The process table is a data structure maintained by the operating system to facilitate context switching and scheduling, and other activities discussed later. Each entry in the table, often called a context block, contains information about a process such as process name and state (discussed below), priority (discussed below), registers, and a semaphore it may be waiting on (discussed later). The exact contents of a context block depends on the operating system. For instance, if the OS supports paging, then the context block contains an entry to the page table.
the index of a process table entry associated with a process serves
to identify the process,
and is known as the process id of the process.