Why does refresh rate affect screen width?

[Yossarian]

I have a Samsung Syncmaster 900NF w/a Gainward GeForce 3 Ti200. If I set the refresh rate to 120 Hz (1024 x 768), the visible screen area fills the full monitor width. Without making any monitor adjustments, if I then set it to 75 Hz, there's about 1/2" of black on the left and right. In other words, the visible screen area is less wide than the monitor allows. Why is this?

Also, I get a noticeable flicker at anything up to about 100 Hz. Is my monitor dying?

 

[imgod2u]

When you're running at 1024x768, you'll need to draw 768 lines every 1/60th of a second for 60 Hz and every 1/120th of a second for 120 Hz. If you raise the resolution up to 1280x1024, you'll need to draw 1024 lines every 1/60th of a second for 60Hz and every 1/120th of a second for 120Hz. Obviously it's harder for the monitor to draw 1024 lines that fast than to draw 768 lines. Also, the 350MHz RAMDAC (which converts the digital signal into an analog image signal) has its limitations as far as how many lines it can convert and send every 1/60th of 1/120th of a second. All this is moot on an LCD as there is no such thing as a refresh rate and since it's all digital, the only limitation is the pixel response rate.

 

[MCS]

I have the 900NF and I don't see any flicker at 85Hz.

 

[FalseChristian]

All monitors display the phenomena you're talking about. My does. You just have to set the screen up using your vertical and/or horizontal controls and Windows will remember it. No need to worry about it again until you have to reinstall Windows.

 

[Gosharkss]

A monitor has three timing components, the pixel clock (Mhz), the horizontal refresh rate (Khz) and the vertical refresh rate (hz).

The pixel clock is the amount of time it takes to draw on pixel on the screen.. The horizontal refresh is the time it takes to draw one line. The vertical refresh rate, also called the vertical frequency, vertical scanning frequency, or simply refresh rate, is a measure of how many full screens the monitor draws per second and is given in hertz (Hz).

When you increase the refresh rate both the horizontal refresh and the pixel clock increase. In order to draw frames faster you must draw lines faster, which means you must draw pixels faster.

For example: 106Khz Horizontal is the standard VESA timing for 1600 x 1200 at 85Hz. Pixel clock at this timing is 229.5Mhz. The monitor has screen geometry setting stored in its memory standard VESA timings.

When you change the resolution these numbers change. There is no VESA standard timing for many of the resolutions above 85Hz. When the monitor receives the signals (above 85Hz) from the video card it does not know what to default to. In some cases this leaves a large border or other geometric distortions on the screen.

 

[Pauli]

The bottom line is that you will most likely need to adjust your monitor dimensions every time you try a new "Video Mode". The video mode will change each time you change either the resolution (e.g. 1024x768), refresh rate, or color depth. Modern monitors attempt to "Auto-sync" with each video signal change and they "remember" the settings for each if they have been changed. They only need a little fine tuning to get them to fill the whole screen without distortion.

I guess LCD panels do not have this problem because they don't work the same way as CRTs (I don't know much about these). But today's CRTs are much, much, better than the CRTs of 15-20 years ago, when multi-sync monitors were very expensive compared to the standard displays that were only capable of 640x480 resolutions. My first multi-sync monitor was 15" and cost $700.

 

[Yossarian]

Interesting, thanks for the informative replies. I was hoping the "monitor guy" would show up

I guess it's a problem with the monitor then regarding the flicker at lower refresh rates since I got it with 2 different video cards and a variety of Nvidia drivers.