Using a PCI Express 1.1 bridge chip between the two HD 3870 GPUs seems like an odd move as it would appear to be a bottleneck in performance. Nvidia did something similar with its nForce 780i chipset as most of the PCI Express is controlled by an nForce 200 chip which also supports PCI Express 1.1, so it's clear that both AMD and Nvidia feel that the older standard has plenty of bandwidth headroom at present.
One change for the X2 compared to the HD 3870 is the addition of a second power connector. Just like the old HD 2900, there’s one six-pin and one eight-pin connector, and while you can use a pair of six-pin PCI Express connectors this has a downside. If you want to use the Overdrive part of the Catalyst drivers to overclock your X2 then you need to use an eight-pin feed. Your reviewer has a fair few high-end power supplies kicking around, among the, three that have four six-pin connectors for all manner of SLI and CrossFire configurations but none has an eight-pin connector for the graphics. The odds are that you’re in the same boat, so if you’re considering an X2 and fancy a spot of overclocking then you’d better budget about £150 for a new, suitable power supply.
Installing the X2 was an absolute doddle as the CrossFire element is permanently enabled so you plug in the card, install the drivers - beta in this case - and you’re good to go.
We tested the Sapphire card on an Abit IP35 Pro with an Intel Core 2 Q6600 processor and 2GB of Corsair memory all running Windows Vista Ultimate Edition. In an ideal world, we’d have compared the X2 with an HD 3870 but we didn’t have one to hand. What we did have, however, was a pair of PowerColor HD 2900 XT cards. These boys deliver the same performance as the HD 3870 although they consume far more power. The comparison isn’t completely fair as the PowerColors have 1GB of memory on each card instead of the usual 512MB but it's close enough to act as a useful test.
Driver issues ...
I had two ATI cards in the past (7500 and 9500 based). Unless things have changed - you'll be waiting a long time for ATI to "straighten out" the drivers, because they didn't do a very good job back then, with (supposedly) "release) drivers.
One of the reasons I switched to nVidia. Haven't had nearly the driver agony since.
(I know some will say "That's all fixed now!" - but, well, it wasn't fixed when I had the cards. That whole thing about leaving a lasting impression ...)
I use a number of displays for testing including 19 and 24 inch TFTs but I also have a Taxan EV2285 CRT with a max resolution of 2048 x1536 which of course uses an analogue connection but it sure does look pretty.
Do the Reg guys hook up a massive old CRT monitor to do the test at 2048 x 1536?
@ Alastair and Brian
Nvidia fan? oh please. Most high-end power supplies have a bunch of six-pin PCIe connectors but eight-pins are rarer than a rare thing. If you can provide a couple of make and model numbers that are appropriate to overclock the X2 then I'll eat my words.
Brian and Bus bandwidth: in principle you are correct with a great big 'However'
I don't know how much bandwidth a PCIe graphics card requires. I know the speed of PCIe 1.1 and 2.0 and how many lanes the various PCIe slots provide but I don't know how much bandwidth, say, a GeForce 8800GT requires. The Intel P35 chipset only supplies four lanes of PCIe 1.1 to the second graphics slot which is one quarter of the main slot and one eighth of the bandwidth of the PCIe Gen 2.0 slots you'll find on the latest crop of motherboards but even so it seems to be adequate in most cases.
Turning that the other way round a pair of HD 3870 cards in a single x16 slot a la X2 is the equivalent of eight lanes of PCIe per chip provided the bridge chip and drivers do their jobs correctly, in which case I doubt the graphics slot will be the bottleneck in performance.
I find it hard to believe that the reviewer has obviously overlooked the fact that this card is only supported by a single x16 PCIe slot, thus creating a bottleneck when the card is pushed to the limit.
The 2x 2900XT's have at least 1 x 16xPCIe +1x 8x PCIe slot creating 150% of the bus bandwidth to play with for highly intensive graphics.
I may be mistaken, the 2 x 2900XT's may have 2 16x PCIe's further improving bus throughput.