ATI Radeon 4800 series

Introduction
ATI Technologies, now part of AMD, is one of the big three players with respect to manufacturing GPUs (graphics processing units). GPUs can either be integrated (on to a chipset) or discrete, which usually entails more higher performance and more power. GPUs are required to provide video output (2D) and, potentially, gaming (3D) performance for both desktop and mobile (notebook) environments.

Recent research by Jon Peddie suggests that Intel has around 50 per cent of the market - focussing on integrated GPUs in volume-selling PCs and notebooks - NVIDIA commands around 27 per cent and ATI some 20 per cent, with the bulk of the latter two's income made up from sales of discrete cards. All other players account for the remaining three per cent, by the way.

ATI has been focussing on bringing new, ever-faster architectures to market on a yearly cycle, and the current cream of the crop is the Radeon HD 4800 family, released in June 2008.

Radeon HD 4850/4870/X2
The usual method of in creating next-generation graphics architectures requires that a top-heavy approach be used, that is, an expensive, transistor-heavy, range-topping model is introduced and is then followed, later, by cheaper derivatives that use the same underlying core technology but are 'cheapened' by lopping off parts of the somewhat modular architecture. NVIDIA has done this with GeForce 8- 9- and GTX 260-series and ATI, too, has followed such an approach in the past.

The introduction of the Radeon HD 4850/4870 GPUs took a different approach, whereby ATI's engineers focussed on a mid-sized die and packed as much performance and feature goodness into it, rather than opt for a larger die and derivate down. What that meant at launch was that the HD 4800-series family wasn't as fast as NVIDIA's GeForce GTX 280 say, but with a smaller die made possible by a smaller manufacturing process - 55nm vs. 65nm - ATI's been able to maximise efficiency for mid-priced GPUs - going after the mass-market, if you will.

The Radeon HD 4850 packs in an impressive feature-set for a card, made available by partners, that costs around £120 right now. Pragmatically, the GPU uses 800 cores that produce, theoretically, around 1TFLOPS of compute performance when clocked in at a default 625MHz, which is around 50 per cent higher than price-equivalent NVIDIA GPUs. The GPU connects via a 256-bit memory interface to either 512MB (usual) or 1024MB of card-mounted memory that's run at an effective 2GHz, so around 64GB/s of potential bandwidth.

Real-world performance is such that the DX10.1-compliant GPU is able to render the latest games - Call of Duty 4, Race Driver: GRID, Company of Heroes, etc. - at a 1,280x1,024-resolution, with high degrees of image-quality enhancement, at average frame-rates of >30fps.

Whilst good with respect to gaming power, Radeon HD 4850 also features a robust multimedia feature-set, including on-board HDMI 7.1-channel passthrough and a UVD2 engine that helps upscale DVD resolution to 1080p and provides GPU-based assistance for playing back computationally-expensive high-definition content - Blu-ray, for example.

HD 4850 currently competes favourably against NVIDIA's GeForce 9800+ and 9800 GTX+ products, providing, on balance, a touch more performance than either.

Radeon HD 4870, introduced at the same time, is based on the same architecture but adds in higher frequencies for the core - 750MHz vs. 625MHz - leading to more basic compute power - 1.2TFLOPS vs. 1TFLOPS - and a much-faster memory interface by using GDDR5 RAM instead of GDDR3.

HD 4870 is the first graphics card to be endowed with super-fast GDDR5, operating at an effective 3.6GHz, which provides around 115GB/s of bandwidth via the 256-bit bus. Just like the HD 4850, the card is available in 512MB (£175) and 1GB (£210) frame-buffer sizes

Benchmarks show that the Radeon HD 4870 is around 30 per cent faster than the HD 4850 when the resolution and image-quality is turned up, and the GPU competes evenly against NVIDIA's GeForce GTX 260 and 280 products.

Analysing further, ATI knew that it would be difficult to usurp NVIDIA's 1.4bn transistor GeForce GTX 280 as the performance-leader GPU and thus engineered the Radeon HD 4870 X2 - a one-card solution that amalgamates two Radeon HD 4870 1GB GPUs on to one PCB and uses ATI's CrossFireX technology as the conduit for inter-GPU communication. The sheer power of the twin-GPU card is such that it bests NVIDIA's single-GPU GeForce GTX 280 when run at ultra-high resolutions.

Radeon HD 4830
ATI has recently extended the Radeon HD 4800 family by introducing the sub-£100 HD 4830 - a GPU that provides around 75 per cent of the performance of the HD 4850. Analysis shows that the slower-clocked card to comprise of GPUs that don't quite make the HD 4850 grade.

It, however, carries the same bountiful multimedia feature-set as the more-expensive duo and provides direct competition for NVIDIA's GeForce 9800 GT, which is also priced at around £90-£100.

More than a GPU?
Both NVIDIA and ATI have been at pains to disseminate that their GPUs, which are broadly similar in architecture, are more than just facilitators of high-octane gaming thrills and spills. The massively parallel architectures boast incredible computer power, which, on even mid-range parts, can be 5x that pushed out by the latest quad-core CPUs from Intel and AMD.

Workloads that can be split into chunks and processed in parallel benefit greatly from being run on a GPU, assuming the correct software infrastructure is in place. Media-encoding is often cited as an example of how GPUs can be set to process far more quickly than CPUs, and both NVIDIA and ATI (and their partners) are slowly releasing GPU-optimised software that take advantage of the power on tap.

NVIDIA is ahead in this respect, having rolled out media encoders and plug-ins for professional software - Adobe CS4 springing to mind - but ATI will launch a high-definition, on-GPU decoder in December 2008.

Summary
ATI's Radeon HD 4800-series of GPUs target the £90-£350 discrete graphics-card market and compete well against their NVIDIA counterparts. High on performance, with respect to both 3D and multimedia, they make compelling reasons for purchase as both gaming and burgeoning GPGPU solutions.