Re: monitors & video cards (was: JPS?)

[P3D John W Roberts <roberts@xxxxxxxxxxxxxxxxx>]

>Date: Mon, 28 Apr 1997 23:27:55 -0500
>From: P3D Andrew Woods <andrew@xxxxxxxxxxxxxxxxxxxxx>
>Subject: Re: monitors & video cards (was: JPS?)

>I wrote:
>>The maximum refresh rate that a particular video card can generate
>>for a specified resolution (640x480, 800x600, 1024x768) in either
>>interlaced or non-interlaced format is determined by the maximum
>>pixel rate of video card.

>John Roberts wrote:
>> And by the maximum horizontal sweep rate (if you want to fill the screen),
>> and by the minimum horizontal and vertical retrace times / blanking intervals.

>These are both set by the limitations of the monitor.

Agreed. So the maximum refresh rate you can show under a given set of 
conditions depends on a number of factors connected to the graphics card
and the monitor.

>> Also in some cases by the amount and speed of video memory available, and
>> the number of colors you want to show.

>The amount of video memory available will determine the maximum resolution
>for a particular colour depth - but it won't affect the maximum refresh
>rate.  The speed of the video memory will be linked with the max pixel
>rate of the video card.

I don't think that's the most useful way of looking at it. The ATI-264VT
(chosen because I was able to borrow the specification quickly) will display
with a refresh rate of 120 Hz at various resolutions (up to 1024x768) and 
color depths, but only if there's 2MB of DRAM on the board. With only 1MB 
of DRAM, the maximum refresh rate is 100 Hz for 640x480 and 800x600, and 
75 Hz for 1024x768.

And for a 1MB board at 640x480 resolution, you can display with a refresh
rate of 100 Hz at up to 16 bits color depth, but only at 75 Hz and slower
at 24 bits color depth. So amount of video memory available and number of
colors shown sometimes *do* affect the maximum refresh rate.

John R


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