> shadow RAM at the same address as the ROMs,

> I found something vaguely the opposite with Apple II.

Being at the same address as ROM, the 2 x 8k of RAM was
probably largely unused by most people, and certainly the O/S
didn't use it unless asked to. To access an 8k bank you had to
turn the corresponding BASIC or KERNEL ROM off and hand
over control to ML. Being out of reach of the O/S (BASIC
variable storage etc) it was a very useful place to store large
amounts of data like bitmapped screens / character sets, or ML
routines

The memory used for BASIC normally went from $0801 to
$9FFF. Programs built from $0801 upwards and variables
were stored from $9FFF downwards. Inevitably there would
be corruption and crashes as either the program got longer and
ran into the variables it created or you went a bit mad with
variable or string creation.

The BASIC ROM (and the underlying RAM) went from $A000
to $BFFF, but of course you couldn't turn BASIC off to access
the $A000 RAM for BASIC variables. However, by making an
editable soft copy of BASIC, it was (ISTR) possible to change
the default vectors and store variables at $CFFF -> $C000, which
was RAM not overlaid by ROM, the KERNEL ROM being at
$E000 to $FFFF, and other parts of the O/S at $D000 - $DFFF

Joe
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