The video about 7-bit ASCII reminded me of my early experiences of the ASCII control codes. and frankly, there are plenty of resources online, so I'll merely recount some aspects from my memory of the early-middle "microcomputing" era.
XON/XOFF
We really did Ctrl-S and Ctrl-Q to pause and then continue program output on the screen (because it handled by emulating a terminal). These were also really used by two computers connected by a serial cable, for the receiver to signal when it was capable of receiving more content. This was for when a serial cable was a 3-wire cable - one for ground and one for transmitting bits in each direction. In this case the characters were referred to as XON and XOFF. When I could, I preferred to use a 5-wire serial cable, where the two extra wires did that stop and continue signalling instead. However, this variation of circumstance meant you often had a setting in software at each end to tell them whether or not to do XON/XOFF control.
Control-Zed
Ctrl-Z really was routinely used to indicate the end of a text file - in a way similar to what Dylan describes as being used in memory handling with C programming. This was especially so on CP/M because that system only knew how many blocks of storage a file was using, so the exact end of a text file needed the marker character (unless it coincided with the end of the last block. Even some time in the early 1990s I once had to diagnose a case of an Excel file refusing to fully load data from a text file. Sure enough it proved to have a rogue Ctrl-Z character inside, that I found with a hex dump.
Form Feed
With dot matrix and daisy wheel printers, we really did use FF to tell them to skip ahead to the next page of fan fold paper. This meant that these printers were actually counting the number of lines they'd printed so far, so as to know how many to scroll part to reach line 1 of the next page. And that also meant we had to line them with the head ready to print on line 1 before we ran a print. And, that also meant they needed to be told how many lines apart those pages were. For this reason, most (of not all) fan-fold paper supplies conformed to the American system rather than be the European A4 sizing. I could probably write a whole article just on how much complexity was available in those printers, as we are merely scratching the surface here.
Cursor Control Keys
The early screen based text editors, used the keys Ctrl-H, Ctrl-J, Ctrl-K, Ctrl-L for the "cursor" movements of left, down, up and right. Yes if you look at a QWERTY keyboard those are a run of four on a row. Two of those made some sense - Ctrl-H = Backspace for Left and Ctrl-J = Line Feed for down. I remember editing with WordMaster that way. And the makers of it, MicroPro used a different set of four for their next word editor - WordStar - that was so successful that for many years, caused the ESDX set of four control keys to become the default cursor keys that software would use. Notably the Turbo Pascal editor, and which is still echoed in the Linux editor "joe".
btw: yes, I'm aware that VI and VIM also use what I'm referring to as "the WordMaster keys" but I'm only quoting my personal heritage experience here (for otherwise, go read the Internet). I'll assume VI came first.
Keyboard Mappings
Finally, the other ASCII sequence to hardware coincidence to comment on,is that the Microbee computer (of which I owned several, and for whom I worked) used a keyboard layout based on the ADM-3A terminal. In both of these, the characters put as the SHIFT of the numeric keys, were a simple ASCII code displacement from each of the number keys - and is why there is nothing above the zero.
Ok, it's been a while since I wrote all that, but I've come back to add some notes after watching an excellent pair of videos by Dylan Beattie
The video about 7-bit ASCII reminded me of my early experiences of the ASCII control codes. and frankly, there are plenty of resources online, so I'll merely recount some aspects from my memory of the early-middle "microcomputing" era.
XON/XOFF
We really did Ctrl-S and Ctrl-Q to pause and then continue program output on the screen (because it handled by emulating a terminal). These were also really used by two computers connected by a serial cable, for the receiver to signal when it was capable of receiving more content. This was for when a serial cable was a 3-wire cable - one for ground and one for transmitting bits in each direction. In this case the characters were referred to as XON and XOFF. When I could, I preferred to use a 5-wire serial cable, where the two extra wires did that stop and continue signalling instead. However, this variation of circumstance meant you often had a setting in software at each end to tell them whether or not to do XON/XOFF control.
Control-Zed
Ctrl-Z really was routinely used to indicate the end of a text file - in a way similar to what Dylan describes as being used in memory handling with C programming. This was especially so on CP/M because that system only knew how many blocks of storage a file was using, so the exact end of a text file needed the marker character (unless it coincided with the end of the last block. Even some time in the early 1990s I once had to diagnose a case of an Excel file refusing to fully load data from a text file. Sure enough it proved to have a rogue Ctrl-Z character inside, that I found with a hex dump.
Form Feed
With dot matrix and daisy wheel printers, we really did use FF to tell them to skip ahead to the next page of fan fold paper. This meant that these printers were actually counting the number of lines they'd printed so far, so as to know how many to scroll part to reach line 1 of the next page. And that also meant we had to line them with the head ready to print on line 1 before we ran a print. And, that also meant they needed to be told how many lines apart those pages were. For this reason, most (of not all) fan-fold paper supplies conformed to the American system rather than be the European A4 sizing. I could probably write a whole article just on how much complexity was available in those printers, as we are merely scratching the surface here.
Cursor Control Keys
The early screen based text editors, used the keys Ctrl-H, Ctrl-J, Ctrl-K, Ctrl-L for the "cursor" movements of left, down, up and right. Yes if you look at a QWERTY keyboard those are a run of four on a row. Two of those made some sense - Ctrl-H = Backspace for Left and Ctrl-J = Line Feed for down. I remember editing with WordMaster that way. And the makers of it, MicroPro used a different set of four for their next word editor - WordStar - that was so successful that for many years, caused the ESDX set of four control keys to become the default cursor keys that software would use. Notably the Turbo Pascal editor, and which is still echoed in the Linux editor "joe".
Keyboard Mappings
Finally, the other ASCII sequence to hardware coincidence to comment on,is that the Microbee computer (of which I owned several, and for whom I worked) used a keyboard layout based on the ADM-3A terminal. In both of these, the characters put as the SHIFT of the numeric keys, were a simple ASCII code displacement from each of the number keys - and is why there is nothing above the zero.