Plug and Play - How a Computer Works (2015)

How a Computer Works (2015)

6. Plug and Play




The Plug and Play standard was introduced to enable devices and peripherals to connect to the computer and work first time. When the computer is switched on. The system boots up.

The BIOS searches for all connected peripherals such as the keyboard, mouse etc.



The BIOS identifies peripherals based on unique codes that are held in the peripherals ROM. After this is completed the BIOS hands over control to Windows. The Windows configuration manager adds device drivers called enumerators to itself.

Different enumerators exist for ports and SCSI. These device drivers act as an interface between Windows and different peripherals.

Windows communicates with each enumerator to establish which peripherals/devices it is going to control and what resources it requires.



Mouse: IRQ 12

Windows places this information into a database in RAM. This information is called the hardware tree. Windows examines the hardware tree for resource arbitration. Windows decides what resources i.e. interrupts (IRQs) to allocate to each peripherals/device.

Programmable Registers


After this is completed the enumerators are allocated resources to their respective peripherals/device. This information is stored in the peripherals/devices programmable registers. The next stage is for Windows to search for the right device driver for each peripheral or device.

The device driver is a small program that contains information for Windows about the peripheral/device. If Windows doesn't find the right device driver it needs, it will prompt you to install it.

Loading Device Drivers


The last stage is for Windows to load all the device drivers it needs and tell each device driver what resources its device is using. The device drivers then initialise their respective peripheral /devices and Windows finishes booting up.