On Tue, 29 Mar 2016 14:20:35 +0300 Mihai Popescu <mih...@gmail.com> wrote:
> I want to get and idea of what was or is an old true hardware UNIX > terminal. I was a DEC PDP/11 TSX over RT-11 guy back then, but as I remember, a terminal was a television that printed letters and numbers plus a keyboard on which you could type. The television and keyboard connected to the computer with a serial cable (RS-232). The serial cable conducted 1 byte letters, numbers, and a few control and special characters, in each direction. So even a pig slow serial connection could fill up the television pretty fast: The computer had no concept of pixels. To convert letters and digits from the computer to screen pixels, the television part of the terminal contained a hardware-implemented character generator. Similarly, switch pairs, from the keyboard, representing key presses, were converted, at the terminal, to ascii bytes before being sent to the computer. The benefits were many. This was an incredibly thin interface, such that pretty much anything that could send and receive ascii bytes could be used interchangeably. The 1 byte per letter meant the serial connection wouldn't be taxed too heavily. The offloading of letter to graphics to the terminal meant the computer, which had less power than today's cell phones, could spend its time running jobs rather than shuffling pixels. And one benefit that carries over to today: The thin ascii interface meant the terminal would come up live incredibly early in the boot, which helped a lot in troubleshooting and bootstrapping up to a useful system. I can't count the times when, faced with a no-boot, partial POST computer, I wish I had a terminal to plug into the serial port, probably after removing the video card. Sure, I could use another computer plus minicom, but minicom itself introduces so many variables it's not worth it. SteveT Steve Litt March 2016 featured book: Quit Joblessness: Start Your Own Business http://www.troubleshooters.com/startbiz
