3 ms·

No, a cell of L1 cache is exactly as expensive as a cell of L3 cache (ignoring weird stuff like eDRAM). Now, SRAM is these days made with 6 or 8 transistors wh

No, a cell of L1 cache is exactly as expensive as a cell of L3 cache (ignoring weird stuff like eDRAM). Now, SRAM is these days made with 6 or 8 transistors while the the DRAM you use in your main memory only takes 1 transistor per cell. Also your DRAM is built with a different sort of silicon process so it cheaper on a transistor to transistor basis. But generally the dollar cost is the same for memory in any given location.

emcq 10y ago
Given a fixed area which fits a fixed number of transistors at the same cost, you allocate some portion of those transistors to compute and memory cells. If you want to maintain your number of memory cells without decreasing the number of compute transistors, you need to grow your area which increases costs. That can be a very expensive thing here. Additionally engineer time around layout and architectural costs are different for those different placements and cache requirements, so the cost is not uniform, but amortized it is not as significant as things like chip area.
- Symmetry 10y ago
  Changing a chip from having 8kB of L1 Dcache to 16kB might be far more expensive in design terms than making a similar change in L3 cache but from a blank slate would either be more expensive to design in the first place? When I look at the layout of a late model x86 the regular structures of the caches stand out in the die photos among the irregular hand-tuned logic. Yes, there are follow on effects on the layout from changes in cache size but I don't see any reason a priori to say whether increasing the L1 size will tend to make designing the rest of the core logic harder or easier. So I still don't see any reason to back off from saying that a cell of L1 costs as much as a cell of L3, modulo concerns about keeping the cache size a power of 2.

3 ms·

No, a cell of L1 cache is exactly as expensive as a cell of L3 cache (ignoring weird stuff like eDRAM). Now, SRAM is these days made with 6 or 8 transistors wh

by Symmetry 10y ago

emcq 10y ago
Given a fixed area which fits a fixed number of transistors at the same cost, you allocate some portion of those transistors to compute and memory cells. If you want to maintain your number of memory cells without decreasing the number of compute transistors, you need to grow your area which increases costs. That can be a very expensive thing here. Additionally engineer time around layout and architectural costs are different for those different placements and cache requirements, so the cost is not uniform, but amortized it is not as significant as things like chip area.
- Symmetry 10y ago
  Changing a chip from having 8kB of L1 Dcache to 16kB might be far more expensive in design terms than making a similar change in L3 cache but from a blank slate would either be more expensive to design in the first place? When I look at the layout of a late model x86 the regular structures of the caches stand out in the die photos among the irregular hand-tuned logic. Yes, there are follow on effects on the layout from changes in cache size but I don't see any reason a priori to say whether increasing the L1 size will tend to make designing the rest of the core logic harder or easier. So I still don't see any reason to back off from saying that a cell of L1 costs as much as a cell of L3, modulo concerns about keeping the cache size a power of 2.