PC displays almost always targeted 4:3 CRT displays. And indeed, VGA and most super-VGA modes had 4:3 aspect ratio resulting in square pixels - except the odd 5:4 1280*1024 mode. This mode even caused 17"/19" LCD monitors to actually be 5:4, before widescreen 16:9 took over.

How did this odd resolution become sort-of standard? Edit: Why didn't they go with a corresponding 4:3 resolution instead, like 1280*960 or 1360*1020 (to fit in 4MB for 24-bit)?

To clarify, here are the resolutions as I remember them:

|                   | Resolution           | aspect ratio |
| (pre-VGA madness) | various              | various      |
| VGA               | 640*480              | 4:3          |
| Super VGA         | 800*600              | 4:3          |
| Super VGA         | 1024*768             | 4:3          |
| Super VGA         | 1152*864             | 4:3          |
| Super VGA         | 1280*1024 <<<<<      | 5:4 <<<<<    |
| Super VGA         | 1600*1200            | 4:3          |
| Widescreen        | 1920*1080 and others | 16:9         |
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    For reference regarding SuperVGA modes, see Ralf Brown’s table of resolutions supported by INT 0x10 on various cards, and the lists of modes supported in VBE. – Stephen Kitt Jul 3 '19 at 10:11
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    actually, the weirdest thing is that we perceive 5:4 as weird :-D why they were all sticking to 4:3 when there are so many other options (unlike in TV, where all screens have to be 4:3 if the source material is 4:3) – szulat Jul 4 '19 at 12:42
  • If one of the answers below solves your question, be sure to accept it by clicking the checkbox. – DrSheldon Jul 5 '19 at 0:51
  • @DrSheldon: Unfortunately none do. While they provide good discussion of what happened, I didn't get a good answer as to why. – Jonathan Jul 7 '19 at 7:06
  • Super-VGA is 800x600. 1024x768 is XGA. 1280x1024 is actually Super-XGA. – mirabilos Aug 21 '19 at 18:43

VGA's 640x480 mode was the first to offer square pixels and an exception among all VGA modes available (320x200, 640x200, 640x350 and 720x400 for Text). Square pixels weren't the standard back then.

Adding video modes in later (Super) VGA was kind of a marketing game to offer higher numbers to outpace competition. First it was Colour, like offering 640x480 in 256 colours,later it became as much about higher resolutions. At the time, there where many other resolutions seen as 'standard' beyond 800x600, like 1024x600, 1152x768 or 1280x800 - the later was quite prominent, as it fits (almost) exactly 1 MiB of RAM in 8 bit mode.

1280x1024 is again based on nice power of two values (like 1024x768), thus easy to handle and maximizing the use of RAM, as it exactly filled 1.25 MiB in 8 Bit Mode and 2.5 MiB in 16 Bit Mode (*1) Both sizes could be well added as a series of 5 RAM chips to the card. In addition it's worth considering that later single chip VGA designs were usually fully programmable, thus able to offer next to any resolution (within their pixel clock that is).

Some years later 1280x1024 got a revival when upcomming (relative) low cost LCD manufacturing process passed the 1024x748 ability for 15". After all, such LCDs don't react as flexible as CRTs to various pixel per line rates.

*1 - Mostly forgotten today, but 16 bit colour was a huge thing - for a few years :)

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    Do you know why 1280×1024 was preferred to 1280×960 (apart from occupying more of the available memory), or why the “standard” 1152×864 workstation resolution never took off on PCs? I’m also curious about 1280×800 — I’m not aware of a SuperVGA board which supports that (before they became fully programmable); where was it prominent? – Stephen Kitt Jul 3 '19 at 9:46
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    No hard facts, I would go with the usual 'more is better' aproach. Especially as a light distortion of ~6% horizontal is next to invisible to most users. 1152x864 is a great reminder. Not sure either. 1280x800: Back in the mid 90s it could be ordered with stock SIEMENS clones (PCD-3*) for example. – Raffzahn Jul 3 '19 at 9:56
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    I remember 1280x800 as being prominent in laptops and possiblly LCD monitors from the mid to late 2000s. – Peter Green Jul 3 '19 at 17:10
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    "Both sizes could be well added as a series of 5 RAM chips to the card." Did such video cards actually exist? I only remember video cards with even multiples of 1 MiB of memory. – snips-n-snails Jul 3 '19 at 18:55
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    @StephenKitt why? Because it provides more (almost a vertical inch at 72 dpi) "screen" space. – RonJohn Jul 4 '19 at 0:35

Quoting Wikipedia, it seems to be at least two factors:

The availability of inexpensive LCD monitors has made the 5:4 aspect ratio resolution of 1280 × 1024 more popular for desktop usage during the first decade of the 21st century.

(from here)

The 1280 × 1024 resolution became popular because at 24 bit/px color depth it fit well into 4 megabytes of video RAM. At the time, memory was extremely expensive. Using 1280 × 1024 at 24-bit color depth allowed using 3.75 MB of video RAM, fitting nicely with VRAM chip sizes which were available at the time (4 MB): (1280 × 1024) px × 24 bit/px ÷ 8 bit/byte ÷ 2^20 byte/MB = 3.75 MB

(from here)

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    I believe 1280*1024 predated commonplace LCDs - my 1994 Cirrus Logic GD5428 supported it (ref) – Jonathan Jul 3 '19 at 8:55
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    Also, they could do some 4:3 resolution to fix 4MB (about 1365*1024, obviously rounded for 8-multiples)/1024, like they did 1152*864 for almost exactly 1 megapixels. – Jonathan Jul 3 '19 at 8:59
  • Well, I'm just trying to answer the question by providing some arguments that seem reasonable. It's true that the 1280x1024 was around long ago, but it's also true that cheap monitors that supported that were common in late 90's and early 2000's. Bought some of them myself. OTOH, the OP asks "why the resolution was sort of standard" not "why didn't they keep making standards with 4:3 aspect ratio". – DroidW Jul 3 '19 at 9:05
  • Well the OP (=me) did mean "why not 4:3" :) I edited the question to clarify. – Jonathan Jul 3 '19 at 10:31
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    @Jonathan The 1280x1024 5:4 aspect ratio display, with a square pixels, only became a thing with 1280x1024 5:4 aspect ratio LCD panels. On 4:3 aspect ratio CRTs, 1280x1024 has non-square pixels. This was actually a problem for games, since 1280x1024 could be displayed on either a 5:4 or 4:3 display and there was no way to infer which was the case. They either had to assume an aspect ratio (and so have a distorted display on the other), have two 1280x1024 choices, or allow selecting the aspect ratio separately. – Ross Ridge Jul 3 '19 at 16:47

1280x1024@24-bit fits in 4 MiB. Why wouldn't you take extra screen space?

Keep in mind that games didn't usually run in 1280x1024 at the time. Back before LCDs became the dominating screen technology, you didn't care about the "native resolution" of the display - you didn't get the ugly "one pixel is stretched over two physical pixels, its neighbour only has one physical pixel". Even modern LCDs tend to look awful at their non-native resolutions (not helped by the use of sub-pixel rendering of fonts etc.), but the same thing wasn't true with CRTs.

So you had your workstation running 1280x1024, giving you the most of your 4 MiB graphics card. And when you wanted to play a game, it switched the resolution to something like 800x600 or 1024x768. The image was just as clear in both cases, you didn't get any weird aliasing or sizing artifacts.

This changed when LCDs came around; native resolution is a big deal on LCDs. Running a 800x600 game on an 1280x1024 LCD (of the time, though many quality issues remain to this day) will result in many artifacts. But here's the thing - LCDs weren't for games. No gamer would ever voluntarily use an LCD - they were designed for office use (and of course, portable computers - but that's a whole another can of worms). They had poor colours, poor response times, bad aliasing issues and couldn't adapt to other resolutions well. It made perfect sense to give the most screen space possible, which with the (then rather standard) 4 MiB graphics cards was 1280x1024@24-bit (while also giving nice fallback to 16-bit and 8-bit for smaller VRAM).

It took many years for LCDs to become mainstream even among gamers (mostly because of their convenience - size, weight, cost etc.). By then, 1280x1024 was already the standard, and most importantly, games became largely aspect ratio agnostic anyway. The next big jump had to wait for people watching movies on their computers, which helped the move to 16:9 and 16:10 (for that handy extra bit of vertical space).

Of course, there are other possible options that have pretty much the same benefits (or take other trade-offs). In the end, it's just that one of those dominated the others. Following the leader is often a good idea, since it makes it easier to reach a bigger portion of the market.

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