FreeBSD includes several programs for examining system performance. Among these are vmstat(8), iostat(8), and systat(1). We'll discuss vmstat because I find it most helpful; iostat(8) is similar to vmstat(8), and systat(1) provides the same information in an ASCII graphical format.
vmstat(8) shows the current virtual memory statistics. While its output takes getting used to, vmstat(8) is very good at showing large amounts of data in a small space. Type
vmstat at the command prompt and follow along.
vmstatprocs memory page disks faults cpu r b w avm fre flt re pi po fr sr ad0 in sy cs us sy id 3 0 0 580416 1388912 234 11 7 0 209 0 0 171 5796 3816 3 10 87
vmstat divides its display into six sections: ...