# top -d 1 -o res -a
last pid: 3627; load averages: 1.14, 1.23, 1.23 up 1307+20:18:3110:24:18
39 processes: 4 running, 35 sleeping
CPU: % user, % nice, % system, % interrupt, % idle
Mem: 831M Active, 2029M Inact, 248M Wired, 99M Cache, 112M Buf, 290M Free
Swap: 8192M Total, 68K Used, 8192M Free
Active: Memory currently being used by a process
Inactive: Memory that has been freed but is still cached since it may be used again. If more Free memory is required, this memory can be cleared and become free. This memory is not cleared before it is needed, because "free memory is wasted memory", it doesn't cost anything to keep the old data around in case it is needed again.
Wired: Memory in use by the Kernel. This memory cannot be swapped out
Cache: Memory being used to cache data, can be freed immediately if required
Buffers: Disk cache
Free: Memory that is completely free and ready to use. Inactive, Cache and Buffers can become free if they are cleaned up.