The term Legacy Plug and Play, also shortened to Legacy PnP, describes a series of specifications and Microsoft Windows features geared towards operating system configuration of devices and IDs are assigned by UEFI Forum. The standards were primarily aimed at the IBM PC standard bus, later dubbed Industry Standard Architecture (ISA). Related specifications are also defined for the common external or specialist buses commonly attached via ISA at the time of development, including RS-232 and parallel port devices. ACPI is the successor to Legacy Plug and Play.