Mem: physical memory usage
swap: swap partitioning
+ buffers / cache :( available) amount of memory, i.e., free + buffers + cached
number memory -buffers / cache :( used), i.e.-buffers-cached Used
Total: the total size of physical memory currently 980M
used: physical memory size has been used in the current 852M
as free: free physical memory size of the current 127M
shared: multiple processes to share physical memory size
buffers buffer: buffer memory current number 73M
cached Page: the current number of cache memory 218M
Available memory is calculated as:
available memory = free + buffers + cached
i.e. 127MB + 73MB + 218MB = 420MB