The program atop is an interactive monitor to view the load on a Linux system. It shows the occupation of the most critical hardware resources (from a performance point of view) on system level, i.e. cpu, memory, disk and network.
It also shows which processes are responsible for the indicated load with respect to cpu- and memory load on process level. Disk load is shown if per process "storage accounting" is active in the kernel or if the kernel patch `cnt' has been installed. Network load is only shown per process if the kernel patch `cnt' has been installed.