reenigne

> with the smaller CPUs you can lookup exactly how long each instruction will take and thus get the timing right

Reminds me of the good old demo scene hack to get 18-bit color[1] back in the VGA days (and probably earlier) by changing the color palette per pixel through careful timing of the instructions.

IIRC you ignore the pixel values entirely, writing effectively a single "color", ie palette index, and then just change that single palette entry per pixel, timed so it's ready just when the output DAC is clocked to the next pixel.

edit: I forgot which demos I've seen this effect in, but searching for it led me down a marvelous rabbit hole where I stumbled over someone[2] managed[3] to get 1k colors over CGA[4], apparently discussed here[5] a couple of years ago.

[1]: https://en.wikipedia.org/wiki/Video_Graphics_Array#Color_palette

[2]: https://int10h.org/blog/2015/04/cga-in-1024-colors-new-mode-illustrated/

[3]: https://www.reenigne.org/blog/1k-colours-on-cga-how-its-done/

[4]: https://en.wikipedia.org/wiki/Color_Graphics_Adapter

[5]: https://news.ycombinator.com/item?id=21992870

This wouldn't be complete without mentioning the enhanced CGA version a lot of Europeans experienced via Amstrad/Schneider PCs in the 80s (they tended to be the cheapest way to get a PC here, back then).

"The Amstrad used an "enhanced" CGA graphic mode, which could display 640x200 pixels with 16 colors (or grayscale)."

http://www.old-computers.com/museum/computer.asp?c=183&st=1

http://www.nostalgianerd.com/amstrad-pc1512

There were probably at least five pieces of software released which supported this mode. :)

The PC1512 came bundled with the GEM windowing system from Digital Research, including a paint program: http://www.reenigne.org/computer/gempaint.gif as well as a fairly state of the art graphical BASIC: http://www.reenigne.org/computer/basic2.gif, https://www.youtube.com/watch?v=dDL8w_Mi49A (video in EGA though).

CISC and RISC are mostly an ISA concept.

Most chips are "microcoded", at least here and there. The term does not define a whole micro-architecture, esp in modern complex ones, but I'm not really sure how you would implement old school CISC chips without microcode concepts. The 8086 was microcoded: https://www.reenigne.org/blog/8086-microcode-disassembled/. It basically means that "you" program some low level internal details of a chip, e.g. the muxes connecting various buses to execution units. Most of the time the "you" is only the chip designers, and it is stored mostly in a ROM. Sometimes microcoding is accessible by actual software programmers, but it is quite rare.

And modern u-ops are not necessarily like what was done at the time of old-school microcode.