Introduction to PC

A personal computer (PC) is a computer that can perform all of its input processing, output and storage activities by itself, i.e. it contains at least one input device, one output device, one storage device, memory and a processor. The processor called a microprocessor, is a central processing unit (CPU) on a single chip and is the basic building block of a PČ.
Two popular series of PCs are the IBM PC and the Apple Macintosh. These two types of computers have different processors and different operating systems. The PC and compatibles use the Windows operating system. Today the terms PC and compatibles are used to refer to any personal computer that is based on specifications of the original IBM PC computer. Companies such as Gateway, Compaq, Dell and Toshiba all sell PC compatible computers.
A computer is a composition of various parts, which are housed together in a box. A first glance, you will find a monitor, keyboard, mouse and a box. But when you will observe the box, you will find that the major organs of a computer are housed inside that box. That box is called as a system unit.

The system unit

The system unit is a box like case that houses the electronic components of the computer that are used to process data. The system unit is made of metal or plastic and is designed to protect the electronic components from damage. On a desktop personal computer, the electronic components and most storage devices reside inside the system unit. Other devices, such as keyboard, mouse; monitor and printer normally are located outside the system unit. A laptop computer houses almost all of its electronic components in the system, unit.

Inside the system unit

The motherboard

It is the main printed circuit board, which contains the sockets that accepts additional boards. In a personal computer, the motherboard contains the bus, CPU and coprocessor sockets, memory sockets, keyboard controller and supporting chips.
Chips that control the video display, serial and parallel ports, mouse and disk drives may or may not be present on the motherboard If not, they are independent controllers that are plugged into an expansion slot on the motherboard.

The central processing unit

The CPU or central processing unit interprets and carries out the basic instructions that operate a computer, The CPU, also referred to as a processor, significantly imparts overall computing power and manages most of a computer's operations. That is, most of the devices connected to the computer communicate with the CPU in order to carry out a task. The CPU contains the control unit and the arithmetic/logic unit. These two components work together to perform the processing operations.
On larger computers, such as mainframes and super computers, the various functions performed by the CPU are spread across many separate chips and sometimes multiple circuit boards. On a personal computer, the CPU usually is contained on a single chip and sometimes is called a microprocessor.
In addition to the control unit and the arithmetic /logic unit, a microprocessor usually contains the registers and system clock. Each of these microprocessor components in the following sections.

The control unit

As you know, a program or set of instructions must be stored in memory for a computer to process data. The CPU uses its control unit to execute these instructions. The control unit, one component of CPU, directs and co-ordinates most of the operations in the computer. The control unit has a role much like a traffic cop: it interprets each instruction issued by a program and then initiates the appropriate action to carry out the instruction. For every instruction, the control unit repeats a set of 4 basic operations: 1) fetching an instruction 2) decoding the instruction 3) executing the instruction 4) storing the instruction. Together these 4 instructions comprise a machine cycle.

The arithmetic /logic unit

The arithmetic/logic unit (ALU), another component of the CPU, perform the execution part of a machine cycle. Specifically, the ALU performs the arithmetic, comparison and logical operations.

The system clock

The control unit relies on a small chip called the system clock to synchronize or control the timing of all computer operations. The system clock generates regular electronic pulses or ticks that set the operating pace of components in the system unit. Each tick is called a clock cycle. A CPU requires a fixed number of clock cycles to execute each instruction. The faster the clock, the more the instructions the CPU can execute per second. The speed at which a processor execute instructions is called clock speed or clock rate. Clock speed is measured in Megahertz which is equal to 1 million ticks of the system clock.
The strength of a CPU is determined by how fast it processes data. One of the major factors that affect this is the system clock. A higher clock speed means the CPU can process more instructions per second than the same CPU with a lower clock speed. Or example 700 MHz CPU is faster than 500 MHz.

Coprocessors

Another way to increase the performance of a computer is through the use of a coprocessor, who is a special processor chip or circuit board designed to assist the processor in performing specific tasks. Users running engineering, scientific or graphics applications, for instance, will notice a dramatic increase in speed with a floating -point coprocessor, provided the application is designed to take advantage of the coprocessor. Floating-point coprocessors are also called the math coprocessor or numeric coprocessor.

Parallel processing

Some computers use more than one processor to speed processing times. Known as parallel processing, this method uses multiple processors simultaneously to execute a program. That is parallel processing divides up a problem so that multiple processors work on their assigned portion of the problem at the same time.

Memory

While performing a processing operation, a processor needs a space to temporarily store instructions to be executed and the data to be used with those instructions. A computer's memory in the system unit is used to store data, instructions and information. The memory chips on the circuit board in the system unit perform this function. Memory stores three basic items:

1. The operating system
2. The application program
3. The data being processed

The number of bytes available for use measures the size of memory. A kilobyte is equal to 1024 bytes. The system unit contains two types of memory

1. volatile memory
2. Nonvolatile memory

Volatile memory is lost when the power is turned off whereas non-volatile memory are not lost when power is removed from the computer. RAM is an example of volatile memory. ROM, flash memory, CMOS is examples of non-volatile memories,

RAM

The memory chips in the system unit are called RAM (Random access memory. When the computer power is switched off, the data on the RAM is lost, when power is on, RAM contains, OS, Data and instructions and the application program. RAM is volatile, therefore data on RAM should be saved on secondary storage media like floppy or hard disk (discussed later).

Cache

Memory cache helps to speed the processor of the computer by storing frequently used instructions and data.

ROM

Read only memory is the name given to memory chips storing data that only can be read? That is, the data stored in ROM chips cannot be modified - hence the name read only. While RAM is volatile, ROM is nonvolatile; its contents are not lost when power to the computer is turned off. ROM chips contain data, instructions or information that is recorded permanently. For example, ROM contains the sequence of instructions the computer follows to load the operating system and other files when you first turn the computer on.
The data, instruction or information stored on ROM chips often is recorded when the chips are manufactured. ROM chips that contain permanently written data, instructions or information are called firmware.

Expansion slots and expansion cards

An expansion slot is an opening or a socket where a circuit board can be inserted into the motherboard. These circuit boards add new devices or capabilities to the computer such as more memory, higher quality sound devices, a modem or graphic capabilities. Many terms are used to refer to this type of circuit board: Expansion card, expansion board, and adapter card interface card, card, add-in and add-on.
Three types of expansion cards found in most of today's computer are a video card, a sound card and an internal modem.
A video card, also called a video adapter or graphics card, converts computer output into a video signal that is sent through a cable to the monitor, which displays an image on the screen.
A sound card is used to enhance the sound generating capabilities of a personal computer by allowing sound to the input through a microphone and output through speakers.
An internal modem is a communication device that enables computers to communicate via telephone lines or other means.

PORTS

A cable, often attaches external devices such as a keyboard, monitor, printer, mouse and microphone, to the system unit. The interface or points of attachment to the system unit is called a port. Most of the time, ports are located on the back of the system unit, but they can also be placed on front.

Serial ports

A serial port is one type of port. The transmit data bit by bit, it is usually used to connect devices that don't require test data transmission rates, such as a mouse, keyboard or modem. In a PC, serial port circuits are built into the motherboard.

Parallel port

Unlike serial port, a parallel port is an interface used to connect devices that are capable of transferring more than one bit at a time. Parallel ports originally were developed as an alternative to the slower speed serial ports. Many printers to the system unit use a parallel port with a 25-pin connector. This parallel port can transfer 8 bits of data (one byte) simultaneously through eight separate lines in a single cable.

Power supply

Many PCs are plugged into standard wall outlet, which supply an alternating current (AC) of 115 to 120 volts. The power supply is the component in the system unit that converts the wall outlet AC power into DC power.