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Are you sure you're not thinking of raw read() / write() (the operating systems calls) rather than fread() and fwrite() (the C standard library functions)? fread and fwrite already have a cache, so repeated calls won't make lots of OS calls.

Or, at least, they shouldn't! Clearly OP's implementation was a counterexample (it made lots of OS calls just for a single fread call).

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Unfortunately not all of them. It depends on the device you are using, and the storage device, and the kernel, and the CRT you are using. The process I was using went from like 20-30 seconds to run to less than a second once I put a cache in front of it. Current implementations may have that cache. I would look first and see what they are doing. At the time I was working with about 6 different CRT's of varying age and quality. Some systems you can turn it on and off per device, or global, or per call depending on flags passed in. Really it comes down to reading the docs (probably right), and testing it out (empirical evnidence). That project I learned to not trust the c runtime libraries. But to verify what they are doing and re-read the docs and make sure I am even using the thing correctly vs what is written in the code and my assumptions.

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