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Unit 1: Introduction to Hardware and Software
5. Motherboard: Motherboard, also called as System Board, is the most important hardware Notes
component of a microcomputer. Motherboard is so called as all the other boards (printed
circuit boards having chips or other electronic components) of the computer are connected
to this board, hence it is like the mother of all other boards.
Now we will discuss the components of computer hardware in detail.
1.1.1 Central Processing Unit
Central Processing Unit (CPU) is the main component or “brain” of a computer, which performs
all the processing of input data. Its function is to fetch, examine and then execute the instructions
stored in the main memory of a computer. In microcomputers, the CPU is built on a single chip
or Integerated Circuit (IC) and is called as a Microprocessor. The part of a computer (a
microprocessor chip) that does most of the data processing, the CPU and the memory form the
central part of a computer to which the peripherals are attached. The Central Processing Unit
(CPU) is the part of a computer that interprets and carries out the instructions contained in the
software.
The CPU consists of the following distinct parts:
Arithmetic Logic Unit (ALU): The arithmetic and logic unit of CPU is responsible for all
arithmetic operations like addition, subtraction, multiplication and division as well as
logical operations such as less than, equal to and greater than. Actually, all calculations
and comparisons are performed in the arithmetic logic unit.
Control Unit (CU): The control unit is responsible for controlling the transfer of data and
instructions among other units of a computer. It is considered as the “Central Nervous
System” of computer, as it manages and coordinates all the units of the computer. It
obtains the instructions from the memory, interprets them and directs the operation of the
computer. It also performs the physical data transfer between memory and the peripheral
device.
Registers: Registers are small high speed circuits (memory locations) which are used to
store data, instructions and memory addresses (memory location numbers), when
ALU performs arithmetic and logical operations. Registers can store one word of data
(1 word = 2 bytes & 1 byte = 8 bits.) until it is overwritten by another word. Depending on
the processor’s capability, the number and type of registers vary from one CPU to another.
Registers can be divided into six categories viz. General Purpose Registers, Pointer
Registers, Segment Registers, Index Registers, Flags Register and Instruction Pointer
Register, depending upon their functions. The detailed functions of each and every register
is beyond the scope of this book.
Buses: Data is stored as a unit of eight bits (BIT stands for Binary Digit i.e. 0 or 1) in a
register. Each bit is transferred from one register to another by means of a separate wire.
This group of eight wires, which is used as a common way to transfer data between
registers is known as a bus. In general terms, bus is a connection between two components
to transmit signal between them. Bus can be of three major types viz. Data Bus, Control
Bus and Address Bus. The data bus is used to move data, address bus to move address or
memory location and control bus to send control signals between various components of
a computer.
Clock: Clock is another important component of CPU, which measures and allocates a
fixed time slot for processing each and every micro-operation (smallest functional
operation). In simple terms, CPU is allocated one or more clock cycles to complete a
micro-operation. CPU executes the instructions in synchronization with the clock pulse.
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