3 ms·
Correct, this is explaining that prior to the Mac terminals used then-current TV tech which had these limitations, and that the limitations were even more sever
by yodon 7y ago
Correct, this is explaining that prior to the Mac terminals used then-current TV tech which had these limitations, and that the limitations were even more severe on display of color text, as was the case for the Apple ][ (intended to show that it's not even true that terminals were 24x80 or 25x80, it's that black and white terminals were that size because they could be and color terminals had even fewer characters because thats all they could have).
As they say, correlation does not imply causation. It's a coincidence that Black and White tv screens from long ago had just enough pixels to display 80 columns of text.
- tyingq 7y agoThere's enough "pixels" for 132 columns, and many old terminals (vt220 for sure) could do that. The RF modulator needed by Apple/C64/etc did perhaps limit it to 80...it wasn't the tube.
- yodon 7y agoTerminals like the VT220 were much more expensive because they needed much higher bandwidth analog electronics than conventional TV circuitry (the limit isn't on the B/W tube, it's on the electronics that steer the beam around)
- tyingq 7y agoI think there's not much difference in the horizontal/vertical driver circuits. Here's the (pretty pedestrian and likely not different from a b/w tv) diagram of the horizontal driver for a vt220: https://imgur.com/a/xvq1ukV https://imgur.com/a/xvq1ukV The shown MC1391P is, in fact, called a "horizontal TV processor" by Motorola. I'm sure there's other stuff that made them expensive (CPU, memory, video logic, etc). Edit: Lol at imgur for marking my screenshot as "erotic" and NSFW.
- yodon 7y agoAwesome find. That said I think the bandwidth issue was less with the semiconductor electronics in that diagram and more with the big analog electronics that actually controlled the gun directly (the box labeled horizontal driver in your image)
- tyingq 7y agoHere's the other two boxes: https://imgur.com/a/yJH9QYu https://imgur.com/a/yJH9QYu (Which Imgur also finds erotic and NSFW. Odd)
- kps 7y agoNo. Terminals did not use TV screens. Monochrome CRTs do not have pixels.
- yodon 7y agoA monochrome CRT tube and a black and white TV tube are the same physical device just packaged and sold to different customers. The bandwidth of the electronics driving the electron beam sets a maximum modulation frequency and hence a minimum line pair spacing. That minimum line pair spacing sets the effective pixel separation as directly as the shadow mask pitch does on a color CRT. The bandwidth was set by the TV standards, which were in turn set by what was feasible to manufacture economically in those days.
- kps 7y agoNo, terminals rarely if ever used TV-type tubes (before the home computer era had people using actual TVs) — usually not even the same phosphors — nor the same signal rates, because TV rates would make no sense for a terminal. ‘Manufacture economically’ was not the same thing for a business product as a home appliance — an IBM 3278 in today's dollars cost $13000. This isn't lost-clay-tablet stuff. There are manuals and schematics online.
- tyingq 7y agoThe vt220 manual I found suggests the same CRT scan rates. 15.75 Khz horizontal, for example, with the reference freq coming from a very TV specific Motorola IC. Perhaps different phosphors, sure.
- jacobush 7y agoDifferent phosphors for sure. My terminals (I've had 3 or 4 DEC and others) hade a very visible afterglow. Very stable and flickerfree compared to my CRT TVs.
- kps 7y agoThe VT220 was a very late terminal, though and I was trying to focus on early models where the line length decision was not just inherited from the previous CRT model (i.e. the VT220 had 80 columns because the VT100 did because the VT50 did).