Thanks for the info, gumby. As you point out, the amount of bus bandwidth consumed by the display is a big thing. It seems a bit crazy that the processor was running microcode to copy all the pixels to the display in 16-word chunks, 30 times a second. (In a "normal" system, the video hardware fetches characters or pixels from memory. But in the Alto, the processor was running instructions to feed the pixels to the display over and over as they were being sent to the screen.)
I'm confused about your portrait vs landscape comments, though. The ADM-3A, Hazeltine 2000, VT-52, 3270, as well as Datapoint, Four Phase, Viatron, etc had a horizontal display, not a portrait display.
> It seems a bit crazy that the processor was running microcode to copy all the pixels to the display
It seems crazy today but not in context. There wasn't video hardware in today's sense. There were either mainframes (with channel controllers) with the terminal doing the "rendering" or minicomputers and microcomputers in which the CPU did everything (which is what I guess it was like before the mainframe era).
You can see this reflected in Unix, and therefore in Linux: unix was developed for the PDP-7 (and later -11), a reimplementation of some of the ideas of Multics, which ran on a mainframe. So C's IO was "user mode" (I seem to remember a funny line in the original version, something like, "You mean you I have to call a function to do IO?") and the kernel had expensive, primitive IO capabilities and involved the CPU in everything. Well, there wasn't any alternative in the smaller PDP line (FWIW PDP-10 were larger machines than the -7 or -11, though only the later models had channel IO).
Memory mapped IO was not uncommon on minicomputers.
> I'm confused about your portrait vs landscape comments, though. The ADM-3A, Hazeltine 2000, VT-52, 3270, as well as Datapoint, Four Phase, Viatron, etc had a horizontal display, not a portrait display.
I'm confused / unclear. Those terminals had more columns than rows, true, but the character positions were rectangular. So the ADM-3 and the Datapoint were rather square, actually, because TV tubes were squarish, not paper-like as I claimed. I think I biased my memory because I used a bunch of hacked terminals like AAA Ambassadors which could cram 80x48 rather than 80x24 and because of the rectangular characters were portrait-ish. Unfortunately it's too late to go back and edit my comment.
Ah yes, Ambassadors! Portrait mode "dumb" terminals, but highly valued for coding given their 48 lines of text. (Twice the normal in the VT-100 days.)
Had a lot of those first at the Columbia computer center back in the DEC-20 days, later at the Fairchild AI Lab startup (DEC-20's and LISPMs), and even later at Imagen (a Stanford TeX project spinoff building the first commercial laser printers before Apple and Xerox released theirs).
I'm confused about your portrait vs landscape comments, though. The ADM-3A, Hazeltine 2000, VT-52, 3270, as well as Datapoint, Four Phase, Viatron, etc had a horizontal display, not a portrait display.