How to make it cheapHow to make it cheap
As is the norm these days, AMD/NVIDIA will introduce a range-topping architecture and then pare it down to meet certain price-points. Reducing the constituents that make largely define performance - shaders, memory bandwidth, ROPs, et al - means that a small, cheaper-to-produce die-size is used - leading to, well, cheaper GPUs and boards. The trick, we suppose, is in successfully balancing the mutually exclusive characteristics of performance vs. cost.
Radeon HD 4850 and HD 4870 (£110 and £170, respectively) were launched as mid-sized dies, and two were coupled to form the el-speedy champion that is Radeon HD 4870 X2 (£330). Later, the basic design was chopped down to form the Radeon HD 4670 retailing for around £55 in GDDR3 form. This outlay, however, may still be too great for some to bear, and that is why a cheaper, slower solution is required.
The top-to-bottom range also means that the runt of the litter is imbued wit the same DX10.1 API support as its also-55nm-based brethren, although the speed at which the card will be able to process the good-looking effects is questionable.
This is Radeon HD 4550 when viewed in architectural block-diagram form. Now take a look at the Radeon HD 4670 and Radeon HD 4850/4870's and you'll see that, as expected, it's rather bare.
Thinking of it in comparison to the £55 HD 4670, the stream processors are down from 320 to 80, texture units from 32 to 8, ROPs from 8 to 4, and memory bandwidth from a 128-bit bus to 64-bit - massive chops all-round.
The quoted figures don't sound compelling but they're, in some cases, almost 2x what AMD was offering with the previous-generation (even cheaper) budget offering - Radeon HD 3450/70.
A brain the size of Stephen Hawking's is not required to intimate that HD 4550 will process at significantly less than half the speed of the HD 4670: the basic building blocks of gaming performance aren't there. Die-space is saved, of course, with 4550 weighing in at 73mm² compared to the 4670's 146mm²
That, however, only tells one part of the story. Look to the right-hand side of each of the block diagrams and you'll see they're the same. This is where the multimedia-related functionality is, for want of a better word, 'stored'.