MojoKid writes: When Intel debuted Haswell this year, it launched its first mobile processor with a massive 128MB L4 cache. Dubbed "Crystal Well," this on-package (not on-die) pool of memory wasn't just a graphics frame buffer, but a giant pool of RAM for the entire core to utilize. The performance impact from doing so is significant, though the Haswell processors that utilize the L4 cache don't appear to account for very much of Intel's total CPU volume. Right now, the L4 cache pool is only available on mobile parts, but that could change next year. Apparently Broadwell-K will change that. The 14nm desktop chips aren't due until the tail end of next year but we should see a desktop refresh in the spring with a second-generation Haswell part. Still, it's a sign that Intel intends to integrate the large L4 as standard on a wider range of parts. Using EDRAM instead of SRAM allows Intel's architecture to dedicate just one transistor per cell instead of the 6T configurations commonly used for L1 or L2 cache. That means the memory isn't quite as fast but it saves an enormous amount of die space. At 1.6GHz, L4 latencies are 50-60ns which is significantly higher than the L3 but just half the speed of main memory.
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