Memory RAM usage

bearophile bearophileHUGS at
Wed Dec 30 16:49:00 PST 2009

Today PCs have lot of RAM, so reducing the memory used by a program may seem not so important, but practice shows that reducing the memory used by a program reduces the cache traffic and increases cache coherence, so the code runs faster (I have recently seen a 13X speedup in a not synthetic program just modifying how memory is used and reducing memory usage, keeping the same algorithm. I can show you an URL if you want). So reducing memory (and improving cache usage patterns) is very important for D programs that want to run fast.

Do you know how can Free Pascal use so little RAM? Here in this nbody benchmark (a simple N body gravitational simulation) it seems to use less than half of the memory used by C, yet the C code is tight and clean enough, and both use 64 bit floating point numbers:
In other benchmarks memory usage of Free Pascal is not dramatically lower, but it's usually near the top of lower memory usage in all Shootout benchmarks.


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