Re: 8MB GS RAM cards

[spec@vax2.concordia.ca (Mitchell Spector)]

In article rubywand@swbell.net writes...

>Mitchell Spector writes ...
>
>     A problem is only going to arise *IF* your using devices which use
>DMA (Direct Memory Access - a process in which the device can interact
>directly with memory, bypassing the processor) and you have 5 megabytes
>or more (4 MB is the DMA limit) present in the expansion slot. Such
>devices can include SCSI or IDE controllers, video capture boards, etc.
>The RamFAST SCSI does tricks to get around it, combined with certain
>designed memory boards, but it doesn't always work and risky IMHO. (some
>have report success, others have reported failure).
>
>     Thanks for the information; however, it leaves us with a lot of
>questions. For one thing, what happens if you try to boot a System 5.0.4
>diskette on a ROM-03 with one of the two current 8MB boards?

    I'm not sure what you mean exactly. The version of System Software
used makes _no_ difference as far as the Apple IIgs seeing what memory
is available for software to use (they all see the same thing as far
as what is plugged into the GS's Memory Expansion Slot).

    Using a RAM Disk on a ROM 3 (there is no "ROM 03" btw) with 7 MB
in the expansion slot is a different issue. In that situtation, you
need System 6.0.1 to get around a firmware bug that disables (or
ignores?) the RAM Disk setting. When you boot System 6.0.1, the GS
will "beep" an extra time as it reboots the GS (probably just before
or slightly after the GS/OS "Welcome" screen) to create the RAM Disk.

>And, of course, the Accelerator + DMA business is a mine field of non
>information.

    Well the TransWarp GS was flakey as far as being DMA compatible
or friendly as far as I know, so you often have to disable the DMA
setting on your hardrive controller. As for the Zip GS, the early
cards (revision 1.00 and 1.01 specifically) had problems with DMA
as well, but the revision 1.02 board fixed that.

    When I began upgrading my GS, I made sure to get DMA compatible
stuff to work within even 4 MB. That is why I have a RamFAST SCSI,
RAM GS board and a Zip GS (rather than some mess like an AE memory
card, AE TransWarp GS and Apple Rev C SCSI board). Just having 4 MB
in the expansion slot doesn't neccessarily mean DMA compatibility
if your add-on cards are *not* DMA friendly (i.e. AE hardware).

>     Users should not need to blow an extra $40-$50 to experiment with
>8MB and, then, discover their setups won't work. Once again, why don't
>the 8MB Expansion RAM card makers just say what works with what and how
>well?

    Well I never saw any need for more than 4 MB in the expansion
slot, my ROM 3 runs quite well with a 5 MB memory total (1.125 MB
on the main board, plus 4 MB in the expansion slot). Having 8 MB
is more for Gee-Whiz value than any partical use with existing,
and quite conceivably, future software as well. It is alot like
having your GS running at 16 MHz for the fun of it, although that
isn't going to corrupt files at random (although it may crash and
lock-up instead at random). ;-)

Mitchell Spector
spec@vax2.concordia.ca