@hotmail.com> wrote:

> What sounded simple is now getting complex! Perhaps I should give you
> the complete scenario as it looks like there might be issues
> looming....
> 
> I need a SCSI controller for my ROM 03 //gs.
> I have two Quantum Fireball TM's (2.1gig) that are NT formatted that I
> want to install into two cases (there seems to be no issue with the
> cases, but maybe with the drives?)
> 
> In this //gs will be a 6 meg AE memory card and a ZipGS initally
> running at 7Mhz and soon to pushed to at least 10Mhz.

I can see an immediate problem here:

Quantum Fireball drives will not work at all with a RamFast SCSI card.

You must therefore use an Apple SCSI card.  The original Apple SCSI card
is slow and severely limits the number of partitions under ProDOS-8 (a
maximum of seven, spread over all mounted SCSI devices), so the Apple
High-Speed SCSI card is your best option (it will give you at least
seven partitions, and perhaps as many as eleven, depending on what cards
are in the other slots and which internal ports are enabled).

Using the Apple SCSI card raises another problem: if you have a memory
expansion card larger than 4 MB, it cannot use DMA to access memory
beyond the 4 MB point.  With some large cards, it is safe to leave DMA
enabled, and you will only get slower performance with the "extra" RAM.
With other cards, you will get memory corruption, because the DMA ends
up going to the wrong area on the card, and the only option is to
disable DMA on the SCSI card.  This causes a major performance hit.

With some cards that support more than 4 MB, this problem comes up even
if the card only has 4 MB (or less) installed.  It depends on how the
card decodes memory addresses.

In some cases you might be able to avoid problems by setting up a large
enough /RAM5 volume to permanently reserve the memory beyond the 4 MB
limit, i.e. at least 2 MB in the case of a 6 MB card.

The RamFast is able to work around these issue with some but not all
large memory expansion cards: it can do DMA right up to the 8 MB limit.


In addition, the Applied Engineering GS RAM Plus is a very old card.  If
it is the original version of this card (dating back to 1986 or '87), it
might not work at all in a ROM 3 IIgs.  There may be a workaround by
using a modified PAL/GAL, and/or there may have been a later revision of
the card which is compatible with ROM 3.


Any compatibility questions here could be answered if someone else out
there has a ROM 3 IIgs with a 6 MB AE GS RAM Plus and an Apple
High-Speed SCSI card with DMA enabled, and it is working.  (I have a ROM
3 and Apple HS SCSI card, but I'm using a different memory expansion
card, which is limited to 4 MB.)

If it turns out that there is a compatibility problem, I'd suggest
getting a different memory expansion card rather than disabling DMA on
the SCSI card (though you could do that as an interim measure).

I've found that a 4 MB card has been quite sufficient (in a ROM 3), and
I have 800 KB set aside as a /RAM5 volume.  About the only time I ran
out of memory was when I was trying out one of the fax programs, which
seemed to permanently tie up rather a lot of RAM.


Another problem you may encounter is that the Zip GS may perform poorly
with large (over 4MB) memory expansion cards, though I've only seen one
report of this, and it only affected some operations.

> Given (2) 2.1 gig drives, will I be able to 'see' all that space under
> ProDos?

No.  The most you can possibly access under ProDOS-8 with an Apple
High-Speed SCSI card would be 13 partitions, each 32 MB, for a total of
416 MB.  This assumes you have no other storage devices in the slots,
and both the internal SmartPort and Disk Port (slots 5 and 6) are
disabled, i.e. no floppies.  This isn't a very useful combination.

A more probable combination (slot 5 set to SmartPort, with one or two
3.5" drives, or one 3.5" drive and /RAM5) would give you a maximum of 11
partitions, or 352 MB.

If you also enable the built-in 5.25" drive support (slot 6) you would
be down to 9 partitions, or 288 MB.


Under GS/OS, you are limited to 63 partitions over all hard drives, but
even then you wouldn't be able to access all of a single drive if you
stuck to ProDOS.  It is more usual to have a combination of ProDOS and
HFS partitions.

You are likely to have difficulty creating more than eight partitions on
a single drive.  It is possible to create more than this on a large
volume using Advanced Disk Utility (the GS/OS partitioning software) but
it is rather fiddly.

A CD-ROM drive with several multi-partition ProDOS CDs might be a better
solution.  You could copy a program or partition to a hard drive if the
program needed write access.