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Where Did 1280x1024 Come From?

Posted by Cliff on from the behind-the-technology dept.

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?"

2 of 42 comments (clear)

  1. 1280x960 by XoXus · · Score: 3

    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.

  2. DRAM rows is why by dvd_tude · · Score: 3

    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