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I can't get the page to open but the title of the HN submission is nonsense. Terminal is 80x25 because that's how big terminals were back in the day (for very
by yodon 7y ago
I can't get the page to open but the title of the HN submission is nonsense.
Terminal is 80x25 because that's how big terminals were back in the day (for very long ago values of back in the day and for purely bandwidth driven reasons).
Pre-Mac (technically pre-Lisa) Black and White CRT displays which were made using then-current CRT TV technology which had just enough analog bandwidth to show 80 columns of 5 pixel by 7 pixel characters, with one pixel separation (480 pixels horizontally [edit added: those are US numbers, European TV's had slightly higher bandwidth but that's a different topic]) and most could only show 24 such characters vertically due to the 4x3 aspect ratio used in essentially all CRTs of the day. 24x80 was the industry standard for a screen of text for purely CRT bandwidth reasons. So why 25 lines? Because a few super cool terminals allowed you one extra line for showing status below a conventional 24x80 layout, hence 25x80 (vertical squeeze didn't pose bandwidth or pixel separation problems on black and white displays of that era). Terminal naturally went with the cool kid size of 25x80. No civil war bank notes involved, just the bandwidth of then-current generation TV display technology and a fortuitous coincidence that punch cards had 80 columns.
[edit added] Apple][ and other similar era devices had even lower character counts because they hooked up to color TV's which had roughly similar bandwidth but needed to spread that bandwidth across three phosphors per pixel so far fewer pixels available on screen.
- tyingq 7y agoApple has nothing to do with 80x25. That all happened before they existed. So I'm confused about all the references to them.
- yodon 7y agoCorrect, 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.
- fouc 7y ago80x25 comes from VT100's 2 kilobytes display memory limit. >Then in 1983 the Apple IIe was introduced, the first Apple computer to natively support an 80×24 text display, doubling 40×24 of previous Macs.
- yodon 7y ago> 2 kilobytes display memory limit That too
- kaslai 7y agoAlso, (almost) all humans have two feet because shoes come in pairs of two. /s
- IIAOPSW 7y agoYour being downvoted but you have a valid point. People should look up the NTSC/PAL standard for how analog TV screens worked. There were only ~560 scan lines in the raster pattern (vertical and horizontal blanking intervals notwithstanding). With a character height of 7 pixels/scan lines + one for spacing that gets you 70 lines of text on screen. Even if the punch card machines gave you more memory, actually using it would have required buying a special purpose TV. Eventually we did get CRT monitors which were specific for computers instead of television, but that wouldn't be economically viable at the time.
- tyingq 7y agoThe downvoting is likely because 80x24/25 happened well before home PCs that displayed via NTSC/PAL. And many of those early terminals also supported a 132 column mode.
- IIAOPSW 7y agoWhat were the earlier non-home computers displaying on?
- tyingq 7y agoCRT, but not via RF modulators, NTSC, PAL, etc.
- IIAOPSW 7y agoThat's very odd. Why did they invent a new CRT format and spend the cost of the hardware to implement it instead of using an off the shelf TV?
- tyingq 7y agoBecause TVs didn't have high quality video inputs. Old Apples, C64s, etc, came with a "tiny tv broadcaster" (RF modulator) that broadcast the signal on channel 3. In shit NTSC or PAL quality, which is lower resolution than what the CRT can display.
- Taniwha 7y agoYup that's my memory 80x24 until the VT100 came along. The phrase "Then in 1983 the Apple IIe was introduced, the first Apple computer to natively support an 80×24 text display, doubling 40×24 of previous Macs" is rather cringeworthy and shows a misunderstanding of the time (first of all Macs were introduced in '84 .... Mac and AppleIIs were competing architectures from Apple)
- peteri 7y agoIt's stupid mistakes like this that make me doubt the rest of the article. Besides many Apple ][ had an 80 column card already.