PCI Express comes in two speeds. PCI Express Rev 1 is 250MB/sec per lane.
PCi Express Rev 2 is 500MB/sec per lane. Rev 2 is compatible with Rev 1.
If a Rev 2 device is plugged into a Rev 1 slot, it is supposed to run
at Rev 1 speeds.
There are very few PCI Express x1 slots running at Rev 2 speeds. The
majority today are Rev 1.
You should take a careful look at your friend's computer, and see
what spare slots are available. PCI Express x1 is better than PCI,
250MB/sec versus 133MB/sec. Buying a PCI video card might be
an option, but not the best option.
The computer may also have an AGP slot, and there are still AGP
video cards. The newer cards use a bridge chip, Rialto for ATI
cards, HSI for Nvidia cards. The bridge chip converts a PCI
Express GPU, to work with an AGP slot. The best support might
be for AGP 4x or 8x slots, as the bridge chip may only run at
1.5V. If you have a really old motherboard (like my 440BX motherboard),
it has a 3.3V AGP slot, and the newer AGP bridged cards probably
wouldn't fit into the slot (the 3.3V key would prevent it).
Info on fitting AGP cards is here.
http://www.playtool.com/pages/agpcompat/agp.html
Summary:
1) PCI Express x16 slot - 4GB/sec or 8GB/sec bandwidth. Would work with
modern PCI Express video cards of either revision. Only a couple
cards had issues, when Rev 2 first came out. They should all work now.
2) PCI Express x1 - harder to find replacement cards. 250MB/sec
3) PCI slot - the most common slot type, in terms of it being
available in most computers. Some cards are available.
Severely restricted bandwidth, 133MB/sec.
4) AGP slot. 8x = 2133MB/sec 4x=1066MB/sec. 1.5V VIO on those.
(Bridged) AGP video cards may run at 1.5V. Fewer options
for a 3.3V keyed AGP slot, with much older GPUs supporting
that. See Playtool.com for details.
Newegg shows two video cards with PCI Express x1. This one is
low profile, and even includes low profile faceplates for fitting
in a "Dell slim". Fan is noisy. Card is expensive at $105.
Card may accept an after-market heatsink and fan, if a better
cooler is desired.
http://www.newegg.com/Product/Product.aspx?Item=N82E16814161280
Post the make and model of computer, if you need more assistance.
Also indicate what slots are occupied or are empty.
*******
A PCI Express x16 card could fit into an x1 slot... if the end
of the slot was cut off
Surgery would be risky, and involve
a Dremel.
The orange slot here, is an "open ended" x4 slot. It will accept
an x16 card. This is a picture of a motherboard, where the slot
installed on the computer, is open on the end on purpose.
http://www.hothardware.com/articleimages/item830/big_12.jpg
The x4 slot (top one) here has the more normal "closed end" and only
a x1 or x4 card will fit. Dremeling out the bir on the end, could
make it "open ended" - assuming the connector doesn't spring apart
too much.
http://upload.wikimedia.org/wikipedia/commons/f/fc/PCIExpress.jpg
In theory, a PCI Express x16 card can operate at x16, x8, x4, x2, x1.
But experience varies as to how a card will respond if plugged into
some of the lower end options. For example, my motherboard has
x4 wiring of a x16 slot, and not all video cards will work in
it. So while grinding the center section out of the end of the
PCI Express x1 connector would make more card options available
to you, I can't promise all the cards will work without issue.
The "x16, x8, x4, x2, x1" thing was tested here.
http://www.tomshardware.com/reviews/sli-coming,927.html
HTH,
Paul