alt Hacker NewsThis is by design, so that case conversion and folding is just a bit operation.
The idea that SOH/1 is "Ctrl-A" or ESC/27 is "Ctrl-[" is not part of ASCII; that idea comes from they way terminals provided access to the control characters, by a Ctrl key that just masked out a few bits.
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Yes, the diagram just shows the ASCII table for the old teletype 6-bit code (and 5-bit code before), with the two most significant bits spread over 4 columns to show the extension that happened while going 5→6→7 bits. It makes obvious what was very simple bit operations on very limited hardware 70–100 years ago.
(I assume everybody knows that on mechanical typewriters and teletypes the "shift" key physically shifted the caret position upwards, so that a different glyph would be printed when hit by a typebar.)
I guess it's an age thing, but I thought this was really basic CS knowledge. But I can see why this may be much less relevant nowadays.