IBM, sonic delay lines, and the history of the 80x24 display
============================================================
by Ken Shirriff

What explains the popularity of terminals with 80x24 and 80x25
displays? A recent blog post "80x25" motivated me to investigate
this. The source of 80-column lines is clearly punch cards, as
commonly claimed. But why 24 or 25 lines? There are many theories,
but I found a simple answer: IBM, in particular its dominance of the
terminal market. In 1971, IBM introduced a terminal with an 80x24
display (the 3270) and it soon became the best-selling terminal,
forcing competing terminals to match its 80x24 size. The display for
the IBM PC added one more line to its screen, making the 80x25 size
standard in the PC world. The impact of these systems remains decades
later: 80-character lines are still a standard, along with both 80x24
and 80x25 terminal windows.

<http://exple.tive.org/blarg/2019/10/23/80x25/>

In this blog post, I'll discuss this history in detail, including
some other systems that played key roles. The CRT terminal market
essentially started with the IBM 2260 Display Station in 1965, built
from curious technologies such as sonic delay lines. This led to the
popular IBM 3270 display and then widespread, inexpensive terminals
such as the DEC VT100. In 1981, IBM released a microcomputer called
the DataMaster. While the DataMaster is mostly forgotten, it strongly
influenced the IBM PC, including the display. This post also studies
reports on the terminal market from the 1970s and 1980s; these make
it clear that market forces, not technological forces, led to the
popularity of various display sizes.

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 true that 80-column displays were motivated by punch cards4 and
the VT100 became a standard, [2] but the rest of this theory falls
apart. The biggest problem with this theory is the VT100's display
was 80x24, not 80x25. [3] In addition, the VT100 used extra bytes of
storage for each line, so the display memory did not fit into 2K.
Finally, up until the 1980s, most displays were 80x24, not 80x25.

The DEC VT100 terminal had an 80x24 display. Over a million of them
were sold. Photo from Jason Scott, (CC BY-SA 4.0).

<http://static.righto.com/images/terminal/
865px-DEC_VT100_terminal_transparent-w300.jpg>

Other theories have been expressed on Software Engineering
StackExchange and Retrocomputing StackExchange, arguing that 80x24
terminals resulted from technical reasons such as TV scan rates,
aspect ratios, memory sizes, typography, the history of typewriters,
and so forth. There is a fundamental problem with theories that 80x24
is an inevitable consequence of technology, though: terminals in the
mid-1970s had dozens of diverse screen sizes such as 31x11, 42x24,
50x20, 52x48, 81x38, 100x50, and 133x64. [11] This makes it clear
that technological limitations didn't force terminals into a
particular size. To the contrary, as technology improved, most of
these sizes disappeared and terminals were largely 80x24 by the early
1980s. This illustrates that standardization was the key factor, not
the technology.

<https://softwareengineering.stackexchange.com/questions/148754/
why-is-24-lines-a-common-default-terminal-height>

<https://retrocomputing.stackexchange.com/questions/5629/
why-did-80%C3%9725-become-the-text-monitor-standard>

I'll briefly summarize why technical factors don't have much impact
on the terminal size. Although US televisions used 525 scan lines and
60 Hz refresh, [9] 40% of terminals used other values. [6] The display
frequency and bandwidth didn't motivate a particular display size
because terminals generated characters with a wide variety of matrix
sizes. [8] Although memory cost was significant, DRAM chip sizes
quadrupled every three years, making memory only a temporary
constraint. The screen's aspect ratio asn't a big factor because the
text's aspect ratio often didn't match the screen's ratio. [7] Of
course technology had some influence, but it didn't stop early
manufacturers from creating terminal sizes ranging from 32x8 to
133x64.

The rise of CRT terminals
=========================
At this point, a bit of history of CRT terminals will help. [11] Many
readers will be familiar with ASCII terminals, such as stand-alone
terminals like the DEC VT100, serial terminal connections via a PC,
or the serial port on boards such as the Arduino. This type of
terminal has its roots in teleprinters, electro-mechanical
keyboard/printers that date back to the early 1900s. The best-known
teleprinter is the Teletype, popular in newsrooms as well as computer
systems in the 1970s. (The Linux device /dev/tty is named after the
Teletype.) Teletypes typically printed 72-character lines on a roll
of paper. [10]

A Teletype ASR33 communicated in ASCII and printed 72 characters per
line. Hundreds of thousands of these were produced from 1963 to 1981.
The punched tape reader and punch is on the left. Photo from Arnold
Reinhold, (CC BY-SA 3.0).

<http://static.righto.com/images/terminal/
1280px-ASR-33_at_CHM.agr-w400.jpg>

In the 1970s, replacing teleprinters with CRT terminals was a large
and profitable market. AT&T introduced the Teletype Model 40 in 1973,
a CRT terminal with an 80x24 display. [12] Many other companies
introduced competing CRT terminals, and "Teletype-compatible" became
a market segment. By 1981 [11] these terminals were being used in
many roles besides replacing teleprinters and the name shifted to
"ASCII terminals". By 1985, CRT terminals were a huge success with 10
million terminals installed in the US.

The IBM 3270 terminal, specifically the newer 3278 model. From IBM
3270 Brochure (1977).

<http://static.righto.com/images/terminal/3270-operators-w400.jpg>

<http://bitsavers.org/pdf/ibm/3270/GS20-3149-0_3270_Brochure_May77.pdf>

But there's a parallel world of mainframe terminals, a world that may
be unfamiliar to many readers. In 1965, IBM introduced the IBM 2260
Display Terminal, which placed IBM's "stamp of approval" on the CRT
terminal, which had previously been "somewhat of a novelty." [6] This
terminal dominated the market until IBM replaced it with the cheaper
and more advanced IBM 3270 terminal in 1971. Unlike asynchronous
ASCII terminals that transmitted individual keystrokes, these
terminals were block oriented, efficiently exchanging large blocks of
characters with a mainframe. The 3270 terminal was fairly
"intelligent": a 3270 user could fill in labeled fields on the
screen, and then transmit all the data at once by pressing the
"Enter" key. (This is why modern keyboards often still have the
"Enter" key.) Sending a block of data was more efficient than sending
each keystroke to the computer, and allowed mainframes to support
hundreds of terminals. In the next sections, I'll discuss the 2260
and 3270 terminals in detail.

<https://en.wikipedia.org/wiki/Computer_terminal
#Block-oriented_terminal>

The chart below [6] shows how the terminal market looked in 1974. The
market was ruled by IBM's 3270 terminal, which had obsoleted IBM's
2260 terminal by this point. With 50% of the market, IBM essentially
defined the characteristics of a CRT terminal. Teleprinter
replacement was a large and influential market; the Teletype Model 40
was small but growing in importance. Although DEC would soon be a
major player, it was in the small "Independent Systems" slice at this
point.

In 1974, IBM dominated the terminal market; 50% of the terminals sold
were IBM terminals (or compatibles). From Alphanumeric and Graphic
CRT Terminals.

<http://static.righto.com/images/terminal/piechart-w400.jpg>

<http://bitsavers.org/pdf/ventureDevelCorp/
Alphanumeric_and_Graphic_CRT_Terminals_1975-1980_Nov1975.pdf>

The IBM 2260 video display terminal
===================================
The IBM 2260 was introduced in 1965 and was one of the first video
display terminals. [14] It filled three roles: remote data entry (in
place of punching cards), inquiry (e.g. looking up records in a
database), and as a system console. This compact terminal weighed 45
pounds and was sized to fit on a standard office typewriter stand.
Note the thickness of the keyboard; it reused the complex keyboard
mechanism of the IBM keypunch. [13]

IBM 2260 Display Station. Photo from IBM via Frank da Cruz.

<http://static.righto.com/images/terminal/xi05-w500.jpg>

You might wonder how IBM could produce such a compact terminal with
1965 technology. The trick was that the terminal held just the
keyboard and CRT display; all the control logic, character
generation, storage, and interfacing was in a massive 1000 pound
cabinet (below). <15> This cabinet contained the circuitry to handle
up to 24 display terminals. It generated the pixels for these
terminals and send video signals to the terminals, which could be up
to 2000 feet away.

On Mon, 29 Apr 2024 21:23:22 -0000 (UTC), Ben Collver wrote:

> The DEC VT100 terminal had an 80x24 display.

So did the VT52 before it. One of the innovations in the VT100 was it also
had a 132-column mode. In this mode, the number of displayable lines
shrank to 14, as I recall; unless you had the extra-cost “AVO” (“Advanced
Video Option”) addon, one of the features of which was enough video RAM to
keep displaying 24 lines in this mode.

It was not really a comfortable mode to use. I kept thinking something was
squeezing my eyes together ...

> Punch cards have a longer history than you might think.

Right back to about 1804, in fact. Trivia question: what were they being
used for then?

Lawrence D'Oliveiro <ldo@nz.invalid> wrote:

> On Mon, 29 Apr 2024 21:23:22 -0000 (UTC), Ben Collver wrote:
>
> > The DEC VT100 terminal had an 80x24 display.
>
> So did the VT52 before it. One of the innovations in the VT100 was it also
> had a 132-column mode. In this mode, the number of displayable lines
> shrank to 14, as I recall; unless you had the extra-cost "AVO" ("Advanced
> Video Option") addon, one of the features of which was enough video RAM to
> keep displaying 24 lines in this mode.
>
> It was not really a comfortable mode to use. I kept thinking something was
> squeezing my eyes together ...
>
> > Punch cards have a longer history than you might think.
>
> Right back to about 1804, in fact. Trivia question: what were they being
> used for then?

That would be the Jacquard loom machine.

--
^Ï^. Sn!pe, PA, FIBS - Professional Crastinator

My pet rock Gordon just is.

Ben Collver <bencollver@tilde.pink> wrote at 21:23 this Monday (GMT):
> IBM, sonic delay lines, and the history of the 80x24 display
>============================================================
> by Ken Shirriff
[snip]

Thanks for (re)posting these here! They're interesting reads.
--
user <candycane> is generated from /dev/urandom

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.

--
Dan Espen

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.

On Tue, 30 Apr 2024 03:36:51 -0000 (UTC), Ben Collver wrote:

> The said the IBM PC team felt absolutely no need to be compatible with
> other IBM products.

That in itself would seem to be an IBM tradition ...

Ben Collver <bencollver@tilde.pink> wrote or quoted:
>One Retrocomputing StackExchange answer claims that terminals with
>72-character lines show "the struggle for 80 characters", with
>72-character terminals falling short of the 80-character goal.
>However, 72-character lines were a deliberate choice to capture the
>lucrative Teletype market; teleprinters such as the Teletype Model 33
>printed 72-character lines. (The model number of the Datapoint 3300
>(1969), for instance, reflects the Teletype Model 33.)

Raymond Hettinger (transcribed, shortened and partially paraphrased
by me [Stefan Ram]):

|The line-width part of PEP 8 bugs me.
| |You have to wrap your commits in seventy-two characters. You have
|to end your lines at seventy-nine characters.
| |One time it bugs me is when I'm writing unit tests.
| |When I write unit tests, I have to start with a class, and then
|inside the class there's a "def" for tests, and then the test
|starts with a "self.assertEqual", and by then most of my line
|is gone. So by the time I get to any business logic in my test,
|I'm near the end of the line.
| |If I go over seventy-nine characters, somebody will come and
|PEP 8 me.
| |They'll come in and say: "Oh, Raymond's line hit eighty-one
|characters, I'm going to PEP 8 it!". And so, while I'm not
|looking, they come in and reformat my code.
| |They'll just throw a line break at a really awkward place.
| |Does that make the code better?
| |So, to escape that pressure, I think: Maybe I can just commit
|a little atrocity and that way no one will ever come and PEP 8 me.
|I'll just shorten my variable names.
| |Does that make the code better?
| freely adapted from Raymond Hettinger

Ben Collver <bencollver@tilde.pink> writes:

> 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.

All true.

The IBM PC was 1981. The IBM 3270 PC was 1983.

It could have been a lucky accident that the 25 line proved useful 2 years
later.

The first online system I wrote was for IBM 2260s. After I was done my
boss asked me my opinion of the IBM 3270. I read the tech manual and
decided the IBM 3270 was a piece of junk. The protocol to talk to the
thing was ridiculously complicated.

--
Dan Espen

On 30 Apr 2024 15:55:04 GMT, Stefan Ram wrote:

> |You have to wrap your commits in seventy-two characters. You have |to
> end your lines at seventy-nine characters.

I typically have my editor window widths set at about 100 characters.
And I use them all.

It is true that, in normal text, short lines are easier to read than
long ones (hence why newspapers have so many columns). But in
programming, a lot of my lines is taken up with indentation. So the
nonblank parts are not necessarily that long. E.g.

scallop = Path \
(
[
Path.Segment
(
points =
(
Path.Point((0, 0), False),
Path.Point
(
pt = Vector(1, 1) * (1 - params["fraction"]) / 2 * step,
off = False
),
Path.Point
(
pt =
Vector(1, 1) * step * params["sharpness"] / 2
+
Vector(1, 1) * 2 * params["depth"] * step_normal,
off = True,
),
Path.Point
(
pt =
Vector(1, 1) * step * (1 - params["sharpness"] / 2)
+
Vector(1, 1) * 2 * params["depth"] * step_normal,
off = True,
),
Path.Point
(
pt = Vector(1, 1) * (1 - (1 - params["fraction"]) / 2) * step,
off = False
),
Path.Point
(
pt = Vector(1, 1) * step,
off = False
)
),
closed = False
)
]
).transform(Matrix.scale(scallop_size))

On Tue, 30 Apr 2024 15:32:48 -0400, Dan Espen wrote:

> I read the tech manual and
> decided the IBM 3270 was a piece of junk. The protocol to talk to the
> thing was ridiculously complicated.

True of a lot of IBM technology, is my impression. Note that their idea of
a networking architecture, SNA, did not actually support peer-to-peer
connections until about the mid-1980s.

Their labs produced a lot of research papers and patents, but it seemed to
me very little of the clever stuff actually made it into their products.

On 2024-04-30, Lawrence D'Oliveiro <ldo@nz.invalid> wrote:
> On Tue, 30 Apr 2024 15:32:48 -0400, Dan Espen wrote:
>
>> I read the tech manual and
>> decided the IBM 3270 was a piece of junk. The protocol to talk to the
>> thing was ridiculously complicated.
>
> True of a lot of IBM technology, is my impression. Note that their idea of
> a networking architecture, SNA, did not actually support peer-to-peer
> connections until about the mid-1980s.

Ahhh... Memories.

SNA should not 'appen

On 2024-04-30, Stefan Ram <ram@zedat.fu-berlin.de> wrote:
> Raymond Hettinger (transcribed, shortened and partially paraphrased
> by me [Stefan Ram]):
>
>|The line-width part of PEP 8 bugs me.
>|
>|You have to wrap your commits in seventy-two characters. You have
>|to end your lines at seventy-nine characters.
>| ...
>|So, to escape that pressure, I think: Maybe I can just commit
>|a little atrocity and that way no one will ever come and PEP 8 me.
>|I'll just shorten my variable names.
>|
>|Does that make the code better?

Thanks, that was a fun read.

That makes the code better suited for a more chill community.

On 2024-04-30, Dan Espen <dan1espen@gmail.com> wrote:
> All true.
>
> The IBM PC was 1981. The IBM 3270 PC was 1983.
>
> It could have been a lucky accident that the 25 line proved useful 2 years
> later.
>
> The first online system I wrote was for IBM 2260s. After I was done my
> boss asked me my opinion of the IBM 3270. I read the tech manual and
> decided the IBM 3270 was a piece of junk. The protocol to talk to the
> thing was ridiculously complicated.

Interesting! Those were before my time. The original article states
that the Enter key was left over from times when it was too expensive to
stream individual characters between all terminals. So the terminals
were smart enough to collect an entire record of data and send it all in
one batch when the user pressed the Enter key. This made me wonder
about the details. What format did they use to draw a form on the
terminal and define the fields in a record? I bookmarked that for a
later deep dive down the rabbit hole at bitsavers.

Dan Espen <dan1espen@gmail.com> wrote:
> Ben Collver <bencollver@tilde.pink> writes:
>>
>> Also, 3270 emulation was not a requirement or goal for the IBM PC,
>> and didn't lead to the 25th line.
>
> All true.
>
> The IBM PC was 1981. The IBM 3270 PC was 1983.
>
> It could have been a lucky accident that the 25 line proved
> useful 2 years later.

Knowing IBM, I would say selecting a monitor with 25 lines
was because it was the cheapest option at the time :)

<snip>

--
[t]csh(1) - "An elegant shell, for a more... civilized age."
- Paraphrasing Star Wars

On Tue, 30 Apr 2024 21:32:12 -0000 (UTC), Ben Collver wrote:

> The original article states that the Enter key was left over from times
> when it was too expensive to stream individual characters between all
> terminals.

Funny, users of minicomputers were doing exactly that with ASR-33
teletypes since the early 1960s, if not before.

The Enter key would have come from electric typewriters, where it was
needed because they didn’t have manual carriage-return levers any more.

Lawrence D'Oliveiro <ldo@nz.invalid> writes:

> On Tue, 30 Apr 2024 15:32:48 -0400, Dan Espen wrote:
>
>> I read the tech manual and
>> decided the IBM 3270 was a piece of junk. The protocol to talk to the
>> thing was ridiculously complicated.
>
> True of a lot of IBM technology, is my impression. Note that their idea of
> a networking architecture, SNA, did not actually support peer-to-peer
> connections until about the mid-1980s.

It sure looked like IBM refused to release simple solutions because they
were afraid the competition could produce something compatible.

> Their labs produced a lot of research papers and patents, but it seemed to
> me very little of the clever stuff actually made it into their products.

The S32/S34 line had a nice design until they decided to make it
complicated with the S/38 AS/400 stuff.

--
Dan Espen

On Tue, 30 Apr 2024 20:52:29 -0400, Dan Espen wrote:

> It sure looked like IBM refused to release simple solutions because they
> were afraid the competition could produce something compatible.

I think Hanlon’s Razor applies: “never attribute to malevolence that which
can be explained by stupidity”.

In other words, the complexity comes from Conway’s Law: “any piece of
software reflects the organizational structure that produced it”. Or in
more general form, “any engineering endeavour reflects the organizational
structure that produced it” (including both software and hardware). So the
complexity and inflexibility in IBM’s products comes directly from the
labyrinth that was its internal corporate culture.

> The S32/S34 line had a nice design until they decided to make it
> complicated with the S/38 AS/400 stuff.

System/38 was the first (only?) commercial product that implemented
capabilities and also built a database into the OS.

Dan Espen <dan1espen@gmail.com> wrote:
>
>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.

Yes. 3270 emulation was one of the applications delivered with the machine
when it was first introduced, with a coax interface card being available.
It was expected to be one of the major uses of the machine.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."