Plug and Play

What is Plug and Play (in computer science)?

A design philosophy and set of specifications for PC architectures that enables computer hardware, peripherals, device drivers, and operating systems to be easily reconfigured with minimal user understanding and intervention.

Plug and Play frees users from having to manually configure devices and device drivers when they add or remove peripherals from computer systems. For example, to configure a non–Plug and Play sound card, a user typically has to manually change jumpers or dual inline package (DIP) switches on the sound card itself, a task that is often difficult for the inexperienced user.

With Plug and Play, you simply plug in the device and follow a series of prompts (if any are necessary) to configure the appropriate drivers for your device.

How It Works

A true Plug and Play system consists of the following three elements:

• A Plug and Play operating system such as Microsoft Windows 95, Windows 98, or Windows 2000.
• A Plug and Play system BIOS that supports Advanced Power Management 1.1 (Windows 95) or Advanced Configuration for Power Management (Windows 98), automatic configuration of boot and motherboard devices, hot docking, and other features.
• Plug and Play system buses such as PCI or universal serial bus (USB) and Plug and Play peripheral devices (internal or external) and their associated drivers. Plug and Play peripheral devices include USB, IEEE 1394, SCSI, PCMCIA, and PCI devices. ISA, EISA, and VESA devices are not fully Plug and Play. Other Plug and Play devices include IDE controllers, ECP parallel ports, and video adapters.

If a system does not support all three of these features, it is not truly Plug and Play, although it might have some limited Plug and Play support. In a completely Plug and Play system, these features work together to automatically enumerate (identify) new devices installed on or connected to the system, determine their resource requirements, establish a system configuration that can support these requirements without device conflicts, program the devices as necessary and load their device drivers, and notify the user of the changes to the system’s configuration.

The Windows 95 and Windows 98 components that work together to support Plug and Play include the following:

• Configuration Manager:
  Manages the device configuration process by communicating with the BIOS, motherboard, and peripheral devices.

   

• The hardware tree:
  Contains the current system configuration information. The hardware tree is dynamically constructed by Configuration Manager upon each reboot and uses information in the registry to configure the system’s devices. You can display information stored in the hardware tree by using the Device Manager tab of the System Properties dialog box (double-click the System icon in Control Panel).

   

• Bus and port enumerators:
  Build the hardware tree by enumerating attached devices. Different enumerators are used for each type of system and peripheral bus.

   

• Resource arbitrators:
  Allocate system resources such as interrupt requests (IRQs) and input/output (I/O) ports to devices and resolve conflicts between devices.

   

• Setup and Device Installer:
  Creates the configuration database during initial system setup and can assist in installing non–Plug and Play devices by using the Add New Hardware Wizard.

   

When you add a new hardware device to a Plug and Play system, the Add New Hardware Wizard starts and installs the necessary drivers for the hardware. The wizard selects suitable hardware resources for the device, which might include an IRQ line, I/O address, direct memory access (DMA) channel, and memory range. If the system cannot properly detect the hardware, you can manually run the Add New Hardware Wizard to configure the hardware.