Comment by kstrauser

Comment by kstrauser 12 hours ago

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True, but I don’t think there was a common reason to ever send a linefeed without going back to the beginning. Were people printing lots of vertical pipe characters at column 70 or something?

It would’ve been far less messy to make printers process linefeed like \n acts today, and omit the redundant CR. Then you could still use CR for those overstrike purposes but have a 1-byte universal newline character, which we almost finally have today now that Windows mostly stopped resisting the inevitable.

saila 10 hours ago

> now that Windows mostly stopped resisting the inevitable

I've been trying to get Visual Studio to stop mucking with line endings and encodings for years. I've searched and set all the relevant settings I could find, including using a .editorconfig file, but it refuses to be consistent. Someone please tell me I'm wrong and there's a way to force LF and UTF-8 no-BOM for all files all the time. I can't believe how much time I waste on this, mainly so diffs are clean.

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floren 11 hours ago

As I understand it (this may be apocryphal but I've seen it in multiple places) the print head on simple-minded output devices didn't move fast enough to get all the way back over to the left before it started to output the next character. Making LF a separate character to be issued after CR meant that the line feed would happen while the carriage was returning, and then it's ready to print the next character. This lets you process incoming characters at a consistent rate; otherwise you'd need some way to buffer the characters that arrived while the CR was happening.

Now, if you want to use CR by itself for fancy overstriking etc. you'd need to put something else into the character stream, like a space followed by a backspace, just to kill time.

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  • kstrauser 10 hours ago

    I don't think that's right. Not saying that to argue, more to discuss this because it's fun to think about.

    In any event, wouldn't you have to either buffer or use flow-control to pause receiving while a CR was being processed? You wouldn't want to start printing the next line's characters in reverse while the carriage was going back to the beginning.

    My suspicion is there was a committee that was more bent on purity than practicality that day, and they were opposed to the idea of having CR for "go to column 0" and newline for "go to column 0 and also advance the paper", even though it seems extremely unlikely you'd ever want "advance the paper without going to column 0" (which you could still emulate it with newline + tab or newline + 43 spaces for those exceptional cases).

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    • floren 9 hours ago

      I've seen this explanation multiple times through the years, but as I said it's entirely possible it was just a post-hoc thing somebody came up with. But as you said, it's fun to argue/think about, so here's some more. I'm talking about the ASR-33 because they're the archetypal printing terminal in my mind.

      If you look at the schematics for an ASR-33, there's just 2 transistors in the whole thing (https://drive.google.com/file/d/1acB3nhXU1Bb7YhQZcCb5jBA8cer...). Even the serial decoding is done electromechanically (per https://www.pdp8online.com/asr33/asr33.shtml), and the only "flow control" was that if you sent XON, the teletype would start the paper tape reader -- there was no way, as far as I can tell, for the teletype to ask the sender to pause while it processes a CR.

      These things ran at 110 baud. If you can't do flow control, your only option if CR takes more than 1/10th of a second is to buffer... but if you can't do flow control, and the computer continues to send you stuff at 110 baud, you can't get that buffer emptied until the computer stops sending, so each subsequent CR will fill your buffer just a little bit more until you're screwed. You need the character following CR (which presumably takes about 2/10ths of a second) to be a non-printing character... so splitting out LF as its own thing gives you that and allows for the occasional case where doing a linefeed without a carriage return is desirable.

      Curious Marc (https://www.curiousmarc.com/mechanical/teletype-asr-33) built a current loop adapter for his ASR-33, and you'll note that one of the features is "Pin #32: Send extra NUL character after CR (helps to not loose first char of new line)" -- so I'd guess that on his old and probably worn-out machine, even sending LR after CR doesn't buy enough time and the next character sometimes gets "lost" unless you send a filler NUL.

      Now, I haven't really used serial communications in anger for over a decade, and I've never used a printing terminal, so somebody with actual experience is welcome to come in and tell me I'm wrong.

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      • kstrauser 8 hours ago

        That's fascinating! They got a lot of mileage out of those 2 transistors, didn't they?

        But see, that's why I think there has to be more to it. That extra LF character wouldn't be enough to satisfy the timing requirements, so you'd also need to send NUL to appropriately pad the delay time. And come to think of it, the delay time would be proportional to the column the carriage was on when you sent the CR, wouldn't it? I guess it's possible that it always went to the end but that seems unlikely, not least because if that were true then you'd never need to send CR at all, just send NUL or space until you calculated it was at EOL.

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