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Definitions

• Physical memory - RAM (Random Access Memory)

• ROM/EPROM - Fixed memory (read at boot time)

• Available memory - Physical memory minus memory used by kernel

• Lockable memory - memory which is used for non swapable/pageable memory. i.e. has to be locked into memory. Controlled by unlockable_mem kernel parameter

• Secondary storage/memory - usually disk, either device swao or file system swap

• swapping - whole process moved in and out of memory

• paging - pages of the process swapped in and out (more efficient than swapping)

• address translation - mapping virtual address space to physical address space

• virtual address space - contains info & pointers to memory the process can reference. Also points to per-process regions (pregions). These point to segments of code, data, etc. used by the process

• vnodes - used by memory management to keep a track of swapped or paged memory

vhand and swapper daemons control paging and swapping.

Notes on memory management

Thrashing - paging and swapping at such a high level, virtually no processing taking place.

File system swap is slower than device swap because it wtites in smaller blocks ( so more writes required) and may not be in contiguous blocks