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Where Did 1280x1024 Come From?
Alan Shutko asks: "I was playing with different resolutions recently, and got confused.
640x480, 800x600, 1024x768, 1152x864, 1400x1050, 1600x1200, they all have a 4x3 aspect ratio. But 1280x1024 has a 5x4 aspect ratio.
What's up with this? Somewhere in the annals of computing history, someone must have come up with 1280x1024. Why did they choose such an odd aspect ratio?"
Okay, so it isn't a nice multiple of good numbers, but here's the resolution I've come up with: 1320x992. The number of pixels on the screen is within approximately 0.1% of 1280x1024, so it should theoretically work with any monitor that supports 1280x1024.
I have pasted a few modelines below. The most important number for a lot of people is the dotclock (120 in the example). You can bring that down or up, depending upon how high of refresh rates you can use with your system. IIRC, this runs at about 60 Hz, but it may be a bit higher (65 or so). Please also realize that xvidtune may be of use.
Also note that I'm not a genius when it comes to this stuff, and it could cause bad things to happen (though most modern displays can shut off when fed a bad signal..)
Modeline "1320x992" 120 1320 1348 1516 1752 992 994 999 1036
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Ski-U-Mah!
640x480 is the resolution of a North American TV screen, which is in a 4:3 ratio. In fact, you'll find that all the standard settings are in the same 4:3 ratio.
...phil
...phil
"For a list of the ways which technology has failed to improve our quality of life, press 3."
Interesting, but is that really the case? I just measured mine, and it has a 4x3 aspect ratio.
320*200=64000
I think that this mode was popular because the complete video memory fit into one memory segment. No need for page flipping a-la ModeX.
I still remember the days of bypassing PSET and using my own Pixel Routines in QBASIC.
DEF SEG = &HA000 'the VGA segment
'fill screen with red:
FOR i = 0 TO 64000
POKE i, 4
NEXT
Those were the days. Direct memory access under DOS. Without fear of the BSOD, without fear of infringing on another process' memory... [drool]
WWJD -- What Would Jimi Do?
I am quite civilized, and I should be brought a beer immediately. -- Bruce Sterling
Matrox G200/G400 will do that mode nicely. Your monitor may not like it, however. I had to tweak my Sony 21/XF86Config for an hour to get it to sync up correctly. I had some luck with it on an ATI Rage Pro, but the card has so many non-redeeming qualities I'd shy away from it, even if it is cheap.
OT, but I ran some benches of my new V3 3000 (replacing a burned out ATI) against my old SLI V2s.. The V2's kicked its ass, by up to 40%. I sincerely hope the 'Bigger, Badder' V3 models really are.. (Scariest part? I have 64M of video subsystem memory in there now)
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The comments about memory adderssing make sense for the horizontal size, but not necessarily for the vertical. That said, it is definitely easier to get a 4040-like counter to reset every 1024 ticks than every 960 ticks - but this is trivial.
I think the reason may be that older systems actually used 24-bit color, often with no underlay/overlay/alpha channel. This gives 3 bytes per pixel, for a total of 3.75 Meg for the display. This fits comfortably within a 4M framebuffer. The next higher multiple of 128 for the horizontal is 1408, with a 1056 vertical (for 4:3), and that is too much for a 4M framebuffer.
I know that back in 1987 (and probably before), the SGI Iris (with a whopping 25MHz R3000 and 32M RAM!) had a 1280x1024x24bpp display. (of course, that was 24 bits color, 24 bits z-buffer, 2 bits overlay, 2 bits underlay, and another 24bit+24bit rendering buffer, for a total of 100 bits/pixel!)
This may be another one of those "They're doing it, so we might as well, too" kind of things.
- The Sigless Wonder
The simple answer is that while TV's have a 4:3 aspect ratio, PC monitors have a 5:4 aspect ratio. That's why DVD's always seem just a little stretched. Some decoder cards actually letterbox the display to retain the approximate ratio of actual TV screens, which inevitably results in scaling artifacts unless you're cranking it out at 1080i resolution.
Anyways.. 1280x1024, in addition to offering memory-aligned scanlines as stated in every other comment, provides perfectly square pixels, which comes in pretty handy for graphics work.
-Billco, Fnarg.com
Various Macintosh computers have supported various of the popular resolutions, but the one I always run into is Apple's 1152x870. When I render a 3D graphic full size desktop picture, I must go out of my way to support 1152x870. I have to trim off 6 scan lines when moving it to a PC.
Another is 800x600 (4:3) and Apple's 832x624. Apple supports 800x600 on some Macs, 832x624 on others, and both on other models.
I'll see your senator, and I'll raise you two judges.
Ideally, you'd have 1280x960, but since 960 isn't a multiple of 128 (or 256), it messes up various hardware blitting methods.
One of the popular VGA modes was 320x256 (which is in the 5:4 ratio). It meant that you could have an array of scanlines, and index them with a single byte (with no wastage).
David.
For mostly obscure hardware reasons, early DRAM/VRAM graphics controller implementations favored horizontal resolutions that were a multiple of the row size. 1280 is divisible by 256, the row size of a 64K DRAM.
One of those obscure reasons was address translation. If you form the linear framebuffer address as (2048*y)+x, it made doing blt hardware much easier: just map x and y onto the appropriate row and column bits.
Another of those reasons was being able to load the video shift registers at the same times each line. This made the timing control easier to do in the logic of the day (think MSI counters and gates.)
Modern gfx conrollers refresh the display using periodic burst DRAM access instead of actual shift registers; and they have hardware to help deal with the x-y to linear address translation. So the whole issue of row size pretty much goes away.
dvd_tude
"I'm ANN LANDERS!! I can SHOPLIFT!! " - Zippy