AMD unveils Radeon HD 3400, 3600 series GPUs

Just six short months after releasing the Radeon HD 2400 and 2600 series graphics processors, AMD has announced replacements for those chips. The new Radeon HD 3400 and 3600 series GPUs bring a number of refinements, many of which first made their appearance with the debut of the Radeon HD 3800 series two months ago. Like the 3800 series, AMD's new low-end GPUs have also made the transition to a smaller, "half-node" 55nm fab process.

Tops among the changes is support for DirectX 10.1 and Shader Model 4.1, a minor revision to the DirectX spec that offers game developers better control over antialiasing hardware and exposes a new capability, cube map arrays, intended to improve performance with global illumination algorithms. (I wouldn't expect DX10.1 games to set the world on fire with their sheer numbers or distinctive visual glory, but AMD does expect to see games with DX10.1 support hitting the market later this year.)

Many of the other changes simply amount to better plumbing—often necessary but rarely sexy. Among them: support for PCI Express version 2.0, which effectively doubles the bandwidth available between the GPU and the rest of the system. AMD's UVD video processor also gets more bandwidth in this incarnation, allowing the GPUs to accelerate the playback of high-definition video at higher resolutions. And the new chips include native support for DisplayPort connections, giving board makers the option to offer video cards with a, er, DisplayPort.

The two chips, code-named RV620 and RV635, will replace the current RV610 and RV630 GPUs. The more potent of the two, the RV635, powers the Radeon HD 3650 graphics card. We can't really talk of a Radeon HD 3600 series per se, because the 3650 is initially the only product in this range; the $179 Radeon HD 3850 has already essentially replaced the Radeon HD 2600 XT. That leaves the HD 3650 to supplant the 2600 Pro at a suggested e-tail price range of $79-99.

The Radeon HD 3650. Source: AMD.

AMD estimates the RV635's transistor count at 378 million, which is, surprisingly enough, down from the 390 million transistors in the RV630. I suspect the differences in transistor count come from fairly arcane sources, because the RV635 shares the same basic 3D graphics architecture with the RV630, with three SIMD units that each have eight superscalar execution units. Since those execution units have five ALUs each, AMD says the RV635 has a total of 120 stream processors onboard. Like the RV630, the RV635 can filter eight texels per clock and output four pixels per clock, and it has a 128-bit memory interface.

The Radeon HD 3650 will come in two flavors. The tastier of the two will have GDDR3 memory onboard clocked at 800MHz, and the blander model will use DDR2 memory at 500MHz. Memory sizes will range between the standard-issue 256MB all that way to the goofy 1GB, for those who like lots of RAM on their $79 video cards—you know, as ornamentation. Both flavors will pack a 725MHz core clock, which is up somewhat from the 2600 Pro's 600MHz core. As a result, the 3650 should offer slightly better performance than its predecessor.

AMD rates HD 3650's power consumption at 75W, and as a result, it should be able to get all of its power through the PCIe slot without the need for an auxiliary power plug.

The RV620 shares the same relationship to the GPU it replaces as the RV635. Contained in its 125 million transistors is the same basic 3D architecture as the RV610 that it supplants, fortified with the new features common to this generation of product. That means the RV620 has a total of 40 stream processors, which it pairs with the same 64-bit memory interface as the RV610.

The RV620 will find its way into two different models of Radeon HD. The 3470 replaces the 2400 XT at suggested e-tail pricing between $59 and $65. With an 800MHz core clock and 950MHz of GDDR3 memory, the 3470 should bring a bit of a performance improvement over the Radeon HD 2400 XT. And the 600MHz core and 500MHz DDR2 memory on the Radeon HD 3450 should make it a virtual carbon copy of the 2400 Pro at $49-55. Neither card will require aux power, and the 3450 will be capable of using only passive cooling.

The Radeon HD 3470 (top) and 3450 with DisplayPort (bottom). Source: AMD.

We don't yet have a full suite of Radeon HD 3400 and 3600 cards to review, but AMD did send us an HTPC demo system based on the AMD 690G chipset, the Athlon X2 BE-2400 low-power processor, and the Radeon HD 3450. The system packs a combo Blu-ray/HD-DVD drive, and it's able to play HD movies fluidly without taxing the CPU much, thanks to the 3450's UVD H.264 and VC-1 decode acceleration. The system is also easily quiet enough for any living room. AMD says the machine's component cost was only about $600, and it nicely illustrates how well-suited the GPU is for these applications.

AMD expects all of these new video cards to be available starting today.

Soon, the firm will unveil its new RS780G chipset with integrated graphics, at which point the Radeon HD 3400 series will gain a new capability, as well: hybrid graphics. This CrossFire-like multi-GPU technology will allow the sharing of 3D rendering loads between a chipset-based IGP and a discrete GPU. Hybrid configs will also be able to switch off the unused GPU during normal operation in order to conserve power. AMD is claiming 40 to 80% performance scaling with the combination of a Radeon HD 3450 and an RS780G chipset.

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