CertiGuide to A+ (Core Hardware)  9  Chapter 0001:  Power Supplies - System Board

Peripheral Component Interconnect (PCI) 1 Why Plug ’n Play is Sometimes Plug and Pray

Prior to 1996, installing an expansion card sometimes felt to the hapless soul charged with doing the install as if they were suddenly thrust into an episode from the Twilight Zone.

The plug and play initiative sought to simplify matters. While many people refer to Plug and Play (PnP) as “Plug and Pray,” a background in the partners needed to make this actually work saves a ton of grief. It is time to look at the quartet that makes PnP work, or not.

There is Plug and Play for real, and what Microsoft may call Plug and Play. Real Plug and Play uses PCI based cards with BIOS. Frequently a Windows installation will query all IRQ’s in an attempt to determine what hardware exists in a computer, and that can include ISA based hardware. In the latter case, sometimes you get lucky. And sometimes you don’t. That is how you get an unknown device.

Expansion hardware. The device you are adding must be Plug and Play capable. Being capable means the device must be able to Identify it when requested and be able to accept resource assignments.

System BIOS. In Plug and Play, BIOS is the conductor of the quartet. Program routines collect information about the devices to determine which device should get what resources. The BIOS communicates this to the Operating System.

Operating System. For an Operating System to use Plug and Play devices it must install software that interfaces between the device and the main Operating System, automatically. These program routines are known as Drivers.

Peripheral Component Interconnect (PCI) 1 Why Plug ’n Play is Sometimes Plug and Pray