Page 17 - Computer Science V2.0 Class 11

result of the computation. For storing and accessing the information mentioned above, the CPU requires high-speed
temporary storage units, called registers. Several registers are also equipped with circuitry for performing elementary
operations like addition and subtraction. However, as the registers are much more expensive than the main memory,
the CPU has only a limited number of them.
Arithmetic Logic Unit (ALU): The Arithmetic Logic Unit (ALU) of the CPU performs all arithmetic (+,-,*,/) and logical
(>,<,>=,<=,<>) operations. While the result of an arithmetic operation is a numeric value, the result of a logical operation
(such as 7<8) is either True or False. The values True and False are called Boolean values in honour of George
Boole, who developed an algebra (again named, Boolean algebra, in his honour) that constitutes the basis of all
computer computations. The data for executing an instruction may already be available in the registers or fetched in
the ALU registers from the computer's memory. The result of a computation is often stored in the computer's memory.
Control Unit (CU): The Control Unit (CU) controls the execution of instructions and the flow of data amongst the
components of a computer, i.e., from input devices to memory, memory to ALU and vice versa, and from memory
to output devices. It sends instructions in the form of control signals to ALU to perform the required arithmetic and/
or logical operations.

Central Processing
Unit

Cache
Main Memory
Memory Input/Output
Devices
ALU

Backing or
Auxiliary Key
Storage Control Unit Data
Control

Fig 1.3: Components of a CPU

A microprocessor is a CPU on a single chip. It is built as an integrated circuit (IC), possibly comprising millions
of circuits. A microcontroller is a small computing device consisting of a CPU, RAM, ROM and other peripherals
embedded in some other device such as an air conditioner, a washing machine, or an automobile. A microcontroller
typically performs a dedicated task without human intervention.

1.2 Input Devices

An input device takes input from a user in the form of data or instructions. Some of the commonly used input devices
are described below (see Fig 1.4):

1.2.1 Keyboard

A keyboard is the most commonly used input device. Most of the keys have a symbol printed on them. When a user
presses a key, it is conveyed to the system. Keys are often used in a combination, for example, when the key with the
letter A printed on it is pressed, the system gets the character a. However, when the key shift is pressed, followed
by the key A, while still holding the key shift pressed, the system gets the character A. A keyboard has several special
keys, each having designated purpose, such as function, direction, and caps lock keys.

Computer Fundamentals 3