An early peek at the Radeon HD 4870 X2

AMD has quite a hit on its hands in the Radeon HD 4850 and 4870, and pretty much everyone already knows it’s developing another product code-named R700, a high-end graphics card based on two 4870s paired together. We have an early engineering sample of this beast, and we can offer a preliminary look at how the card—to be called the Radeon HD 4870 X2—performs. You might be expecting big things, and you might be right. Keep reading to see what we found.

R700 up close

Although this product’s code name, R700, follows a naming convention similar to past high-end Radeon GPUs, it’s not really a new GPU at all. Instead, it’s just two RV770 graphics processors having a party together on one PCB, pretty much like the Radeon HD 3870 X2 was in the last generation. In fact, the new X2 looks an awful lot like the old one at first glance.

The Radeon HD 4870 X2

We don’t have the full scoop on the 4870 X2 at this early date. This is just an engineering sample, not a retail product, and it may be subject to change by the time the boards ship to customers. That’s scheduled to happen some time around the middle of next month, which is soon enough that we don’t expect major changes to the card between now and then.

The board itself is a healthy 10.5″ long, and it sports a couple of PCIe auxiliary power plugs, one 2×4 pin and one 2×3 pin.

Flip it over, and you can see the dual retention brackets for the heatsinks attached to each GPU. Here, if you’re a hopeless geek, you might pause to reflect on the 4870 X2’s likely specs. The RV770 GPUs on our early sample are clocked at 750MHz, the same speed as the regular 4870. As a result, the X2’s 1600 total stream processors have a peak computational rate of 2.4 teraflops. That’s, erm, considerable—beyond the obvious graphics applications, that’s the sort of computing power that may one day enable men to figure out what women want.

Remove the card’s cooling apparatus, and it looks like so:

In the center of the board sits a PLX PCIe switch chip, flanked by a pair of RV770 GPUs. We couldn’t find this particular model of PCIe switch listed on PLX’s website, but when installed, the card shows up as a PCI Express 2.0 x16 device. Each GPU shows up as being PCIe 2.0 x16 capable in AMD’s driver control panel, as well. So our best guess is that we’re looking at a PCI Express Gen2 switch that has 48 total lanes—16 routed to each GPU and 16 connected to the PCIe slot.

Rumor has it the R700 may include a faster GPU-to-GPU CrossFire interconnect in order to help with performance scaling in difficult cases, but we don’t yet have definitive info on how much of a bandwidth boost it may offer.

We do know, however, that the two GPUs on the card don’t share memory. The board has eight Hynix GDDR5 memory chips per graphics processor, four on the front and another four around back. Those chips are 1Gb each, so each GPU has a total of one gigabyte of memory to call its own. Cumulatively, 4870 X2’s effective memory size is still 1GB, since data must be replicated into each GPU’s memory space.

Although the Hynix chips on our engineering sample are rated for up to 4Gbps operation, on this board, they run at the same 900MHz base clock and 3600MT/s data rate as on the Radeon HD 4870. That ain’t exactly shabby, though. All told, the R700 has an aggregate 512-bit path to memory that theoretically peaks at 230GB/s. To put that into perspective, its likely closest competitor, the GeForce GTX 280, has “only” 142GB/s of peak memory bandwidth.

With that in mind, the big question about the 4870 X2 is: How does it perform? If you’ve answered “About like two Radeon HD 4870s in a CrossFire setup,” you’re on the right track. Compared to a dual-card config, this puppy has the potential benefit of a faster CrossFire interconnect between the GPUs and twice the effective memory size (single 4870s currently have 512MB), but it has the possible disadvantage of those GPUs having to share PCI Express bandwidth to the rest of the system via that PLX switch. Which, of course, is why we test these things….

Our testing methods

As ever, we did our best to deliver clean benchmark numbers. Tests were run at least three times, and the results were averaged.

Our test systems were configured like so:

Processor Core 2 Extreme QX9650 3.0GHz Core 2 Extreme QX9650 3.0GHz
System bus 1333MHz (333MHz quad-pumped) 1333MHz (333MHz quad-pumped)
Motherboard Gigabyte GA-X38-DQ6 EVGA nForce 780i SLI
BIOS revision F9a P05p
North bridge X38 MCH 780i SLI SPP
South bridge ICH9R 780i SLI MCP
Chipset drivers INF update
Matrix Storage Manager 7.8
ForceWare 15.17
Memory size 4GB (4 DIMMs) 4GB (4 DIMMs)
Memory type 2 x Corsair TWIN2X20488500C5D
at 800MHz
2 x Corsair TWIN2X20488500C5D
at 800MHz
CAS latency (CL) 5 5
RAS to CAS delay (tRCD) 5 5
RAS precharge (tRP) 5 5
Cycle time (tRAS) 18 18
Command rate 2T 2T
Audio Integrated ICH9R/ALC889A
with RealTek drivers
Integrated nForce 780i SLI MCP/ALC885
with RealTek drivers
Radeon HD 2900 XT 512MB PCIe
with Catalyst 8.5 drivers
Dual XFX GeForce 9800 GTX XXX 512MB PCIe
with ForceWare 177.39 drivers
Asus Radeon HD 3870 512MB PCIe
with Catalyst 8.5 drivers
GeForce GTX 280 1GB PCIe


GeForce GTX 280 1GB PCIe
with ForceWare 177.39 drivers

Radeon HD 3870 X2 1GB PCIe
with Catalyst 8.5 drivers
Radeon HD 4850 512MB PCIe
with Catalyst 8.501.1-080612a-064906E-ATI drivers
Dual Radeon HD 4850 512MB PCIe
with Catalyst 8.501.1-080612a-064906E-ATI drivers
Radeon HD 4870 512MB PCIe
with Catalyst 8.501.1-080612a-064906E-ATI drivers
Dual Radeon HD 4870 512MB PCIe
with Catalyst 8.501.1-080612a-064906E-ATI drivers
Radeon HD 4870
with Catalyst 8.52-080708a-066515E-ATI drivers
MSI GeForce 8800 GTX 768MB PCIe
with ForceWare 175.16 drivers
XFX GeForce 9800 GTX 512MB PCIe
with ForceWare 175.16 drivers
XFX GeForce 9800 GTX XXX 512MB PCIe
with ForceWare 177.39 drivers
GeForce 9800 GTX+ 512MB PCIe
with ForceWare 177.39 drivers
XFX GeForce 9800 GX2 1GB PCIe
with ForceWare 175.16 drivers
GeForce GTX 260 896MB PCIe
with ForceWare 177.34 drivers
GeForce GTX 280 1GB PCIe
with ForceWare 177.34 drivers
Hard drive WD Caviar SE16 320GB SATA
OS Windows Vista Ultimate x64 Edition
OS updates Service Pack 1, DirectX March 2008 update

Thanks to Corsair for providing us with memory for our testing. Their quality, service, and support are easily superior to no-name DIMMs.

Our test systems were powered by PC Power & Cooling Silencer 750W power supply units. The Silencer 750W was a runaway Editor’s Choice winner in our epic 11-way power supply roundup, so it seemed like a fitting choice for our test rigs. Thanks to OCZ for providing these units for our use in testing.

Unless otherwise specified, image quality settings for the graphics cards were left at the control panel defaults. Vertical refresh sync (vsync) was disabled for all tests.

We used the following versions of our test applications:

The tests and methods we employ are generally publicly available and reproducible. If you have questions about our methods, hit our forums to talk with us about them.

Half-Life 2: Episode Two

We used a custom-recorded timedemo for this game, as well. We tested Episode Two with the in-game image quality options cranked, with 4X AA and 16 anisotropic filtering. HDR lighting and motion blur were both enabled.

The 4870 X2 isn’t quite as fast as a two-card 4870 CrossFire config here, but it’s close, running only a handful of frames per second behind at 2560×1600. Compared to the X2’s intended target, the GeForce GTX 280, it’s not even close. This game scales nicely with multi-GPU setups, and the X2 takes a decisive lead over the GTX 280.

Of course, the GTX 280 also churns out over 65 frames per second at the highest settings tested, so we’re not talking about huge differences in competency when running this game.

Enemy Territory: Quake Wars

We tested this game with 4X antialiasing and 16X anisotropic filtering enabled, along with “high” settings for all of the game’s quality options except “Shader level” which was set to “Ultra.” We left the diffuse, bump, and specular texture quality settings at their default levels, though. Shadow and smooth foliage were enabled, but soft particles were disabled. Again, we used a custom timedemo recorded for use in this review.

Here’s confirmation of what we saw on the previous page. Once more, the 4870 X2 is just a little bit slower than two 4870 cards in CrossFire, but it’s still quite a bit quicker than a GeForce GTX 280. Again, we’re dealing with a game that scales well with multiple GPUs, and again, the R700 comes out looking very strong.


Rather than use a timedemo, I tested Crysis by playing the game and using FRAPS to record frame rates. Because this way of doing things can introduce a lot of variation from one run to the next, I tested each card in five 60-second gameplay sessions.

When playing, I’m on a hillside in the recovery level having a firefight with six or seven of the bad guys. As before, I’ve tested at two different settings, with the game’s “High” quality presets and with its “Very high” ones, also.

These tests involve manual gameplay, so I wouldn’t focus too much on minor performance differences between the cards. For all practical intents, the 4870 X2 ties with the GeForce GTX 280 using Crysis‘ “high quality” presets. With the “very high” presets, the X2 proves to be a little quicker than the GTX 280. In both cases, the X2 performs very similarly to the Radeon HD 4870 CrossFire dual-card config.

Race Driver GRID

I tested this absolutely gorgeous-looking game with FRAPS, as well, and in order to keep things simple, I decided to capture frame rates over a single, longer session as I raced around the track. This approach has the advantage of letting me report second-by-second frame-rate results.

Even a single Radeon HD 4870 is faster than the GeForce GTX 280 in this game, and performance scales pretty well from there with the X2, so that it nearly doubles the average frame rate of the GeForce GTX 280.

This game doesn’t always scale well with multiple GPUs, though. The Radeon HD 3870 X2’s results illustrate that. Even with the latest public driver release for the 3870 X2, Catalyst 8.6, the game doesn’t make use of both GPUs. The Radeon HD 4000-series drivers we’re using are newer and have a CrossFire profile for GRID included. This is the issue, of course, with multi-GPU configurations, including the 4870 X2. Newer games will often require driver updates before the card can live up to its potential.

Power consumption

We measured total system power consumption at the wall socket using an Extech power analyzer model 380803. The monitor was plugged into a separate outlet, so its power draw was not part of our measurement. The cards were plugged into a motherboard on an open test bench.

The cards were tested under load running Half-Life 2 Episode Two at 2560×1600 resolution, using the same settings we did for performance testing. At AMD’s request, we’ve omitted power consumption results at idle because this early engineering sample doesn’t yet have its power-saving PowerPlay functionality enabled, so its idle power draw isn’t representative of the final products. That’s unfortunate, because we’re curious to see how the 4870 X2 will do at idle, especially when compared to the incredibly low idle power draw of the GeForce GTX 280.

Going with an X2 instead of two separate 4870 cards will save you a little bit on power consumption, but not much. The X2’s power draw is manageable, but here’s one place where going with two smaller chips instead of one larger chip may prove to be a drawback: the GeForce GTX 280 draws over 100W less power under load.

Then again, this is an early sample, and as I’ve said, PowerPlay isn’t yet enabled. It’s possible AMD may find a way to reduce power use, even under load, in the finished product.

Noise levels

We measured noise levels on our test systems, sitting on an open test bench, using an Extech model 407727 digital sound level meter. The meter was mounted on a tripod approximately 12″ from the test system at a height even with the top of the video card. We used the OSHA-standard weighting and speed for these measurements.

You can think of these noise level measurements much like our system power consumption tests, because the entire systems’ noise levels were measured, including the stock Intel cooler we used to cool the CPU. Of course, noise levels will vary greatly in the real world along with the acoustic properties of the PC enclosure used, whether the enclosure provides adequate cooling to avoid a card’s highest fan speeds, placement of the enclosure in the room, and a whole range of other variables. These results should give a reasonably good picture of comparative fan noise, though.

Our early 4870 X2 sample looks to be part of the trend toward relatively loud coolers in newer video cards, at least under load. Given the amount of power the card consumes and the amount of resulting heat its dual-slot cooler must dissipate, these results aren’t much of a surprise. Subjectively, the X2 does seem to be pretty noisy, although to my ears, the dual GTX 280 SLI rig seemed even louder, despite what our sound level meter said.

GPU temperatures

Per your requests, I’ve added GPU temperature readings to our results. I captured these using AMD’s Catalyst Control Center and Nvidia’s nTune Monitor, so we’re basically relying on the cards to report their temperatures properly. In the case of multi-GPU configs, I only got one number out of CCC. I used the highest of the numbers from the Nvidia monitoring app. These temperatures were recorded while running the “rthdribl” demo in a window. Windowed apps only seem to use one GPU, so it’s possible the dual-GPU cards could get hotter with both GPUs in action. Hard to get a temperature reading if you can’t see the monitoring app, though.

All of the Radeon HD 4800-series cards we’ve tested have produced some relatively high GPU temperatures, and this early X2 card is no exception. When we asked AMD about this issue in relation to the 4850 and 4870 cards now shipping, they told us the products are qualified at even higher temperatures (over 100°C) and tuned for low noise levels. In other words, these temperatures are more or less by design and not necessarily a problem.


I’ve given quite a bit of thought to the issues raised by AMD’s new strategy of pairing up two mid-range GPUs to serve as their only high-end product. I’ve already said that, given the choice in a vacuum between one big GPU to two smaller ones, I’d rather have the single, big GPU. Our experience with the Radeon HD 3870 X2 in GRID is but one example of a problem we’ve seen time and again with multi-GPU cards: without a profile in the drivers, you’re usually stuck running on just a single GPU. Infuriatingly, you’re most likely to run into this problem when playing a brand-new game, right when you want that GPU power the most. Ugh.

However, playing with this early sample of 4870 X2 is a vivid reminder that we don’t make these choices in a vacuum. The reality is that a single Radeon HD 4870 GPU is nearly fast enough to keep pace with the GeForce GTX 280. Even if you’re running a game that lacks a driver profile or simply doesn’t scale well with more than one GPU, the 4870 X2 ought to perform awfully well. And when it does get both GPUs going, as our results show, it’s by far the fastest single video card we’ve ever tested. If this is how AMD rolls, it’s hard to complain.

Of course, now it’s up to AMD to deliver the final product, to price it right, to get its power saving mojo going, and to keep its drivers updated with CrossFire profiles for all of the latest games in a timely fashion. We’d really like to see AMD work more closely with game developers to implement profiles before new games are released—something Nvidia has historically done much better than AMD. One would hope that committing to this dual-GPU path for high-end products would force AMD’s hand a little bit in this regard, but we’ll have to wait and see.

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