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ASCII was designed for typewriters, not video terminals. "×" is the same as "x". "÷" can be made by overstriking ":" and "-". The quotation marks needed to als

by pdw 7y ago

ASCII was designed for typewriters, not video terminals. "×" is the same as "x". "÷" can be made by overstriking ":" and "-". The quotation marks needed to also function as accents, by overstriking: "ë é è". CR and LF are separate operations on a typewriter. You might want to simulate bold type by sending CR and retyping part (or all) of a line. [ and ] were added for the benefit of Algol, and other programming languages with an Algol-derived syntax. Though it was recognized that these characters were less essential, and these code points were left undefined in ISO 646, the international version of ASCII. This is also why the brackets were put in the alphabet part of the ASCII table, in other countries these code points would've been used for letters that weren't part of the English alphabet. It was anticipated that some manufacturers would use a 6-bit subset of ASCII. (Even 5-bit and 4-bit subsets were considered.) This would mean that the lower case block would be collapsed on the upper case block. So they needed to find characters that could be useful but would still make sense when rendered as [ and ]. Hence { and }. Hope this helps. A lot of thought went into ASCII, but many of the considerations became obsolete during the 70s. And you could say that any terminal that does not support overstriking, does not properly support ASCII :)

gumby 7y ago
> It was anticipated that some manufacturers would use a 6-bit subset of ASCII. Not only anticipated but quite common on 36-bit machines where you could put six characters in a word. In those days “byte” meant a contiguous string of bits so a byte pointer could point to one, two, ... 63 bits in some architectures so SIXBIT characters were not at all inconvenient > You might want to simulate bold type by sending CR and retyping part (or all) of a line. Some video displays (“glass teletypes” — these took character data and were not pixel addressable) supported this feature. Printers pretty much all did — tolerances were not great so overprints were always darker. Backspace (^H) was used for this too. This is one reason why backspace and delete have been different characters to me. Note that the 0xFF value for delete goes back to paper tape: it punched out all the holes in a column so could overwrite any other character. Yes, you deleted by doing backspace delete.

by pdw 7y ago

gumby 7y ago

> It was anticipated that some manufacturers would use a 6-bit subset of ASCII. Not only anticipated but quite common on 36-bit machines where you could put six characters in a word. In those days “byte” meant a contiguous string of bits so a byte pointer could point to one, two, ... 63 bits in some architectures so SIXBIT characters were not at all inconvenient > You might want to simulate bold type by sending CR and retyping part (or all) of a line. Some video displays (“glass teletypes” — these took character data and were not pixel addressable) supported this feature. Printers pretty much all did — tolerances were not great so overprints were always darker. Backspace (^H) was used for this too. This is one reason why backspace and delete have been different characters to me. Note that the 0xFF value for delete goes back to paper tape: it punched out all the holes in a column so could overwrite any other character. Yes, you deleted by doing backspace delete.