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The PLATO multiuser interactive computer system used – and indeed invented for this purpose – a plasma display, whose key selling point in the late sixties was that it did not need refresh, therefore did not need to be backed by video memory, at a time when memory was expensive. The resolution was 512x512. Square. Why? Well, why not? Square is the most obvious aspect ratio, and no reason not to go with that when you are building the hardware from scratch.

In the late seventies when Moore's law made video memory cheaper than a plasma screen, everyone started using CRTs. These had an aspect ratio of 4:3. (Landscape usually. The Xerox Alto rotated the picture tube ninety degrees for a portrait format. Why? Presumably because Xerox was a paper company rather than a computer company, and paper is usually used in portrait orientation.)

Except PLATO, which built a CRT terminal to replace the plasma screen, and built it around a square CRT. Why? Presumably to keep compatibility with existing software written for 512x512.

Terminology: it's difficult to search for information on this topic because 'square' in the context of CRTs was used to mean 'flat and rectangular'. Here I am using it in the more usual geometric sense of 1:1 aspect ratio.

So it seems to me that there is no technical reason why CRT monitors shouldn't be square; on the contrary, for a given area, square would seem inherently easier and cheaper than rectangular. And it would certainly be valuable for the user to be able to display extra lines of data. So why were square monitors not more widely used?

TV sets had to stay 4:3 for compatibility with existing broadcast standards. (Well you could physically make one square, but then existing broadcast content would look scrunched.)

Some early home computers used the living room TV set as display, which takes them out of scope for this question. But business computers did not, because the standard for business computing was 80 columns, which an NTSC TV set could not display readably. So they needed dedicated monitors anyway.

Conjecture: the electronics and the phosphor coating needed to be dedicated, but computer monitors used the same glass tubes as TV sets, and at each moment in time it was cheaper to buy some of the rectangular glass tubes coming from a TV factory, then to set up a dedicated production line for square tubes.

Maybe this was a bistable state? Maybe if anyone had set up a big enough production line for square tubes for computer monitors, they could've driven down the price enough to make them as cheap as the rectangular ones, and then everyone would've started using square tubes?

If that conjecture is right, then it would be all or nothing. PLATO must've set up a small production line for small numbers of square tubes (or maybe they anticipated large numbers; they were hoping to get big). But the above conjecture would weakly predict that no one else used square tubes at all.

So, the question:

Were there any square monitors other than the PLATO ones?

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    Human vision is decidedly rectangular, at least for those with two working eyes, and when people get multiple monitors, they much more frequently put them side-by-side, make them an ultrawide 8:3 or 32:9, instead of making the more square 2:3 or 8:9 ratios. It seems like the lack of square monitors comes down to people not wanting a square monitor.
    – prosfilaes
    Feb 23 at 21:26
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    I still have a set of S100 graphics boards that were designed for 512x512 display. But their output was meant for a standard 4:3 CRT, so I think it just displayed blank bars on the left and right. Feb 25 at 4:26
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    I'm pretty sure the PLATO monitor CRTs were not square. I worked in the U. Del. PLATO department part-time in the late 1970's, and we had both types of terminals. To the best of my recollection, the physical CRTs had the standard 4:3 aspect ratio. I don't recall whether the bezel opening was square -- it may have been.
    – Dave Tweed
    Feb 27 at 17:08

2 Answers 2

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The AT&T Blit 630 terminal used a 1024x1024 square CRT. As noted in the AT&T Technical Journal report,

A square CRT (cathode-ray tube) was suggested to accommodate applications written for either portrait or landscape mode.

The terminal used a Motorola 68000 as its CPU.

I haven't found a 'real' picture of a 630, all I've found are pictures of other Blit terminals, but the 630 MTG Terminal User's Guide has as Figure 1-1:

630 MTG Terminal re

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    This Page shows an AT&D advertisement brochure with what seems to be a Bilt 630 MTG with a square tube on top. Personally I have never seen such. Likewise all Bilt variants (including some 630) I could find online do only use regular 4:3 tubes.
    – Raffzahn
    Feb 24 at 0:21
  • (Tried to grab that image but the site is on our blacklist - sigh) I certainly remember using various other Blits while at Bell Labs back in the day, but don't recall seeing a 630 in the wild. Their description of 1024x1024 resolution would suggest at least some version was square.
    – Jon Custer
    Feb 24 at 14:07
  • I can insert it if you want. 1024x1024 does not imply a square screen. I guess it was just a suggestion, like mentioned in above citation.
    – Raffzahn
    Feb 24 at 14:27
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TL;DR:

There were several VDU with square resolution, even some square pixel but none I know or could find that used a square tube.

The ones with square pixel still used 3:4 tubes.


Would round ones count?

Like in early TV sets?

enter image description here

(yes, the tube under that cover is still a round one)

Or Computers?

enter image description here

Both feature round CRT, more or less covered, displaying a square picture. Quite common until manufacturing avantgarde went for rectangular tubes created for TV. There been a few 'more squarish' tubes made on the move from round to rectangular, but they vanished soon when US manufacturers caught up with German CRT technology.

Plasma in turn is a complete different development, thus it doesn't matter what production facilities were there for TV sets. Similar, the there is no existing display standard to follow. So any ratio (and resolution) could be used. going for a square one simpliefied construction by making X and Y symmetric.

A situation quite different from later LCD monitors, which had to be made to match existing display resolutions used with CRT.

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  • Even if one were using a 4:3 tube, I would think the largest square one could produce with acceptable geometry would be slightly taller than the largest 4:3 rectangle one could produce likewise, so using a 4:3 tube with a square bezel opening might be a reasonable idea.
    – supercat
    Feb 24 at 20:29

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