Microsoft worked with several hardware manufacturers to define a new Plug and Play BIOS specification, which defines the interactions among a Plug and Play BIOS, Plug and Play devices, and option ROMs (sometimes called adapter ROMs). The Plug and Play BIOS enables and configures Plug and Play boot devices. The Plug and Play BIOS also passes configuration information to Configuration Manager in Windows 95 for configuring the remaining adapters and devices.
For legacy computers that do not have Plug and Play BIOS, the BIOS enables all devices on the ISA bus. A Plug and Play ISA card that has an option ROM must start up when the computer is turned on with the option ROM enabled.
A Plug and Play BIOS accesses nonvolatile RAM to determine which Plug and Play ISA cards should be enabled, where their option ROMs should be mapped, and what I/O, DMA, and other assignments are to be given to the cards.
The BIOS then programs the Plug and Play cards before the power-on self-test (POST). All cards that do not have configurations stored in the BIOS are disabled completely, reducing the chance of a conflict.
The Plug and Play BIOS also configures all devices on the motherboard. Some devices might have been disabled or assigned to different I/O addresses, IRQ settings, and so on, by Configuration Manager.