linux cache question

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http://www.linuxquestions.org – Hi all, Ok so I know linux caches all available RAM for faster data access, my question is where is the cache? is it basically the RAM and linux just converts it to cache and calls it cache? and is this process totally different then linux disk cache? I've googled around but I still havent grasp the concept. Maybe I'm thinking too much into it but I really want to understand. Thanks. (HowTos)