Extremely CISC instructions

Josh Dersch derschjo at gmail.com
Wed Aug 25 12:08:04 CDT 2021

On Mon, Aug 23, 2021 at 5:38 PM Tom Stepleton via cctalk <
cctalk at classiccmp.org> wrote:

> Hello,
> For the sake of illustration to folks who are not necessarily used to
> thinking about what computers do at the machine code level, I'm interested
> in collecting examples of single instructions for any CPU architecture that
> are unusually prolific in one way or another. This request is highly
> underconstrained, so I have to rely on peoples' good taste to determine
> what counts as "interesting" here.

I'll submit the Xerox Alto, with its extensions to the base DG Nova
instruction set.  It included "CONVERT", used to render font glyphs to the
screen, and of course the legendary "BITBLT" for transferring bitmaps
across arbitrary bit boundaries.  Both of these were complicated
operationst, and the latter revolutionized computer graphics...

See p. 18 and 22 of http://bitsavers.org/pdf/xerox/alto/AltoHWRef.part1.pdf.

(The Three Rivers PERQ included a similar "RASTEROP" instruction in its
repertoire, which was similar to BITBLT but also allowed for various
logical operations to be applied to the source and destination.)

- Josh

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