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Matt Ross 2005-02-08 00:41
When I replace my PC in the next few months I would like to go the 2 monitor route. My primary will be a 20" CRT [because it's still very good quality] maybe upgrading to a nice 20" TFT in the future. The secondary will be a 45" DLP TV with HDMI/DVI input. Primary will be 1600x1200@85Hz and secondary will be 1280x720@50/60Hz.
Will one dual DVI card handle both these simultaneously or should I be looking at 2 PCIexpress cards?
I alse see from other posts here that if I go the 2 card route then I can't have SLI and still be able to switch modes and use both cards independently [having my cake and eating it!] Is there ever likely to be a way of switching these modes on-the-fly with some kind of software-controlled smart SLI connector?
Thanks.
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Slackmaster K 2005-02-08 07:42
That would work. To figure out how much you can handle, multiply horiz by vert resolution by color bpp. That's how much video RAM you need. All other configuration is just symantics and disabling limitations under advanced config. For example, your config comes out to ((1600x1200)+(1280x768))*32. That is:
1600*1200 = 1,920,000
1280*720=921,600
Total pixels = 2,841,600
Bits per Pixel = 32 (true color)
Total Video RAM required: 90,931,200 (86.7MB)
This is per videocard, thus when you grow and start adding more, you'll figure them independently. Unfortunatly, most video cards running dual screens split the memory evenly, thus a 128mb card becomes two 64mb cards as opposed to logical addressing - unless you run pan mode. An example of my system:
VC1: 128MB (2x 1600x1200x32 = 117.2MB used)
VC2: 64MB (1x 1920x1200x32 = 70MB used)
VC3: 64MB (1x 1920x1200x32 = 70MB used)
How, you ask, does 70MB fit onto a 64MB card? An outstanding question. Oddball resolutions such as 1920x1200, 1280x960, and 1152x864 are designed for alternate display type such as TFTs, plasma, or LCDs. When used on a CRT (the big monitors with fat asses) and the CRT doesn't recognize the mode, it switches to the next lower resolution and emulates the higher resolution with the extra colors. Thus, 1152x864x32 is actually 1024x768x32 but you only see 24 bits' worth of color even though you can't visually see a difference. Thus, 70MB becomes 58.6MB which easily fits into 64MB.
Just a few new things you never knew you needed to know.
Video RAM:
Slackmaster K
kevin@idxt.biz
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ECarlson 2005-02-08 10:46
That should work fine on one card, but if you plan to upgrade the CRT to a DVI LCD someday, some cards have limitations on their max DVI resolution, expecially when driving 2 displays. Also, finsing a dual DVI card is not as easy as finding a card with DVI and VGA.
Also, Slackmaster K forgot to divide by 8 (bits in a byte), so only 1/8th of that amount of video RAM (11,366,400 bytes) is required for that total resolution in 2D, but additional memory is used for 3D effects.
- Eric, www.InvisibleRobot.com
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Matt Ross 2005-02-08 21:11
Thanks for your help and the descriptions of video ram usage. My main concern was how a high res on one would affect the quality of the other. Things have no doubt moved on since my current card, which has TV out as its secondary output and is horrible on my monitor when I activate the TV out. It only works well if I disable the primary monitor while using it TV out.
Whatever I buy will probably have 256MB anyway. I tend to favour Nvidia cards so I will more than likely draw up a shortlist of dual-DVI choices.
On another note has anyone here got that newish 20" Viewsonic TFT [VP201 I think]? The reviews I've seen have been quite good but I'd rather hear from some real users. Price seems remarkably good for the specs.
Thanks.
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