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Today when I was in computer organization class, teacher talked about something interesting to me. When it comes to talk about Why cache memory works, he said that:
for (i=0; i<M; i++)
for(j=0; j<N; j++)
X[i][j] = X[i][j] + K; //X is double(8 bytes)
it is not good to change the first line with the second. What is your opinions on this? And why it is like that?
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Cached data works by storing data for re-access in a device's memory. The data is stored high up in a computer's memory just below the central processing unit (CPU).
Cache memory is a chip-based computer component that makes retrieving data from the computer's memory more efficient. It acts as a temporary storage area that the computer's processor can retrieve data from easily.
How does cache memory work? Cache memory temporarily stores information, data and programs that are commonly used by the CPU. When data is required, the CPU will automatically turn to cache memory in search of faster data access. This is because server RAM is slower and is further away from the CPU.
There is three types of cache: direct-mapped cache; fully associative cache; N-way-set-associative cache.
There is a very good paper by Ulrich Drepper of Red Hat and glibc fame, What Every Programmer Should Know About Memory. One section discussed caches in great detail. For example, there are cache effects in SMP systems where CPUs can end up thrashing ownership of a modified cache line back and forth, greatly harming performance.
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