4 ms·
Is there a reason why they don't package a couple GB of DRAM in there?
by mantap 7y ago
Is there a reason why they don't package a couple GB of DRAM in there?
- Retric 7y agoActually yes, the cache hit ratio is not linear with cache size so you get diminishing returns. http://www.dataram.com/blog/?p=112 http://www.dataram.com/blog/?p=112. On top of this, once a CPU core is operating at say 80% of the time the maximum possible speed up from more cache is 20%. Further, every layer of cache adds latency and cost as you need to check it before going to main memory. In the 486 and early pentium days External Cache was common, but it’s no longer useful.
- mantap 7y agoI had something more like a swap than a cache in mind. Expose it as additional physical address space and let the OS decide which pages live there vs main memory.
- coretx 7y agoYes. The very same reason why they waited years before they eventually moved the memory controller on to the CPU die. It's expensive m2 real estate and eats a big chunk of the waffer. Furthermore, there is diminishing returns regarding all kinds of cache. Most of the recent performance increases are attributed to the very dangerous practice called branche prediction.