ATI’s Radeon HD 3870 X2 series pairs two R670 GPUs
together. Each CPU is made on the 55nm process, and the chips containing a
rather ominous 666 Million transistors. By the numbers, the R670 feature 320
stream processors, 16 raster operation units and 16 texture units. Core clock
speed is 775Mhz, though the HD 3870 X2 increases this to 825Mhz, and memory
speed is 2.25GHz DDR (again the HD 3870 X2 has different memory numbers, see
below for more info on this matter).
Functionally, the twin R670 chips on the MSI
R3870X2-T2D1G-OC co-operate just as if they were on two separate video cards in
two separate PCI Express slots. This is possible due to the fact that the
Crossfire logic is actually built directly into the die of the R670 GPU.
Each R670 chip simply requires a means of transferring
the necessary synchronization data to any other compatible GPUs. The HD 3870
X2’s design provides an internal PCI-Express switch (based on the PCI Express
1.1 standard, so capable of a maximum of 4GB/s bandwidth) which connects the two
cores and carries data in and out of the card. Each GPU has access to a dedicated 512MB of video memory.
ATI has designed the HD 3870 X2 to use DDR3 memory,
rather than the faster DDR4 memory used in the standalone HD 3870 reference
cards. Why this should be is not really clear, as ATI's next-generation dual
R770 (HD 4870 X2) design uses DDR5 memory… Possibly the interconnects on the
3870 part necessitate slower and more stable video memory, while the faster
connections are better suited to the HD
On the other
hand, the HD 3870 X2 sets the default clock speed of
its twin GPUs 50Mhz higher than the stock Radeon HD 3870.
Microsoft’s newest graphics API, DirectX 10.1
is fully supported by the Radeon HD 3870 and HD 3870 X2. Also
included in the HD 3870 X2’s feature set are additional HD video display
features designed to enhance blu-ray video playback better. This brings the
videocard's hardware enhancement features
in line with the new features offered by the latest iterations of the newly triumphant
blu-ray video standard.
ATI/AMD's CrossfireX feature is supported, of course,
with provisions for up to four GPUs; 4 x single GPU video cards or 2 x dual GPU video cards. The Radeon HD 3870 X2 is only compatible with
other video cards in
the 38xx series, sadly. Next up, some serious power consumption values...