
Why I loved the Apple II (memory-mapped video) - davewiner
http://scripting.com/stories/2012/04/26/whyILovedTheAppleIi.html
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ggchappell
> That idea didn't make it to the Macintosh, though I wish it had. But they
> had something even cooler, Quickdraw. Those were the days.

If by "that idea", you mean a memory-mapped display, then it certainly did
make it to the original Macintosh -- as well as a number of subsequent models.
The original Mac display was a little 9-inch CRT, 512 x 342 black-and-white-
only pixels. One bit per pixel, so each scan line was 64 bytes. 342 lines made
for a bit over 21K of display memory, out of 128K total. And that had to hold
the OS & applications, too. (Those were the days....)

OTOH, I believe these Macs had only a single memory-mapped display buffer, not
the multiple buffers that the Apple II line had. And of course no Mac ever had
a text display buffer. And, true, you weren't _supposed_ to write to the
display buffer yourself. If you were a Good Person, then you used QuickDraw
and the Window Manager. But you _could_ write to it; no memory protection back
then.

Another funky bit of info you didn't mention: the Apple II display buffers
were not exactly 2-D arrays. The screen lines were not stored in order. I seem
to remember that Woz mixed them up because it allowed for easier computation
of the memory location of a character (?). (If this sounds implausible,
remember that, back then, multiplication was _hard_.) And there were "holes"
in the buffer that were not used for display. 1024 bytes for the text display
buffer only had to hold 40 x 24 = 960 characters, leaving 64 bytes of free
space scattered throughout the buffer. These extra locations were allowed to
be used as scratch space by I/O devices: 8 bytes for each slot.

