Computer | Hardware Principles

Personal Computer Hardware

The main parts of a personal computer include following:

The CPU:

Arithmetic/Logic Unit (ALU)

Control Unit (CU)

Interface Unit

Memory:

Primary storage

Secondary storage

Peripheral Devices:

A Peripheral is a device attached to a host computer, but not a part of it.

Examples include Input/output devices like:

Monitor

Keyboard

Floppy/CD/DVD drives

Speaker

Printer

Scanner

Light pen

Bus (a bundle of wires)

Channels (separate processor)

CPU: Central Processing Unit

The central processing unit (CPU) is the brain of a computer system.

It carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system.

Below chart depicts all the components of the CPU:

ALU (Arithmetic Logic Unit)

Performs arithmetic and logical operations.

Arithmetic operations include:

Addition, Subtraction, Multiplication and Division

Logic includes:

AND, OR, NOT and Shift

CU (Control Unit)

Performs fetch/execute cycle.

Accesses and retrieves program instructions from the memory and issues commands to the ALU.

Moves data to and from the CPU, registers, and other hardware components.

Registers:

All modern CPUs have an array of registers.

There are at least 32 general purpose registers.

The register can be accessed in one CPU cycle.

The register serves as the source of operands, as the destination of results, and temporarily stores intermediate results.

Memory management unit:

Manages fetching of instructions and data from memory.

I/O Interface

Provides the mechanism for the input/output of data.

Sometimes combined with memory management unit in a single Bus Interface Unit.

Memory

Memory can be classified into two groups.

Primary memory

 Secondary memory

Primary memory:

It is a smaller segment of memory for storing program and data.

The internal memory of a computer system uses electronic semiconductor devices called ROM and RAM.

Secondary memory:

It is used for long term storage of data.

Floppy disk and hard disk are examples.

RAM - Random Access Memory 

RAM is the memory part of a computer that stores information temporarily while the computer is on.

It is this region into which programs are loaded before the CPU processes those informations.

RAM is volatile in nature, which means that the contents are lost once the power supply is switched off.

Two types of RAM are:

Static RAM

Dynamic RAM

Static RAM (SRAM):

SRAM is a type of memory that maintains data in storage as long as it is powered.

Because it is faster and more reliable and expensive than DRAM

Dynamic RAM (DRAM):

DRAM is a type of random-access memory that stores each bit of data in a separate capacitor within an integrated circuit.

ROM - Read Only Memory

It is a Read Only Memory.

Program or data stored in the ROM can only be read; they cannot be altered.

ROM is non-volatile which means that the contents are not changed when the power is switched off.

Types of ROMs:

EPROM

EEPROM

EPROM

An EPROM (rarely EROM), or erasable programmable read only memory, is a type of memory chip that retains its data when its power supply is switched off. In other words, it is non-volatile.

EEPROM

EEPROM stands for Electrically Erasable Programmable Read-Only Memory and is a type of non-volatile memory.

It is used in computers and other electronic devices to store small amounts of data that must be saved when power is removed, e.g., calibration tables or device configuration.

Bus 

Buses are the set of wires that carry special information to or from the CPU.

There are three types of buses:

Address buses: These buses carry address given by the CPU from one unit to another in the computer.

Data buses: These buses carry data from one unit to other; it is a bi-directional bus i.e. the data can be carried in both directions.

Control signal: These buses carry control signal from ALU to memory and from memory to ALU and then to the output unit.