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Best LJ brains... [Sep. 16th, 2008|05:33 pm]
So, to celebrate my new employment with Microsoft, I did something I'd been aching to do for a while... I bought a new set of computer components and built myself a new PC.

(AMD dual core 2.9ghz - I wanted a quad core, just because, you know, they exist, but then I had to choose energy usage, and 65 watts seemed too attractive to me... 95 and 125+ were just too high for a PC I'd like to have running 24x7. So I had to choose between quad core at 1.8ghz, or dual core at 2.9. Now, yes, 4x1.8 is bigger than 2x2.9, but unless I'm running multiple threads simultaneously, the extra cores won't be used, so 2.9 it was.)

(Okay, okay: 4 gigs dual channel 1066 memory, but restricted to 800 because I'm not using the latest and greatest AMD CPU. Windows XP 32bit for now; it's what I had available - and plus, with only 4 gigs of memory, there's no compelling reason to go 64bit yet. 500 gig SATA hard drive. I'm hoping to go to RAID someday, but I figured it wasn't worth it yet.)

Now for the questions.

First, my motherboard seems to have decent video capabilities. Looking at DVI connectors, I have the DVI-I Dual Link.

Does that mean with a splitter I can hook two monitors to this? I've seen such setups before, I know they're possible, but I don't know if this is, in fact, the right hookup (even though the "dual link" strongly suggests it is). And, are DVI cables expensive? I've seen some hideously expensive ones, but I don't know if they weren't like high priced cat-5 cable... the same as the cheap stuff, more or less, but they think some sucker will pay the higher prices.

Second: How does one go about measuring video performance? If, e.g., I want a PCIe video card for this, how do I check to see that I'm not actually connecting something slower to my machine?

And does anyone know anything about interactions between multiple video cards? I assume that I'd always want to run the most video-intensive thing to the most powerful card (i.e., run it on the monitor attached to that card), but is there anything funny that happens when you mix video cards up?

e.g., if you have a high speed disk drive, you never put it on the same channel as a low speed CD-ROM when using ATA connectors. The CD-ROM can slow down the entire channel (or so they say - I've heard conflicting opinions and never tested it myself). Is there anything like that with video, where if I put a slower video card in my PC, it could slow down the on-board video?

[User Picture]From: brooksmoses
2008-09-17 05:36 am (UTC)
My experience is that DVI cables aren't that expensive -- they are, after all, digital signals, so it's not like VGA where quality makes a visible difference....

As far as I know, you won't slow down the video by adding a slower card. As I understand it, the thing that happened with ATA connectors is that the signals could go over the cables at different speeds, but the same communications link went to both drives on the cable, so they have to both talk at a speed they can both understand -- so, if you have one drive that speaks ATA100, and one that speaks ATA33, they'll both talk ATA33. (Note that this only affects raw line bandwidth to the drive, not other things like seek speed or such.) With PCI-E, each device gets its own communications link, and that's at a fixed speed anyway.

There are benchmarks for video speed; I don't know anything about them, but most good reviews (e.g., Tom's Hardware) quote numbers from them. Note that there are multiple dimensions of "video speed", too -- I assume you're asking about rate of drawing 3D objects in games, which is what's usually measured, but rate of drawing 2D objects for scrolling windows can be relevant too, though anything these days should be "quite fast enough" with that.
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[User Picture]From: johnpalmer
2008-09-26 03:29 pm (UTC)
(After a long delay...) Thank you for the help!

Re: cable cost, I think it's that there are plenty of people out there glad to take extra money for cheap cables if they can get it :-).

The ATA stuff is what I thought I understood, but I didn't know the PCIe stuff avoided the issue... I haven't kept up on hardware as well as I could have. But I'd heard some folks saying you shouldn't mix a CD-ROM and a hard drive at all, and I thought that sounded wrong, but I couldn't disprove it.

And thanks for the pointers re: video speed; I'll do some more searching.
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From: gh4acws
2008-09-17 10:49 am (UTC)

what I have heard

is that that different speed on one cable WAS a problem when the respective drives were using PIO (1 to 5 ) but not for the newer UDMA ( 33/66/100/133 ). Since these days the older PIO system is not used anymore ( well recently I tested an old 2x CD-Rom drive THAT one was using PIO ) this is not a concern.

Video: from what I gather from the mags : several Videocards sharing the PCIe bus may have to share some resource ( lanes) so one can have one with 16 or two with 8 - or with a different chipset one with 16 but the second card will only get 4 . For this it might be useful to know what model your motherboards is actually. ( IF by chance it was tested within the last year I can look up what they said - and then one can check for a better BIOS and drivers with the maker )

Two monitors : this may depend a lot on what you plan to do with those :
For quite a lot of obvious applications an uneven split in video power would be normal : application on powerful screen 1 and sourcecode in 'text-mode' on screen 2.
Or view from the cockpit on screen one and instruments on screen 2.

The way I read it DVI-I dual plug on your motherboard will be able to drive a big screen - possibly with the right drivers for the onboard graphics also supply a split screen. ( but you probably had that figured out anyway )
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[User Picture]From: marypcb
2008-09-23 03:15 pm (UTC)

Re: what I have heard

dual-link DVI is indeed two DVI streams so that you get enough data to drive the humongous resolutions on a 30" monitor (the only models I know of with dual-link DVI connections) - there are splitter cables to drive two screens but reviews are mixed (http://www.amazon.com/Cables-Unlimited-DVI-D-Splitter-PCM-2260/dp/B000H09RFM) and you need virtually identical monitors and may end up mirroring rather than extending the desktop. The real tool is a DVI switch but then you're up to the cost of a graphics card anyway

the usual way to do twin monitors is with a graphics card that has two ports - almost all do, but many are one VGA and one DVI and while it's easy to connect a DVI port to a VGA monitor it's not as easy to go the other way, so check first. Once you have the card, Windows lets you extend the desktop very simply - graphics options shows two screen icons you can drag into position. Typically the presence of the discrete graphics card automatically disables the lesser onboard graphics - laptops that switch between onboard and discrete SLI graphics do it either by rebooting the PC or better the graphics driver or, on Sony, by loading both graphics drivers into memory and having a shim driver that calls one or the other depending on the power mode you've chosen. The main use I know for a two-graphics card machine would be for CUDA gpu computing, or for letting you use both AGP and PCIe - but unless you're doing serious animation rendering I'm not sure of the need

if you don't want to get a dual-headed DVI graphics card look for the DisplayLink kit from people like Kensington and Belkin - this drives up to six monitors over USB at 1620 resolution per screen - and there are wireless USB versions.

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[User Picture]From: johnpalmer
2008-09-24 12:14 am (UTC)

Re: what I have heard

Well, I found part of the problem. There are machines with proprietary dual-DVI ports on them. I hadn't been able to look at them, so all I remembered was that they didn't have a standard DVI pinout, but I just got to see one again today, and it doesn't look anything like any of the DVI ports on the Wikipedia page.

So, that was a large part of my confusion.

I probably will end up going for a dual head video card, now that I understand what's going on.
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