The Trials of Overclocking

Some cards embrace overclocking with open arms but there are a few things about overclocking the HD3870 X2 that you should be made aware of. First of all there is the little caveat of the power connectors.


Like with the HD2900XT, there is one 6-pin and one 8-pin PCI-E connector on this card. We tried a few combinations to see if it was possible to overclock with a pair of 6-pin connectors plugged in and these are the results we got.


On the left we see the ATI Overdrive option that comes up when both the 8-pin AND the 6-pin PCI-E connectors are installed. Meanwhile, when only two 6-pin connectors are plugged there is no Overdrive option though the card operates perfectly normal at stock speeds in any game. There are ways around the need for an 8-pin connector for overclocking and if you need any pointers for this, please feel free to post on the HD3870 X2 comment thread in our forums.

Even with the 8-pin connector installed, overclocking didn’t go very far with this engineering sample.

Max Overclocks:

Core: 865Mhz
Memory: 1892Mhz (DDR)

These clocks represent a pretty pathetic overclock of 50Mhz on the cores and 92Mhz on the memory. Considering the GDDR3 memory is rated at 2Ghz (DDR) I would think that either ATI tightened the timings or there is insufficient voltage running to it to facilitate higher overclocks. The core is another matter altogether; all signs point to the dreaded issue that plagued the early HD3870 512MB cards which couldn’t clock past the 862 to 867Mhz mark. These cards needed a BIOS flash in order to overclock past that point but flashing the BIOS on this card with two GPUs is a bit beyond the scope of this review. It is possible that this is an issue with our engineering sample and won’t carry into the actual production cards.


As you can see, these minor overclocks net us less than 200 points in 3DMark06 and would provide next to no performance increase in games. Also, as we discussed before you have to overclock both GPUs and memory separately like you would in a dual card Crossfire setup. The process goes something like this:

1. Overclock GPU #1
2. Overclock memory associated with GPU#1
3. Test Clocks
4. If overclock passes, accept Overclock
5. Overclock GPU #2
6. Overclock memory associated with GPU#2
7. Test Clocks
8. If overclock passes, accept Overclock

ATI should make things easier by just allowing one GPU to determine the clocks of the other. It would simplify all our lives.