Starting with RV635, AMD has decided that instead of having separate Pro and XT cards like it did in the Radeon HD 2600 series, it would stick with just one model name in the Radeon HD 3650 series. AMD's Iain McNaughton explained that the company looked at the mainstream segment and asked itself "what can we do that is different and disruptive to our competitors, while offering more value to our customers?"

Despite only offering one model name, there are //still two products that fit under this name -- both share the same engine clock, which is set at 725MHz (slower than the Radeon HD 2600 XT's engine clock), and the same number of stream processors as the Radeon HD 2600 series cards (120 stream processors or 24 five-way superscalar shader units) -- both also feature a 128-bit memory interface.

The number of texture units and raster operators hasn't changed either, meaning there are still just eight texture units and four raster operators (or ROPs). What has changed architecturally now though is that there is support for DirectX 10.1, PCI-Express 2.0 and ATI PowerPlay at a high level... at a much lower level, I've heard (but still waiting for confirmation) that AMD has added double precision support at one quarter speed, but it's not exposed in current 3D graphics APIs.

RV635 also uses fewer transistors---a total of 378 million---than the RV630 chip, which itself featured a pretty massive 390 million of the little blighters. AMD says that it has made some optimisations during the die shrink, which should help to improve performance per clock and efficiency a little bit when it's compared to the ASIC it's replacing at the same clock speed.