 Common resource handles include file descriptors, network sockets, database connections, process identifiers (PIDs), and job IDs.PIDs and job IDs are explicitly visible integers; while file descriptors and sockets (which are often implemented as a form of file descriptor) are represented as integers, they are typically considered opaque.In traditional implementations, file descriptors are indices into a (per-process) file descriptor table, thence a (system-wide) file table.