The critical components of a computer are –  the peripherals (including the mouse), –  the input/output (I/O) subsystem (which controls what and how much information comes in and out), and the central processing unit (the brains), as well as human-written programs and memory.
Most input and output devices are much slower than the CPU—so much slower that it would be a terrible waste of the CPU to make it wait for the input devices. For example, compare the speed you can type with the speed the CPU can execute instructions. Even a very fast typist could probably type no more than 10 characters per second, while a modern CPU can execute more than two billion instructions in that same second!
– We have 2 types of schemes for dealing with IN-OUT:
1. Polling:  If the CPU simply waits for the next input character, we call this polled I/O.
2. Interrupts:   Here the CPU works on its given tasks continuously. When an input is available, such as when someone types a key on the keyboard, then the CPU is interrupted from its work to take care of the input data.

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Key Terms:

BIOS = One of the most common uses of Flash memory is for the Basic Input/Output System of your computer, commonly known as the BIOS (pronounced „bye-ose”). On virtually every computer available, the BIOS makes sure all the other chips, hard drives, ports and CPU function together.
The basic input-output system BIOS is the first thing you see when you turn on your computer.BIOS is a (flash-memory) Chip.
BIOS is a type of Firmware used to perform hardware initialization during the booting process.
Firmware: type of software that provides control, monitoring and data manipulation of engineered products and systems. This is held on non-volatile memory devices such as ROM, or flash memory. Changing the firmware of a device may rarely or never be done during its lifetime; some firmware memory devices are permanently installed and cannot be changed after manufacture.