Is accessing data in the heap faster than from the stack?

Question

I know this sounds like a general question and I\'ve seen many similar questions (both here and on the web) but none of them are really like my dilemma.

Say I have t

Answer 1

Your question doesn't really have an answer; it depends on what else you are doing. Generally speaking, most machines use the same "memory" structure over the entire process, so regardless of where (heap, stack or global memory) the variable resides, access time will be identical. On the other hand, most modern machines have a hierarchial memory structure, with a memory pipeline, several levels of cache, main memory, and virtual memory. Depending on what has gone on previously on the processor, the actual access may be to any one of these (regardless of whether it is heap, stack or global), and the access times here vary enormously, from a single clock if the memory is in the right place in the pipeline, to something around 10 milliseconds if the system has to go to virtual memory on disk.

In all cases, the key is locality. If an access is "near" a previous access, you greatly improve the chance of finding it in one of the faster locations: cache, for example. In this regard, putting smaller objects on the stack may be faster, because when you access the arguments of a function, you're access on stack memory (with an Intel 32-bit processor, at least---with better designed processors, arguments are more likely to be in registers). But this will probably not be an issue when an array is involved.