Components of computer hardware

Components of Computer Hardware
The computer system hardware comprises of three main components —
1. Input/Output (I/O) Unit,
2. Central Processing Unit (CPU), and
3. Memory Unit.
The I/O unit consists of the input unit and the output unit. CPU performs calculations
and processing on the input data, to generate the output. The memory unit is used to
store the data, the instructions and the output information. Figure 1.14 illustrates the
typical interaction among the different components of the computer.
Figure 1.14 The computer system interaction
Input/Output Unit The user interacts with the computer via the I/O unit. The Input
unit accepts data from the user and the Output unit provides the processed data i.e.
the information to the user. The Input unit converts the data that it accepts from the
user, into a form that is understandable by the computer. Similarly, the Output unit
provides the output in a form that is understandable by the user. The input is provided
to the computer using input devices like keyboard, trackball and mouse. Some of the
commonly used output devices are monitor and printer.
Central Processing Unit CPU controls, coordinates and supervises the operations of
the computer. It is responsible for processing of the input data. CPU consists of
Arithmetic Logic Unit (ALU) and Control Unit (CU).
 ALU performs all the arithmetic and logic operations on the input data.
 CU controls the overall operations of the computer i.e. it checks the sequence
of execution of instructions, and, controls and coordinates the overall
functioning of the units of computer.
Additionally, CPU also has a set of registers for temporary storage of data,
instructions, addresses and intermediate results of calculation.

Memory Unit Memory unit stores the data, instructions, intermediate results and
output, temporarily, during the processing of data. This memory is also called the
main memory or primary memory of the computer. The input data that is to be
processed is brought into the main memory before processing. The instructions
required for processing of data and any intermediate results are also stored in the
main memory. The output is stored in memory before being transferred to the output
device. CPU can work with the information stored in the main memory. Another
kind of storage unit is also referred to as the secondary memory of the computer. The
data, the programs and the output are stored permanently in the storage unit of the
computer. Magnetic disks, optical disks and magnetic tapes are examples of
secondary memory.
CENTRAL PROCESSING UNIT
Central Processing Unit (CPU) or the processor is also often called the brain of
computer. CPU (Figure 2.1) consists of Arithmetic Logic Unit (ALU) and Control
Unit (CU). In addition, CPU also has a set of registers which are temporary storage
areas for holding data, and instructions.
CPU executes the stored program instructions, i.e. instructions and data are stored
in memory before execution. CPU also acts as an administrator and is responsible
for supervising operations of other parts of the computer.
The CPU is fabricated as a single Integrated Circuit (IC) chip, and is also known as
the microprocessor. The microprocessor is plugged into the motherboard of the
computer (Motherboard is a circuit board that has electronic circuit etched on it and
connects the microprocessor with the other hardware components).
Figure 2.1 CPU

Arithmetic Logic Unit
 ALU consists of two units—arithmetic unit and logic unit.
 The arithmetic unit performs arithmetic operations on the data that is made
available to it. Some of the arithmetic operations supported by the arithmetic
unit are—addition, subtraction, multiplication and division.
 The logic unit of ALU is responsible for performing logic operations. Logic
unit performs comparisons of numbers, letters and special characters. Logic
operations include testing for greater than, less than or equal to condition.
ALU performs arithmetic and logic operations, and uses registers to hold the data
that is being processed.
Registers
 Registers are high-speed storage areas within the CPU, but have the least
storage capacity.
 Registers store data, instructions, addresses and intermediate results of
processing. Registers are often referred to as the CPU’s working memory.
 The data and instructions that require processing must be brought in the
registers of CPU before they can be processed. For example, if two numbers
are to be added, both numbers are brought in the registers, added and the result
is also placed in a register.
 Registers are used for different purposes, with each register serving a specific
purpose. Some of the important registers in CPU (Figure 2.2) are as follows—
 Accumulator (ACC) stores the result of arithmetic and logic operations.
 Instruction Register (IR) contains the current instruction most recently
fetched.
 Program Counter (PC) contains the address of next instruction to be
processed.
 Memory Address Register (MAR) contains the address of next location
in the memory to be accessed.
 Memory Buffer Register (MBR) temporarily stores data from memory
or the data to be sent to memory.
 Data Register (DR) stores the operands and any other data.
 The number of registers and the size of each (number of bits) register in a
CPU helps to determine the power and the speed of a CPU.
 The overall number of registers can vary from about ten to many hundreds,
depending on the type and complexity of the processor.

Figure 2.2 CPU registers
 The size of register, also called word size, indicates the amount of data with
which the computer can work at any given time. The bigger the size, the more
quickly it can process data. The size of a register may be 8, 16, 32 or 64 bits.
For example, a 32–bit CPU is one in which each register is 32 bits wide and
its CPU can manipulate 32 bits of data at a time. Nowadays, PCs have 32–bit
or 64–bit registers.
 32-bit processor and 64-bit processor are the terms used to refer to the size of
the registers. Other factors remaining the same, a 64-bit processor can process
the data twice as fast as one with 32-bit processor.
Control Unit
 The control unit of a computer does not do any actual processing of data. It
organizes the processing of data and instructions. It acts as a supervisor and,
controls and coordinates the activity of the other units of computer.
 CU coordinates the input and output devices of a computer. It directs the
computer to carry out stored program instructions by communicating with the
ALU and the registers.
 CU tells when to fetch the data and instructions, what to do, where to store the
results, the sequencing of events during processing etc.
 CU also holds the CPU’s Instruction Set, which is a list of all operations that
the CPU can perform.
The function of a (CU) can be considered synonymous with that of a conductor of
an orchestra. The conductor in an orchestra does not perform any work by itself but
manages the orchestra and ensures that the members of orchestra work in proper
coordination.

Components of computer hardware

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Components of computer hardware