File Caching between processes

Question

I'm interested in knowing under windows and linux, does file caching work between processes? if process A reads the whole file, and a new process B wants to read parts of it (or all of it), would it make sense to assume the file is already in memory? or does the caching happen only per file object in each process?

Answer 1

Both Windows and Linux cache file data in system memory, separate from processes. You can't make any assumptions on how much of the file, if any, is still in cache at any given time, however.

At a high level, the operating system maintains a cache of fixed-size pages (normally 4 KB on Linux, 256 KB on Windows). Each page contains part of a file. When your process does a read, the operating system searches the cache for pages with the data you requested. If it can't find all of the data you requested, it reads the required pages into the cache from disk, possibly overwriting other existing pages.