Sorry that I do not make myself understood. I know what cache is. :-)
CPU L2/L3 is acting as a cache between CPU and RAM, RAM is acting as cache between disk and L2/L3.
My question is, physical memory stores information of part of (or all) the virtual memory of a process (shared library by a process, private code by a process, private data of a process, shared data of a process), System cache has a different name, and should stores something different, what are the specific information which is stored in System cache compared with the above mentioned normal physical memory.