A x16 slot is a PCI-express full length slot.....you usually slot video cards into this slot(which are PCI-express of course)....the PCI-e x1 slot is sort of an "expansion" slot for smaller PCI-e cards(Like the Nvidia "Physx" physics processing card that NVidia released awhile back to work with some games.), and plain old PCI slots are for older components like ethernet cards/sound cards/old modem cards/etc.
Usually the better version the PCI-e x16 slot has(1.0,1.1,2.0, etc) the faster the slot and the quicker it can send data between the card and the rest of the system......this allows for using better video cards in higher resolutions when playing games and video/etc. Of course one should ALWAYS make sure the card they pick:
A: Is a pci-e version card that can work with/is compatible with your motherboard.
B: Is Rated to use less power than they currently have via their PSU
C: Can physically FIT into the system atop the motherboard(some cards are very long/wide and can be blocked from being slotted into the pci-e x16 slot due to the fact that there is other wires/coolers/fans in the way where the card would sit.)
D: (Optional but could be lifesaving down the road) Comes with a good cooling option, preferably one with a nice sized fan/heatsink on the card. (I used a crappy cheap card with a small fan in my case once and because the card was heating up and the fan couldn't handle it it blew the card out over time.....first it would overheat and turn off the system after a set period, and then it wouldn't work at all.)
svmariscal: Well, thanks everyone for this information overload :-p
Now I am pretty sure that I will be fine with almost any low-middleweight card; as I said, I wanted anything just a little better than what I have now. But now I am concerned about this PCIe version thing. I'll see if I can get more information about my motherboard and the possibilities (if any) of patching it.
Thanks again.
EDIT: guys, I've been browsing through Asus online docs and I can't for the life of me find out if my PCIe bus is 1.0 or 2.0 compatible; the only thing I found is that the PCIe version seems to be related to the board chipset, which is Intel 945p in this case. Does that ring a bell to anyone?
As most cards I have found are 2.0 (which seems to be the standard now) what if I buy one of those and plug it in a 1.0 slot?
spinefarm: "two PCI Express x16 slots, one PCI Express x1 slot and three PCI slots"
http://www.xbitlabs.com/news/mainboards/display/20050516062735.html Is that even his board? The pic in post 16 shows only 1 pci-e x16 slot, while yours shows 2.
svmariscal: Thanks, but I had the impression that the x16 relates to the physical slot, and the 1.0/2.0 thing (which is not mentioned there) had something to do with the BIOS version or the like. Am I right? (probably not :p)
Read the post above to Dubconqueror......I list some info about each kind of slot. :)
I will look into your board some more and try to help in a bit if I can....brb.
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Edit: It seems from what I can tell(looking at the release dates for your board[estimated] and the release dates for the various PCI-e versions) that your board is the older PCI-e 1.0 spec...and is thus incompatible with any PCI-e version over 2.0
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One suggestion: Card is a 512 Mb GT 440(geforce card) using DDR5 ram for 69 bucks plus shipping.....the benchmarks put it at around twice the speed of your old card:
link I also found other cards with more ram(1GB) but they use the slower DDR3 ram spec. so IMO they aren't worth it, plus you said you mostly play older games so 512 should be more than enough.