Codenamed RV740, the HD4770 is ATI's latest GPU that's manufactured using TSMC's 40 nanometer fabrication process. While most other chips adopt the 55nm process, AMD have seen fit to test the water with their new chip in the highly competitive budget/performance sector of the graphics card market. A smaller fabrication had benefits that enable the chip to be produced at a smaller cost with the added benefit of consuming less power. Because less power is used, less heat is produced which allows the chip to be clocked higher than before. While I won't go to far into the intricacies of the actual differences between the RV770 and the new RV740, I will say that the chip, at first glance anyway appears to be a slightly scaled down version of the RV770 (used in the 4800 range). There are however a few subtle differences.
The HD4770 has had it's memory interface cut in half from 4x64bit (256bit) to 2x64bit (128bit). This lower interface has however been countered with the use of GDDR5 running at a blistering 800MHz which transfers data at twice the rate as GDDR3. Ultimately the memory bandwidth is therefore not affected too much by the reduction in interfaces. The stock GPU clockspeed is also slightly higher than the HD4850, running at 750MHz which might go some way for making up the lost ground in memory bandwidth and shaders compared to the 4850. To muddy the waters further, the HD4830 has higher memory bandwidth (As it too uses the 256bit interface) but has lower texel filtering and pixel fill rates. Sadly we don't have a HD4830 to include in today's review but on paper, the 4770 has it beat in all categories but memory bandwidth.
The Sapphire version of the 4770 is based on the reference design with stock clocks and stock heat sink. Being a tier one partner of ATI, you can be assured of the quality of produce from Sapphire. Here's what they have to say about their card:
The new SAPPHIRE HD 4770 is the first card in its class to use GDDR5 memory and is based on the first ever GPU built in 40nm process technology. It uses the powerful graphics architectures from the ATI division of AMD, incorporating multi-purpose stream processing units and improved memory management architecture.
24x custom filter anti-aliasing (CFAA) and high performance anisotropic filtering
Dual mode ATI CrossFireX™ multi-GPU support for highly scalable performance
PCI Express® 2.0 support
Dynamic geometry acceleration
Game physics processing capability
ATI Avivo™HD video and display technology
Dynamic power management with ATI PowerPlay™ technology
ATI Stream technology