Haswell to Use 4th-Level On-Package Cache to Boost Graphics Performance

Looks like a legit approach to the memory bandwidth issue that all IGP systems have to deal with. Personally, I rather enjoy architectures like Llano which rely on the system memory to (significantly) increase performance. Gives me a reason to push the memory to DDR3-3000+!

We know from history, that Intel carves out variants of chips using a common silicon, by toggling the amount of L3 cache available, number of cores, and even number of iGPU shaders, apart from other natural handles such as clock speeds, voltages, and feature-set. With Haswell, the highest iGPU configuration will make use of a 4th-level cache (L4 cache), that sits on the package, while not being a part of the Haswell silicon. The Haswell silicon will instead be placed on a multi-chip module (MCM) along with a separate die that holds this L4 cache. The L4 cache will serve as a fast memory for the iGPU, while reducing or completely offloading the iGPU's dependency on the system memory as a frame-buffer (UMA).

Such implementations aren't entirely new. IBM has used what's known as the eDRAM (embedded-DRAM), a separate silicon with fast memory and some low-level graphics logic, on some of its its game console processor ASICs. AMD, too, used a technology that's similar in principle, though not in implementation. Certain higher-end 7-series and 8-series graphics chipsets (such as AMD 780G, 790GX, and 890GX) feature what's known as DDR3-Sideport memory, which gives the Radeon IGP access to about 128 MB of fast DDR3 memory, which it can use standalone to offload system memory (UMA), or interleave with it (UMA+Sideport).

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