The r15s, r1m and r15m load indices are the 15-second, 1-minute and 15-minute average CPU run queue lengths. This is the average number of processes ready to use the CPU during the given interval.
On Linux/UNIX, run queue length indices are not necessarily the same as the load averages printed by the uptime(1) command; uptime load averages on some platforms also include processes that are in short-term wait states (such as paging or disk I/O).
On multiprocessor systems, more than one process can execute at a time. The run queue value on multiprocessor systems is scaled to make the CPU load of uniprocessors and multiprocessors comparable. The scaled value is called the effective run queue length.
The CPU run queue length is adjusted based on the relative speeds of the processors (the CPU factor). The normalized run queue length is adjusted for both number of processors and CPU speed. The host with the lowest normalized run queue length runs a CPU-intensive job the fastest.
The pg index gives the virtual memory paging rate in pages per second. This index is closely tied to the amount of available RAM memory and the total size of the processes running on a host; if there is not enough RAM to satisfy all processes, the paging rate is high. Paging rate is a good measure of how a machine responds to interactive use; a machine that is paging heavily feels very slow.
On Linux/UNIX, the it index is the interactive idle time of the host, in minutes. Idle time is measured from the last input or output on a directly attached terminal or a network pseudo-terminal supporting a login session. This does not include activity directly through the X server such as CAD applications or emacs windows, except on Solaris and HP-UX systems.
On Windows, the it index is based on the time a screen saver has been active on a particular host.
The mem index is an estimate of the real memory currently available to user processes. This represents the approximate size of the largest process that could be started on a host without causing the host to start paging.
Free memory is calculated as a sum of physical free memory, cached memory, buffered memory and an adjustment value.