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Larger caches is an option for using the extra die area. RAM access times aren't increasing at anywhere near the rate that CPU power has.
by rpledge 14y ago
Larger caches is an option for using the extra die area. RAM access times aren't increasing at anywhere near the rate that CPU power has.
- Joeri 14y agoWhy have caches at all? Couldn't you move the entire RAM on-die.
- sliverstorm 14y agoFirst, SRAM caches are still faster than DRAM. Second, DRAM is made differently from CPUs, and it is difficult to use two different processes on the same silicon. Third, squeezing 4GB of DRAM onto a single CPU die? How?
- JohnBooty 14y agoIt would be prohibitively expensive. Several megabytes of cache already take up about half of the CPU die size. http://techreport.com/review/21987/intel-core-i7-3960x-processor http://techreport.com/review/21987/intel-core-i7-3960x-proce... Think about how much larger a CPU would have to be to include an entire gigabyte of cache, much less multiple gigabytes.
- mzl 14y agoRecently I heard a talk by a guy from Oracle designing Sparc CPUs. IIRC, he said that while they could potentially put bigger caches on their CPUs, for their test-cases it wasn't that much of a benefit above their chosen size. Another interesting note from that talk was that they had spent a large amount of time making an 8 socket architecture with quick-connect paths between all pairs of sockets for memory transport. Unfortunately that was not as important as believed either, since the programs that typically benefit from 8 CPUs normally have good memory properties anyway. Not sure if either data-points are true, but interesting nonetheless.