[AUUG-Talk]: Re: [BUGA] Sell me an Apple!

Peter Jeremy peterjeremy at optushome.com.au
Tue Mar 28 17:56:27 EST 2006

On Mon, 2006-Mar-27 22:08:54 +0930, David Newall wrote:
>us "why 1984 [wasn't] like 1984."  They gave us Macintosh.  It was a new
>platform in many ways, including what appeared at the time to be a
>ludicrously large address range, and Apple, in keeping with the habits
>they had adopted from day one, split that space according to various
>purposes; so much address space for ROM, so much for hardware I/O; so much
>for a frame buffer; and so on.

Sounds perfectly reasonable.  In fact far more reasonable on the Mac
than the Apple-II.  The M68K (and 6502) didn't/doesn't have a separate
I/O address space so you have to carve out space for I/O devices.  The
PC also carved up the address space with a generous allocation to
ROM and memory-mapped hardware because no-one would ever need more
than 640KB.

In the case of the Mac, there was absolutely no scope for hardware
expansion - all you could do was change the RAM size.  Given this,
it's quite reasonable to carve up the 24-bit physical address space
to minimise the address decoding hardware.

IMHO, the biggest novelty in MacOS was the use of double-indirect
pointers everywhere to allow memory to be compacted by just moving
blocks around in RAM.

Peter Jeremy

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