As you would expect, these cards are based on similar architectures to the HD 2900 XT, just with less of everything. Where the HD 2900 XT has 320 stream processors, the 2600 has 120 and the 2400 a mere 40. The core of the 2900 is made up of 700 million transistors whereas the 2600 and 2400 contain only 390 million and 180 million transistors, respectively. These new cores are also built using a 65nm process, as opposed to the 80nm process used for the 2900 XT, which means the chips are relatively smaller and more efficient. Not only does enable the cards to kick out less heat and be made smaller, they can actually be clocked higher than the 2900 XT.
The 2600 XT core and memory run at 800MHz and 1,100MHz, respectively, while the Pro version is throttled to 600MHz and 400MHz. The 2400 XT runs with a 700MHz/700MHz (core/memory) configuration while the 2400 Pro is cut back to 525MHz/400MHz. Compare this to the 742MHz core speed that the 2900 XT could manage and you can see how much of an impact the difference in manufacturing techniques makes.
Both the 2600 and 2400 cards will have 256MB of memory but the 2600 will talk to it across a 128-bit wide interface whereas the 2400 is restricted to a 64-bit width. These are relatively low figures when compared to the massive 512-bit interface used on the 2900 XT. However, the similarly priced nVidia cards also have their memory bandwidth restricted to similar figures. Fundamentally, the lower bandwidth is only an issue if you're running at high resolutions (above 1,600 x 1,200), which is something you shouldn't hope to be doing on cards of this calibre.
These lower cards also retain the tesselation engine that was present on the HD 2900 XT, though there is still no sign that this will be utilised within the near future.
Both the 2600 and 2400 come with ATI's latest video processing engine, dubbed Universal Video Decoder (UVD). By accelerating the CPU intensive task of decoding high-definition video, UVD frees up the CPU to do other tasks like recording a TV programme or running an anti-virus scanner. UVD doesnâ€™t just accelerate the decoding of HD content though, it also applies filtering and post processing techniques to improve the quality of the video. All in all, it makes watching the latest HD-DVD or Blu-ray movies as easy and pleasurable as possible.
UVD isn't unique, though, and nVidia also boasts some very capable video enhancements on its latest cards. However, ATI trumps nVidia on a couple of fronts with its version.
The first, and perhaps most important, difference is that all ATI's cards are fully HDCP compliant. This is in contrast to nVidia who have made HDCP compliance optional, making the process of choosing and buying one of their cards all the more complicated. HDCP is essential for playing back protected HD content using your computer. Without it the resolution of the video is forcibly lowered, reducing detail and quality. All commercial HD-DVD and Blu-ray discs are protected so if you plan to use a Home Theatre PC (HTPC) as your HD movie player it is going to need HDCP.
The second thing that ATI have done to make our lives easier is integrate an audio controller onto its cards. This enables the card to suck up the audio signal from the PCIe bus and squirt it out the DVI ports along with the video signal (this works in conjunction with a normal sound card, not instead of). When combined with the included DVI to HDMI adapter you have a one cable solution for connecting your computer to your TV, which again makes it perfect for use in a HTPC. This beats nVidia's solution that requires a cable to be run from your sound card or motherboard (if you have on-board sound) to the graphics card.
So that's the basics of ATI's new range of cards now letâ€™s take a look at the boards themselves.