Radeon HD 5600 architecture
We covered AMD's flagship architecture in some detail in our Radeon HD 5800 series technology preview, and that article is well worth reading as a precursor to this section of our review if you're new to AMD's latest and greatest. Needless to say, the Radeon HD 5670 takes the basic functionality of this "Cypress" architecture as its cornerstone, from full support to DirectX 11 through to AMD's new Eyefinity technology for multiple monitor support.
Much like its bigger brothers, the Radeon HD 5670 and its "Redwood" codenamed core makes use of a 40 nanometre manufacturing process, with its transistor count of 627 million clocking in at almost half of the 1.04 billion of the Radeon HD 5700 series "Juniper" codenamed parts.
In fact, looking at the Radeon HD 5670 as "half a Radeon HD 5700" is actually pretty much bang on the mark in terms of the card's architecture, with this GPU sporting 400 Stream Processors (against 800 in a "Juniper" part) split into five SIMD units, each housing sixteen cores with five Stream Processors each. Four of these processors are typical units which can handle a single 32-bit floating point instruction per clock cycle, while the fifth Stream Processor in each core is capable of handling special functions (SIN, COS, EXP for example) as well as a 32-bit floating point MAD (MULTIPLY ADD command) per clock. Each group of five Stream Processors is also equipped with its own designated branching unit, as well as general purpose registers to help keep them fed with all of the data they need, while the GPU's Ultra Threaded Despatch processor handles what work is passed to each SIMD before each cores own logic schedules the work for its own particular sub-set of Stream Processors. As per Cypress and Juniper, these Stream Processors also contain a number of minor improvements over AMD's previous generation parts to increase performance while also adding DirectX 11 support.
Texturing capabilities are also halved for "Redwood" over the Radeon HD 5700 series, with the Radeon HD 5670 utilising five texture units which hold four texture processors and texture filtering units for a total of twenty each for the entire GPU, with each unit also holding sixteen texture samplers to give us 80 in total. Again, these units include the DirectX 11 requirements and improved cache bandwidth seen with the Radeon HD 5800 series, while once again this new core is capable of true rotationally invariant anisotropic filtering.
This new core also features eight colour and sixteen Z/stencil render back-ends, or ROPs if you prefer, half that of the Radeon HD 5700 series but with the same set of improvements to each ROP which allows for the use of super-sample anti-aliasing in pre-DirectX 10 titles as well as other performance improvements when handling the likes of Multiple Render Targets. As per the Radeon HD 5700 series, the Radeon HD 5670 finds itself with a 128-bit memory interface - Effectively equivalent to a 256-bit memory bus running GDDR3 in bandwidth terms. Radeon HD 5670 boards will be shipping in variants with both 512MB or 1GB of GDDR5 memory, with the former aiming to hit that $100 price point we mentioned in our introduction.
In terms of clock speeds, a reference Radeon HD 5670 sports a core clock of 775MHz, with memory clocked at 1GHz. The expected maximum power required by this part is 61 Watts, with just 14 Watts typically consumed at idle.