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I bought a pair of these from ebuyer for £10.99 each because they had an excellent review on there and one of the comments was that they work straight out of the box on an XP machine. They don't. I plugged them in to the computers and turned on- neither machine recognized it even though they are both running Windows XP Service Pack 3. So, I looked in the manual- DO NOT INSERT CARD WITHOUT INSTALLING DRIVERS FROM THE CD! So, I tried putting the CD in and Windows found the drivers on there for the cards but there was a huge list. On my Dell PC I selected a random one from the list (they were all identical) and it worked perfectly. On my MSI board PC this strategy didn't work at all. It took me a long time to uninstall the card properly and install the software on the CD before inserting the card. This was because I found after several attempts I had to resort to using System Restore to get my computer into a state where the proper install procedure would work. So lesson learned is to READ THE INSTRUCTIONS!!!
So now they are working fine and they are very fast. I saw great speed improvements over my 100MBPS cards. All of my testing was done using windows file sharing, shared folders, using CAT6 VIDEK cables and a Netgear GS105 and using Task Manager's networking tab to gauge the data speed. The speed improvement depends on a lot of things. Firstly I found that if you initiate the copy and paste of files over the network from the fastest machine it is a lot faster. It is also faster to write to a slow hard drive than to read from it. So my speed improvements ranged from about 5% to 250% increases in speed.
I consider this to be well worth it since I already had one computer with two Gigabit ports built in and now all three can transfer on the Gigabit network. This means I can back them all up quickly and easily. I think backing up to another computer is the easiest and most practical solution for storing data.
The cards came with the usual PCI back plates attached but also low profile ones too which could be useful in certain situations. They also come with INSTRUCTIONS and a Wake-on-LAN cable. This connects to pin headers on the card and the other end presumably connects to compatible motherboards. I could not find any mention of this feature in the instructions (apart from the packing list) so I didn't use it.