Disk Scheduling is done by operating systems to schedule I/O requests for the disk. Disk Scheduling is also known as I/O Scheduling. The main goal of Disk Scheduling is to reduce the Seek Time and it is done by applying various Disk Scheduling Algorithms.

In an operating system that uses paging for memory management, a page replacement algorithm is needed to decide which page needs to be replaced when new page comes in. The process of replacement is sometimes called swap out or write to disk.

CPU Scheduling is a process of determining which process will own CPU for execution while another process is on hold. The main task of CPU scheduling is to make sure that whenever the CPU remains idle, the OS at least select one of the processes available in the ready queue for execution.