Re: IIgs RAM card Question

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

Supertimer <supertimer@aol.com> wrote:

> "John King" <joki@eskimo.com> wrote:
> 
> >What is the difference between this card and an Apple card for the //e?
> 
> Mainly the fact that the IIe treats the memory as an 8-bit
> computer would and the IIGS treats its memory as a
> 16-bit computer with a 24-bit address would.  The IIe can
> only see 64k of memory at once, so larger memory cards
> divide the memory into banks and the IIe switches
> between these to access memory beyond the first 64k
> bank.

It depends which card you are talking about.  This description is
correct for auxiliary slot RAM cards (extended 80-column card, and third
party cards like the RamWorks).  Apple's auxiliary slot card only has
one bank (64KB), while the RamWorks supports multiple banks.

For Apple's "Apple II Memory Expansion Card", which operates in a
standard slot, the extra memory is accessed through a one byte window in
the I/O space, with a three byte address register which increments
automatically when the data register is read or written.  They are
called "slinky" cards because of the way in which the access location
"slinks" through the memory on the card.

The standard slot cards work in any Apple II with slots, whereas the IIe
auxiliary slot (bank switch) cards only work in the IIe.

There are equivalents to both types of card for the IIc: Apple makes one
that works like their standard slot "slinky" card (but it requires the
latest motherboard revision).  Applied Engineering makes a multi-bank
card that works like their RamWorks card for the IIe.  It works in all
IIc models.

The auxiliary slot and standard slot cards have advantages and
disadvantages:

- Memory management is trickier with an auxiliary slot card, since you
  have to do bank switching.

- Some parts of the auxiliary slot card are harder to use, due to the
  language card arrangement of the Apple II, and the way in which
  auxiliary memory bank switching is implemented.  It is easier if
  the application avoids using about 16KB out of each 64KB bank.

- You need a patched copy of ProDOS or a driver loaded at runtime to
  support a RAM disk in an auxiliary slot card.  The standard slot
  cards have a firmware driver, which is detected automatically by
  ProDOS.

- You can't boot from a RAM disk in an auxiliary slot memory card, but
  you can from a standard slot card (since it has firmware).

- Standard slot cards may be slower to access, because data has
  to be copied out of the card before it can be used.  In some cases,
  data in an auxiliary slot card may be accessed directly, depending
  on bank switching issues.  In particular, code in auxiliary bank
  codes can usually be executed directly, while code in a standard
  slot card's RAM must be copied into main memory before it can be
  executed.

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