Re: IBM, sonic delay lines, and the history of the 80x24 display

On 2024-04-30, Dan Espen <dan1espen@gmail.com> wrote:

Ben Collver <bencollver@tilde.pink> writes:
>

Some theories about the 80x24 and 80x25 sizes
=============================================
Arguments about terminal sizes go back decades, [5] but the article
80x25 presented a detailed and interesting theory. To summarize, it
argued that the 80x25 display was used because it was compatible with
IBM's 80-column punch cards, [1] fits nicely on a TV screen with a
4:3 aspect ratio, and just fit into 2K of RAM. This led to the 80x25
size on terminals such as the DEC VT100 terminal (1978). The VT100's
massive popularity led to it becoming a standard, leading to the
ubiquity of 80x25 terminals. At least that's the theory.

>
>
It's always be obvious to me that the PC was 80x25 so that it could
accurately emulate a 3270 24 line display.
>
A 3270 HAS a 25th line where is displays some additional information
like whether the keyboard is locked.  There were 24 lines of data and a
25th line for status information.

There's something about that in the comments section of the original
article:

The 3277 didn't have a status line, but three status lights next to the
display. It had 24 lines in total. The status line (Operator Information
Area) was introduced in the 3278. This can be verified in the manuals,
which are online at bitsavers.

<http://bitsavers.org/pdf/ibm/3270/>

Also, 3270 emulation was not a requirement or goal for the IBM PC, and
didn't lead to the 25th line. I would much prefer to have a tidy story
where the 3270 led to the PC's display, but unfortunately that's not the
case. I talked to two of the original IBM PC engineers to check on this.
The said the IBM PC team felt absolutely no need to be compatible with
other IBM products. In particular, several features of the PC made 3270
compatibility harder: the use of ASCII instead of EBCDIC, little-endian
words, and 10 function keys instead of 12.