Adrian Chadd wrote:
Next - refresh rate. Its a fun one. refresh rate affects CRTs by just overtaxing what the electronics and the tube itself can do. Refresh rates can limit LCD resolutions by trying to push too much data over DVI. DVI has a fixed upper speed and doesn't fail gracefully like VGA (read: blurring and artifacts.) This is why you need >1 DVI connector to drive those enormous apple monitors - because one DVI connector couldn't support the data rate needed to drive that resolution at the refresh rate.
err, you still use 1 DVI connector for the 30" apple displays... They're special in a different way. Conventional "Single-link" DVI is limited to a dot-clock of around 165MHz. This basically caps you to a maximum (standard) resolution of 1920x1200. To get around this to allow the larger, very high resolution monitors, a standard known as Dual-Link DVI was created. Dual-Link DVI uses a second set of digital data connectors on the _SAME_ DVI plug to drive the display. It's still one connector, but it's two digital channels. Also with refresh rate, it's the 'maximum bandwidth' figure (which you'll find in your CRT monitor manual) which limits the maximum dot-clock. (VGA itself, being analogue, has no real limit as to the maximum dot-clock, the only limits are the card generating the signal and the ability of the cable being used to clearly carry the signal without interference). Some monitors also limit the Hsync and Vsync speeds. Dot clock is directly related to the product of the refresh rate and resolution, that is: dotclock = refreshrate * hres * vres where refreshrate is in Hz and hres and vres are in pixels and include the blanking delay (usually an additional 10% for CRTs, much less for LCDs - these are the 5th and 9th number in a modeline respectively). So, for a 1280x1024 @ 85Hz on a CRT: 1280 + 10% -> 1408 1024 + 10% -> 1126 Dotclock ~= 1408 * 1126 * 85 = 134759680Hz, or ~135MHz. By similar math given the dotclock and resolutions, you can calculate the refresh rates: href = dotclock/hres vref = href/vres where vref is the vertical refresh rate and href is the horizontal refresh rate, both in Hz. C. -- SLUG - Sydney Linux User's Group Mailing List - http://slug.org.au/ Subscription info and FAQs: http://slug.org.au/faq/mailinglists.html
