AMD Radeon Graphics
Cayman - AMD Radeon HD 6900 Series
The Pro and XT designations come from the halcyon days of the Radeon 9500, 9700 and 9800 - the R3xx based chips. Originally, the Pro designation was the top dog, with later lower clocked R300's known as just Radeon 9700, or non-Pro, to contrast with the flagship. The core chip, R300, was followed by R350, which was marketed as the Radeon 9800 series. Initially offered as the Radeon 9800 Pro, it was followed by 9800 XT and SE models, beginning the trend we now see of differing clocks, and shader units, between similarly numbered products. R300 brought one other thing: the Radeon 9500. ATI's Radeon 9500 was the Christmas '02 stop-gap as the RV350 based 9600 was prepared for market. The Radeon 9500 gained fame and fortune when enthusiasts discovered that in some cases it could be 'unlocked' into a full Radeon 9700, giving fantastic price/performance for those daring enough to try.
Unlocking extra computation units is a byproduct of a technique known as 'binning' - a single design is created and manufactured, with those units achieving the desired clock, power and thermal specifications being sold as the premium product the design was created to be. Manufacturing processes are not perfect, however, so its inevitable that some units come through that don't run quite as fast, or quite as cool, or with all computational units and cache intact. Rather than discard these units and write them off as loss, binning allows these products to be sold as lower specification products. AMD, Intel, and Nvidia all do this, ultimately to everyone's benefit - it provides a method to get more products into more price points, cheaper.
Back in the R300 days, CPU cores couldn't be unlocked but multipliers and multi-processor capabilities could via pencil mods. Eventually laser cutting to disable features became the norm, and free performance boosts were gone. Today, unlocking is back again - a mainstream feature in some regards. Several of AMD's processors unlock more cores, including the enthusiast Phenom II X2 565 Black Edition. Successful core unlocks have been performed on all of AMD's processor line-up, from the lowly single-core Sempron, through the Athlon X3s and Phenom II X2/X3, to the OEM-only Thuban based Phenom II X4 960T which becomes a full-on hexacore processor.
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