4 ms·

My professor likes to tell this story about keyboard buffers that I never quite understood. Basically, in this old time terminal setup he would start typing the

by mcny 9y ago

My professor likes to tell this story about keyboard buffers that I never quite understood. Basically, in this old time terminal setup he would start typing the password before the prompt showed up or something and when it did, it would just sail through. Sort of like how I can apt upgrade while apt update is still running but fancier and a couple of decades before...

jdmichal 9y ago
You can still do this in at least some shells. PowerShell buffers input if the running program doesn't capture it. If I have a build and execute commands in the history, I can hit up-up-enter twice in a row to start the build and queue the execution command.
- dep_b 9y ago
  I remember people doing that on an AS/400 ramming keystrokes for 5 seconds and then waiting 15 seconds for the system to arrive in the right screen, sometimes even already filling the fields from muscle memory. The first five lines of address data were already entered before the screen loaded.
  - coleca 9y ago
    When I was in high school I had a job after school where they still had a PDP/11 w/real DEC VT-100 terminals. The kid next to me used to do data entry and would get far ahead of the input screen. Except when he made a mistake, and he often did, it would beep. But because he was so far ahead when he made a mistake it would beep for 2 minutes straight. Every time. Max-volume. Soo.. When he left his desk, I went in and hit SHIFT-SETUP, turned the audible BEL off in the VT-100 setup menu and enjoyed the silence. When I came back in the office the next day, there was a technician from Digital with the terminal in what looked like 100 pieces on the desk trying to "fix" it. He was pretty upset when he realized it wasn't the speaker and the setting was just turned off (why he didn't check that first, I'll never know). Needless to say as a teenager, I kept quiet about the whole thing.. until now..
    - exikyut 9y ago
      Oh wow. That is awesome.
vanderZwan 9y ago
That "old time" hurts a bit.. I haven't tried this recently, but I distinctly remember doing this in the early versions of Ubuntu.
colejohnson66 9y ago
The computers at my old job working as a cashier did that. It made working with produce so much faster because as soon as I heard the beep, I could move on to the next item, even if the screen hasn’t updated yet.
whatever_dude 9y ago
That's what happens when you read from a keyboard buffer. Since the buffer is not being read (and not cleared) until a prompt is in the screen, you can type whether you want and it'll get dumped and processed whenever needed. Not that long ago really, that's how it worked in DOS and most other terminals.
- kijin 9y ago
  It still works. I can ssh into a machine and start typing commands before the shell prompt appears. The commands will appear in the terminal once the connection is established and the shell is ready.
- chasd00 9y ago
  Isn't the keyboard buffer a part of the physical keyboard circuitry and interface? Hitting enter triggers an IRQ to flush the buffer, so if the CPU is too busy to handle the IRQ then things queue up until the CPU can get around to handling it. If that's the case, for this "feature" not to work would require a very low level architectural change to keyboards. (it's been many years since i've thought about this though)
  - singingboyo 9y ago
    Keyboard buffers are decidedly not on the physical keyboard. The keyboard might have a very small one, but the IRQ is triggered on every input. The buffer in question is, for a tty, a driver-level buffer that holds on to the data until something reads it. If a command doesn't read it (which things like apt-get update don't) then it'll get read as the next command. Of course, most terminals these days are ptys accessed via emulators, so the buffer is actually part of the emulator, but the same idea applies.
    - chasd00 9y ago
      ah, the more you know :) I would have been shocked if i remembered all that correctly
jasonkostempski 9y ago
I see that buffer effect all the time still.
darylfritz 9y ago
> Sort of like how I can apt upgrade while apt update is still running but fancier You can link two commands together with the "AND IF" operator sudo apt update && sudo apt upgrade Furthermore, you also have `||` which is the logical or, and also `;` which is just a separator which doesn't care what happend to the command before.

by mcny 9y ago

jdmichal 9y ago

You can still do this in at least some shells. PowerShell buffers input if the running program doesn't capture it. If I have a build and execute commands in the history, I can hit up-up-enter twice in a row to start the build and queue the execution command.

dep_b 9y ago
I remember people doing that on an AS/400 ramming keystrokes for 5 seconds and then waiting 15 seconds for the system to arrive in the right screen, sometimes even already filling the fields from muscle memory. The first five lines of address data were already entered before the screen loaded.
- coleca 9y ago
  When I was in high school I had a job after school where they still had a PDP/11 w/real DEC VT-100 terminals. The kid next to me used to do data entry and would get far ahead of the input screen. Except when he made a mistake, and he often did, it would beep. But because he was so far ahead when he made a mistake it would beep for 2 minutes straight. Every time. Max-volume. Soo.. When he left his desk, I went in and hit SHIFT-SETUP, turned the audible BEL off in the VT-100 setup menu and enjoyed the silence. When I came back in the office the next day, there was a technician from Digital with the terminal in what looked like 100 pieces on the desk trying to "fix" it. He was pretty upset when he realized it wasn't the speaker and the setting was just turned off (why he didn't check that first, I'll never know). Needless to say as a teenager, I kept quiet about the whole thing.. until now..
  - exikyut 9y ago
    Oh wow. That is awesome.

vanderZwan 9y ago

That "old time" hurts a bit.. I haven't tried this recently, but I distinctly remember doing this in the early versions of Ubuntu.

colejohnson66 9y ago

The computers at my old job working as a cashier did that. It made working with produce so much faster because as soon as I heard the beep, I could move on to the next item, even if the screen hasn’t updated yet.

whatever_dude 9y ago

That's what happens when you read from a keyboard buffer. Since the buffer is not being read (and not cleared) until a prompt is in the screen, you can type whether you want and it'll get dumped and processed whenever needed. Not that long ago really, that's how it worked in DOS and most other terminals.

kijin 9y ago
It still works. I can ssh into a machine and start typing commands before the shell prompt appears. The commands will appear in the terminal once the connection is established and the shell is ready.
chasd00 9y ago
Isn't the keyboard buffer a part of the physical keyboard circuitry and interface? Hitting enter triggers an IRQ to flush the buffer, so if the CPU is too busy to handle the IRQ then things queue up until the CPU can get around to handling it. If that's the case, for this "feature" not to work would require a very low level architectural change to keyboards. (it's been many years since i've thought about this though)
- singingboyo 9y ago
  Keyboard buffers are decidedly not on the physical keyboard. The keyboard might have a very small one, but the IRQ is triggered on every input. The buffer in question is, for a tty, a driver-level buffer that holds on to the data until something reads it. If a command doesn't read it (which things like apt-get update don't) then it'll get read as the next command. Of course, most terminals these days are ptys accessed via emulators, so the buffer is actually part of the emulator, but the same idea applies.
  - chasd00 9y ago
    ah, the more you know :) I would have been shocked if i remembered all that correctly

jasonkostempski 9y ago

I see that buffer effect all the time still.

darylfritz 9y ago

> Sort of like how I can apt upgrade while apt update is still running but fancier You can link two commands together with the "AND IF" operator sudo apt update && sudo apt upgrade Furthermore, you also have `||` which is the logical or, and also `;` which is just a separator which doesn't care what happend to the command before.