XFree86 Video Timings HOWTO : Basic Things to Know about your Display and Adapter : The monitor's video bandwidth:
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## 4.1. The monitor's video bandwidth:

If you're running XFree86, your server will probe your card and tell you what your highest-available dot clock is.

Otherwise, your highest available dot clock is approximately the monitor's video bandwidth. There's a lot of give here, though --- some monitors can run as much as 30% over their nominal bandwidth. The risks here have to do with exceeding the monitor's rated vertical-sync frequency; we'll discuss them in detail below.

Knowing the bandwidth will enable you to make more intelligent choices between possible configurations. It may affect your display's visual quality (especially sharpness for fine details).

Your monitor's video bandwidth should be included on the manual's spec page. If it's not, look at the monitor's highest rated resolution. As a rule of thumb, here's how to translate these into bandwidth estimates (and thus into rough upper bounds for the dot clock you can use):

> `

>     	640x480			25
>     	800x600			36
>     	1024x768		65
>     	1024x768 interlaced	45
>     	1280x1024		110
>     	1600x1200		185

> `

BTW, there's nothing magic about this table; these numbers are just the lowest dot clocks per resolution in the standard XFree86 Modes database (except for the last, which I interpolated). The bandwidth of your monitor may actually be higher than the minimum needed for its top resolution, so don't be afraid to try a dot clock a few MHz higher.

Also note that bandwidth is seldom an issue for dot clocks under 65MHz or so. With an SVGA card and most hi-res monitors, you can't get anywhere near the limit of your monitor's video bandwidth. The following are examples:

> `

>     	Brand				Video Bandwidth
>     	----------			---------------
>     	NEC 4D				75Mhz
>     	Nano 907a			50Mhz
>     	Nano 9080i			60Mhz
>     	Mitsubishi HL6615		110Mhz
>     	Mitsubishi Diamond Scan		100Mhz
>     	IDEK MF-5117			65Mhz
>     	IOCOMM Thinksync-17 CM-7126	136Mhz
>     	HP D1188A			100Mhz
>     	Philips SC-17AS			110Mhz
>     	Swan SW617			85Mhz
>     	Viewsonic 21PS			185Mhz

> `

Even low-end monitors usually aren't terribly bandwidth-constrained for their rated resolutions. The NEC Multisync II makes a good example --- it can't even display 800x600 per its spec. It can only display 800x560. For such low resolutions you don't need high dot clocks or a lot of bandwidth; probably the best you can do is 32Mhz or 36Mhz, both of them are still not too far from the monitor's rated video bandwidth of 30Mhz.

At these two driving frequencies, your screen image may not be as sharp as it should be, but definitely of tolerable quality. Of course it would be nicer if NEC Multisync II had a video bandwidth higher than, say, 36Mhz. But this is not critical for common tasks like text editing, as long as the difference is not so significant as to cause severe image distortion (your eyes would tell you right away if this were so).

XFree86 Video Timings HOWTO : Basic Things to Know about your Display and Adapter : The monitor's video bandwidth:
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