What Does Plug and Play Mean?
Plug and Play (PnP) is a technology that allows the operating system to detect and configure internal and external peripherals as well as most adapters. It has the ability to find and configure hardware components without having to reset DIP switches and jumpers. PnP also refers to hot swapping, or hot plugging, structures such as Firewire or USB sticks and other devices.
When booting a PC, PnP identifies the attached peripheral devices and regulates the proper internal settings by configuring the direct memory access (DMA), interrupt requests (IRQ) and input/output (I/O) addresses.
Techopedia Explains Plug and Play
Most modern devices have a PnP compatible BIOS. Newer systems such as Firewire and USB are intentionally constructed to support changes in configuration settings.
For PnP to function it requires support from software and hardware. The hardware uses an ID code, allowing it to be identified by the software. The ID code consists of either a four-bit code or larger bits containing names and serial numbers. Before the industry standard architecture (ISA) was introduced, PnP did not have an ID code and was not very dependable. IRQ lines and I/O addresses would be often be set incorrectly, causing malfunction. When the peripheral component interconnect bus was introduced, PnP was finally became dependable.