4 ms·

The distant legacy of terminal emulators

11 points by tsujp 5y ago

theamk 5y ago
There is no need to go to source code to view gemini:// URLs, they work just fine via any existing browser using portals. So here is a formatted link of the text above: https://portal.mozz.us/gemini/drewdevault.com/2021/10/05/Terminal-emulation-legacy.gmi https://portal.mozz.us/gemini/drewdevault.com/2021/10/05/Ter...
gumby 5y ago
Unix adopted the pty from earlier systems btw (dmr would have seen them while he was at MIT working on Multics). Most of the logic in the teletype was mechanical, not electronic, which explains some of the assignment of the ascii characters. Carriage return: on a typewriter (and thus on teletypes and their competitors), the carriage carried the paper (held on a rubber roller with springs and a rod). On a typewriter and somme teletypes, the carriage started on the right (for English) hanging off the side of the machine. As you pressed a key the character would be pressed against the paper at the center of the device. Then a ratchet would automatically advance the whole carriage leftwards so the next character would appear to the right of the previous one. When you were done with a line you would push a lever to advance the roller (feed the paper by one line) and, under muscle power, drag the carriage back to the right side. This technology was in common use into the late 1990s. Quite early on, someone got the idea that they could put all these characters on a cylinder (print head) and move just that. More parts, but greater reliability as you were moving something small. Easier to print on a roll of paper too! Because this arrangement was so complicated it wasn’t adopted by mechanical, niter most electrical typewriters, though the electric “selectric” by IBM was a notable exception. The “shift” key comes from the typewriter: lower and upper case characters were embossed above each other on their stalk and the shift key would literally move the entire print apparatus (which had a metal bar for each letter) upwards. It sometimes required a LOT of force. Unlike “shift”, the term “case” (as in upper and lower case) comes from printing when type was held in big wooden cases and far predates the technology above by centuries.

11 points by tsujp 5y ago

There is no need to go to source code to view gemini:// URLs, they work just fine via any existing browser using portals. So here is a formatted link of the text above: https://portal.mozz.us/gemini/drewdevault.com/2021/10/05/Terminal-emulation-legacy.gmi https://portal.mozz.us/gemini/drewdevault.com/2021/10/05/Ter...

gumby 5y ago

Unix adopted the pty from earlier systems btw (dmr would have seen them while he was at MIT working on Multics). Most of the logic in the teletype was mechanical, not electronic, which explains some of the assignment of the ascii characters. Carriage return: on a typewriter (and thus on teletypes and their competitors), the carriage carried the paper (held on a rubber roller with springs and a rod). On a typewriter and somme teletypes, the carriage started on the right (for English) hanging off the side of the machine. As you pressed a key the character would be pressed against the paper at the center of the device. Then a ratchet would automatically advance the whole carriage leftwards so the next character would appear to the right of the previous one. When you were done with a line you would push a lever to advance the roller (feed the paper by one line) and, under muscle power, drag the carriage back to the right side. This technology was in common use into the late 1990s. Quite early on, someone got the idea that they could put all these characters on a cylinder (print head) and move just that. More parts, but greater reliability as you were moving something small. Easier to print on a roll of paper too! Because this arrangement was so complicated it wasn’t adopted by mechanical, niter most electrical typewriters, though the electric “selectric” by IBM was a notable exception. The “shift” key comes from the typewriter: lower and upper case characters were embossed above each other on their stalk and the shift key would literally move the entire print apparatus (which had a metal bar for each letter) upwards. It sometimes required a LOT of force. Unlike “shift”, the term “case” (as in upper and lower case) comes from printing when type was held in big wooden cases and far predates the technology above by centuries.