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.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.