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Thread: Changing refresh rate in MS-Dos - Possible?...

  1. #1

    Default Changing refresh rate in MS-Dos - Possible?...

    Hey guys,

    I think I already know the answer to this question (and it's "no"), but still figure I ask to see if there's some way:

    Is it possible to change the monitor refresh rate in MS-Dos? Reason I am asking is because I get terrible eye strain (and a headache) within 5 minutes whenever I use a CRT monitor that's not at least set to 85hz to reduce the flickering.

    On my old DOS machine, I can't stand any full screen applications, because the (to me) noticeable flicker of the CRT is nausea inducing and painful to my eyes. This has been an issue all my life by the way, for some reason I seem to be more sensitive to flickering screens than most people. This was somewhat of an issue when I was a kid, as all we had were CRT's and it was just all horrible to look at for me. Way back when, when I discovered the "85hz" refresh rate setting in Windows 98, it was absolute heaven for my eyes. No more flickering.

    Anyway, I am using a modern TFT monitor on my old DOS machine and this completely fixes the problem, but would like to use the CRT, just for old-times sake.

    Anyone know of a way to have DOS use a 85hz refresh rate? If that's impossible, that's fine. I'll just keep using the TFT.

  2. #2
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    There is no generic utility, no. It was possible to change the refresh rate with some cards using the utilities that came with those cards. I seem to recall my ATI 3D Expression+PC2TV card could store user preferences as to what refresh rate each video resolution came up in. This sometimes wreaked havoc with games, so YMMV.

    If you use 1980s-era DOS systems, you can use monochrome cards and monitors, which have very strong phosphor persistence -- there is no flickering at any refresh rate.
    Offering a bounty for:
    - Documentation and original distribution disks for: Panasonic Sr. Partner, Corona PPC-400, Zenith Z-160 series
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  3. #3

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    It depends on which video card you have installed (or video chipset, if it's built into the motherboard). In the '90s, many of them provided DOS utilities to let you change the default refresh rate for each graphics mode. Text mode, as well as CGA and EGA compatibility modes, however, are usually always stuck at the VGA default of 70 Hz.

    60 Hz was the default for VGA's 640x480 graphics mode, which can cause visible flicker on a CRT, however that was not such a big deal in the DOS era because 1.) most DOS applications used darker colors, such as a blue or black background, rather than the bright white background typical of Windows and other GUIs; and 2.) most DOS applications didn't use 640x480 graphics mode all the time anyway. And also to some degree, 3.) people were simply more used to CRTs back then, and didn't complain about the flicker or the 15.7 kHz flyback oscillator whine, because they had grown up with it and learned to ignore it.

    Also if you were rich enough and lived in a PAL region, you could buy a fancy CRT TV which scanned at 100 Hz instead of 50 Hz.

  4. #4
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    It depends on the video card and video modes. Some cards did come with DOS tools for setting the refresh rates, but usually only for higher SVGA resolutions. For VESA 3.0 compatible cards and video modes, there was Unirfrsh.

    What video card/chipset are you using?

  5. #5

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    The system I am running is your average mid '90's one. It's a p5 100mhz with a standard S3 Virge video card, so nothing fancy. I guess I am just stuck with using the modern TFT monitor, and that's fine.

    Maybe I should install Windows 95 on this (it's now running DOs 6.22), and see if that allows me to use the CRT...

  6. #6

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    TheGreatCodeholio developed a tool for danooct1 that allowed DOS to run at 59.94Hz. You can find it here:
    https://github.com/joncampbell123/do...w/vga/vga240.c

    and executables to run here:
    https://github.com/joncampbell123/doslib/releases
    Join your local penny pincher movement today!

  7. #7

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    Well, I did actually go ahead and installed Windows 95 OSR 2.5. This allows me to at least run the monitor at 75hz most of the time, which is a whole lot better. When I set Windows 95 to 85hz, it'll tell me it's running at 85, but it will in fact run at 76hz. Not sure what's up with that, I might have to find a better display driver or something.

    Either way, I think I'm good now.

    Thanks guys!

    Also, my videocard is not an S3 Virge as I thought, but in fact an S3 Trio64+. Not that it matters a whole lot, but still...

  8. #8
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    Quote Originally Posted by Kazblox View Post
    TheGreatCodeholio developed a tool for danooct1 that allowed DOS to run at 59.94Hz. You can find it here:
    https://github.com/joncampbell123/do...w/vga/vga240.c

    and executables to run here:
    https://github.com/joncampbell123/doslib/releases
    BTW, there are caveats to this: Because it works by hooking int13, only well-behaved software will show up in 59.94. Also, it achieves this by forcing the 480-line mode, so the aspect ratio will, unavoidably, be incorrect. Finally, any games that require the original 70 Hz refresh rate for proper timing are going to run slowly. Other than those limitations, most stuff (generic games like Sierra games) should work just fine.

    IIRC, the utility is more meant for capturing DOS graphical software in a framerate more friendly to video editing
    Offering a bounty for:
    - Documentation and original distribution disks for: Panasonic Sr. Partner, Corona PPC-400, Zenith Z-160 series
    - Music Construction Set, IBM Music Feature edition (has red sticker on front stating IBM Music Feature)
    - Any very old/ugly IBM joystick (such as the Franklin JS-123)

  9. #9

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    True, I did realize he was wanting DOS at 85hz a few minutes later after making my post, but I still wanted to link this tool just because it exists.
    Join your local penny pincher movement today!

  10. #10

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    Pfft, the eyestrain and headaches were part of the full CRT experience :P

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