18

80x24 characters seems to be a very common default for terminal windows. This answer provides a very good historical reason as to why the width is 80 characters.

But why is the height commonly 24 (or 25) lines?

Community
  • 1
hotpaw2
  • 7,938
  • 4
  • 21
  • 47
  • 3
    Save your history questions for next week :P. Too late now though: http://meta.programmers.stackexchange.com/questions/3546/programmers-se-contest-the-complete-outline – Dynamic May 15 '12 at 20:28
  • 3
    80×25 is actually more common – vartec May 15 '12 at 20:34
  • @vartec : Edited the question for either 24 or 25 lines. – hotpaw2 May 15 '12 at 20:37
  • I don't know about 25 lines, but whenever I open PuTTY it defaults to 80x24. – TND May 15 '12 at 20:39
  • 4
    Probably partly because 80x25 is just under 2K. Makes it easy to have a 2K screen buffer. – Gort the Robot May 15 '12 at 22:21
  • @StevenBurnap Isn't 80X25 exactly 2000? – Kris Harper May 15 '12 at 23:41
  • Yes. And 80x26 is 2080, which is bigger than 2K. Having a 2K+32byte buffer would be awkward, more awkward than having 24 bytes in the buffer that aren't used. – Gort the Robot May 16 '12 at 02:29
  • @KrisHarper: I think the VT100 was 24 lines plus a status line, though some other display devices are 24 lines without any status indicator. From a hardware perspective, counting display addresses linearly is a little harder than adding eight bytes of padding every three rows, but the latter approach leaves 64 bytes scattered throughout memory. – supercat May 24 '16 at 22:18
  • The width is 80 because the original punch cards (1 line of code) were 80. – Chris Catignani Jun 07 '19 at 14:40

2 Answers2

24

Early terminals were built around the same cathode ray tubes that were used for televisions. In the 1960's and 1970's these were all 4:3 aspect ratio.

If the display needs to fit 80 characters across the width then given the aspect ratio of the standard characters which was taller than 3:4 (if I remember correctly) and allowing for a larger space between lines than between characters you get to fit 24 or 25 lines on the display.

I haven't done the exact maths because I can't remember (or find) the exact character aspect ratio or line spacing.

Community
  • 1
ChrisF
  • 38,878
  • 11
  • 125
  • 168
  • 1
    That depends on the bitmap used for the characters. I cannot find an image of the physical screen to see. Also note that 132 character widths were available. –  May 15 '12 at 22:20
  • 1
    @ThorbjørnRavnAndersen - I'm having problems finding exact numbers too. If I remember correctly the aspect ratio of the characters used for the 132 character displays were different - thinner than the standard 80 character displays. – ChrisF May 15 '12 at 22:23
  • @ThorbjørnRavnAndersen If it helps, I've got an 80x25 ASCII terminal from IBM, of which the 25th line is a status line. I had brightness turned down when I took it but if it helps, here's a photo. http://i.imgur.com/bU2Hd1X.jpg – Wyatt Ward Jan 04 '16 at 19:52
9

The height of the vt100 terminal.

Emulators get the best vt100 compatability at that size.