Computer Hardware



Computer Hardware

When you go near computer, You see that different devices like the monitor, CPU, mouse, printer etc. are connected to each other through wires. These devices are the physical parts of computer. So we can say that the Computer is a collection of many physical parts which are connected to each other with the help of wires and cables. All these physical parts of a computer are computer hardware. Some parts are used to give input, some are used to get output, some are for processing and storing data etc. According to these uses, we group the parts as

Input Devices,

Output devices,

Storage Devices,

Processing device

Figure: Hardware Basic

When we see the computer from inside, we can find that there are many parts. The figure below shows the inside of the computer. We can categorize these parts in a more detailed way.

1) Input Devices

2) Output Devices

3) Processing Device

-CPU

4)Storage Devices

-Primary Memory (RAM & ROM))

-Secondary Storage(floppy Disk, Hard Disk, CD-ROM)

Ports are used for connecting hardware from outside like input and output devices. Buses are used for moving the information from one part to another part inside computer

Input Devices Output Devices

Figure 1: Computer from Inside

Now we will discuss each part in detail.

1) Input Devices:

The data and instructions that a computer receives are called input. An input device is used to give instructions to the computer. It works like our sense organs (nose, eyes, ears etc) which takes in information (by smelling, seeing, listening etc) and send it to our brain. Without the input devices we can not do anything with computer.

There are many input devices like keyboard, mouse, scanner, touch-screen, joystick, light pen, MICR, OCR and OMR. We can group these input units into following types.

Text input devices: Keyboard

Pointing devices: Mouse,touch screen,light pen

Gaming devices :Joystick

image video input devices: scanner, web cam, OCR, MICR, OMR

Audio input devices: microphones

Keyboard: Keyboard is the way to enter data or instruction into a computer. It has different keys for letters of alphabet, numbers, function keys, other keys which move cursor on the screen and special keys. The standard keyboard has 104 keys. Keyboard can be used to type documents and to send instructions to the CPU.

Mouse: It is another common input device. It is also known as pointing device. It can be used to move cursor (a pointer) around the screen, to draw shapes or to make a choice from the menu.

It is made up of small plastic box with buttons on top. On the bottom, some of the mouse have small rubber ball which rolls and control the direction of the pointer on the screen. Another type of mouse uses an optical system to track the movement of the mouse.

As the mouse is dragged on the surface, the movement is converted into data which is sent to the CPU. The CPU uses this data to plot the direction of the mouse’s movement. It sends the signals to the cursor on the monitor screen, which follows the movement of the mouse exactly. The functions of the two buttons on the top of mouse are different. Left one is used to select objects and text and the right one is used to access menus.

Light Pen: It is a pointing device like mouse. Its shape is like a pen. With a light pen, we can move the pointer and select the object by directly touching the object by pen on the screen. It has a light sensitive element on the tip of pen, which detects the location of the pen on the screen. We can also draw on the screen using light pens.

Joystick: Joysticks are similar to mouse. They are mainly used in computer games. They are sometimes used in CAD/CAM systems and other applications. It has a stick that pivots on a base and reports its angle or direction to the device it is controlling. It has one or more buttons which are called trigger and are used to trigger the action.

Scanners: Scanners are like eyes. They see the images or printed text and translate them into binary code. To do this, scanner sends a beam of light to the page and then measures how much light has reflected back. Then the digital code is generated according to the light or dark image and is given to the amount of light for each portion. This code is sent to the CPU, which then creates an image. They are used to input pictures or small portion of a page.

Touch Screen : A touch screen is becoming very popular input device these days. By using touch screen monitors, user can operate a computer by simply touching the monitor. Touch input is suitable for a wide variety of computing applications. We can select options and give commands by pressing different areas on the screen. A touch screen are sensitive to the touch of a finger. A touch-screen system is made up of a touch sensor, a controller card, and a software driver. When we touch the screen area, the touch screen panel registers this touch events and passes these signals to the controller. Then the controller processes the signals and sends the data to the processor. The software driver translates touch events into mouse events.

OCR (Optical Character Reader) : This device is used for the data entry purposes. It uses one of the two following methods:Matrix matching method and feature extraction method.

In matrix matching method, When the OCR scanner reads data, Matrix matching takes the data as a character and compares this character with a set of stored character matrices or templates. When an image matches one of these prescribed matrices of dots within a given level of similarity, the computer labels that image as the corresponding ASCII character.

In Feature extraction method, When the OCR scans the letters, scanned letters are condensed into their basic features. Then the basic features of a letter are compared to a list of features stored in a program's code. If the features matches, the letter is recognized.

For example: the letter "a" is made from a circle, a line on the right side and an arc over the middle. The arc over the middle is optional. So, if a scanned letter had these "features" it would be correctly identified as the letter "a" by the OCR program.

MICR: It stand for Magnetic Ink Character Recognition. It is pronounced as my-ker. It is character recognition technology used mainly by the banks to facilitate the processing of cheques. You must have seen a cheque having a number at the bottom. That number uses special magnetic ink. Writing style is also different. Magnetic ink is used so that character can be read into the system even when they are overprinted by the other marks like cancellation stamp.

Characters in magnetic ink are read by a special machine. This machine changes these characters into code, so that the computer can verify the characters for its duplication.

OMR: It stands for Optical Mark Recognition. It reads different marks, codes, and then convert them into computer readable code. The most common application of this device is the use of 2 HB pencil and bubble optical answer sheet in multiple choice question examinations. Students mark their answers, or other personal information, by darkening circles marked on a sheet. Afterwards the sheet is automatically graded by OMR scanning machines.

Web Cam: It is a small camera, which gives an image as an input.

Micro phone: It is used to give voice input to the computer. It is connected to the sound card in the computer It provides input by converting the sound into electrical signal.

Output Devices:

Anything that provides us with information is output device. In a computer, the Output is an information that it produces. In the computer, the output is in the form of binary code. Output devices, such as printer, monitor and speaker displays it in a way that we can understand. Output can be displayed on the screen or printed on a paper or can be heard on the speaker. Printed output is called hard copy. Output on the screen is called soft copy.

Output devices can be categorize into following types:

Image/video output devices: Printer, Monitor

Audio output devices: Speaker, headphones

Printer: Its an output device It takes what you see on the computer and prints it on the paper or transparency. Printed output is also called a hard copy . Printer uses ink to put data on paper or transparency. There are many types of printers.

1)Dot Matrix Printer

2)Ink Jet Printer

3)Daisy Wheel Printer

4) Laser Printer

Speed of the printer is measured in cps(character per second),lpm(line per minute),ppm(pages per minute). The quality of the print is measured in dpi(dots per inch). Some printers can print in color also. Dot matrix, ink jet and laser printers are most commonly used printers. Printer can be classified into two categories according to the technologies used in them. Impact printer and non-impact printer. An impact printer uses a device to press/strike something against the ribbon to put a character on the page. Dot matrix, daisy and line printer are impact printers.

Non-impact printers print without having a mechanism to strike against a sheet of paper. Ink jet, laser and thermal printer are non-impact printer.

Dot Matrix Printer: It uses dots to form a characters on a paper. Dots are made by pins. Dot matrix printer is made up of steel pins which strike the paper through a inked ribbon to create a pattern of tiny dots. The quality of print depends upon the number of steel pins in the machine.

Daisy Wheel printer: In this type of printer, the part that puts the characters looks like a wheel. Numbers and letters are arranged in a wheel. And the daisy wheel spins until the correct letter is in position. Then hammer strikes the character against the ribbon, printing it on the paper.

Line Printer: It prints a complete line of text at a time. It uses drum or chain with all the characters in the character set on it. The drum or chain moves and prints the necessary characters in the right place.

Ink jet printer: It prints the character using fine jet of ink which comes out from the tiny nozzles onto the paper. The ink is kept in reservoir and fed into the firing chambers just below each nozzle.

Laser Printer: It uses a beam of light (laser beam) to convert binary data into print. The laser puts an electric charge in the shape of a character on the rotating drum. The dry ink or toner stick only to the drum where it has been charged. These printers are very fast. They can print a whole page at once.

Thermal Printer: It uses heat to put the characters on the paper. The paper has a spacial coating on it. The printer uses heated wires to turn the paper black. It is basically used for taking ECG in hospital or lab.

Plotter: Plotter is a special type of output device designed to produce high quality graphics in a variety of colors.

Monitor: It is a visual display unit (VDU), often called a monitor. Computer generates data or output which can be displayed on the monitor. It is an electrical device and looks like a television screen. There are two types of monitors: CRT monitor and LCD Monitors. CRT Monitor uses picture tubes also called cathode ray tube ( picture tube is used in television) to display information or image on the screen. Generally these monitors are large and bulky due to this picture tube. It also require relatively high voltage power supply.

Because of the high voltage requirement and bulky size, A newer monitors have been developed and used these days with new technology. They use flat panel LCD (liquid crystal display) display in place of cathode ray tube. They are very thin and light weight.

Speaker: Speakers are output devices which produce sound. They are just like a stereo speakers.

Storage Devices

The most important feature of computer is its storing capacity. Memory is the place in the computer where information can be stored. Every computer has two kinds of memory. Primary memory and secondary memory. When we use any program, the computer loads the program from hard disk (secondary memory)to faster memory RAM (Primary memory). We perform the operations while the program is in RAM. The data gets written back to hard disk(secondary memory) when we save or quit the program,

Primary memory: Primary storage, or memory, is directly accessible to the CPU. The CPU continuously reads instructions stored in the memory and executes them. It has two parts: Read Only Memory(ROM) and Random Access Memory(RAM).

RAM: When we enter data from keyboard, the data is first read by the RAM. The output is also stored in RAM. But the information will be stored in it as long as computer is on. When the computer is switched off, all the data stored in it is lost. That is why it is called temporary or volatile memory. It is called Random Access Memory because the computer can pick out or access any piece of data from any location of memory.

ROM: This memory is used to store things which are never going to change. In ROM data or program can not be written or stored but only can be read. The instructions can not be changed, and they won't be wiped out when the computer is turned off. That is why this memory is called permanent or non volatile memory. This memory is used to store the program like operating systems . When the computer is switched on and it is starting up, the instructions stored in ROM tells the CPU how to go ahead.

Secondary Memory: Primary memory or memory is a temporary memory and when we turn off the computer, programs and data present in the memory get erased. When we are sharing the computer, we must yield the memory to someone else to run the program. Also , we want to store data and programs we have processed in computer. So we need to have some permanent storage.

To store the data permanently, secondary memory is used. secondary memory is used to store large amount of data permanently as compared to primary memory. There are various types of secondary storage devices available like, floppy disk, hard disk, CD-ROM, pen drive etc.

Floppy Disk: Floppy disk is a circular thin plastic jacket coated with magnetic material. It is covered with a hard plastic cover to protect this disk. It stores information magnetically on one or both sides. This is very useful in transferring data from one computer to another. Most floppy disks are 3.5 inches in size. Floppy disk drive should be present in computer for reading or writing data in floppy disk. These days, floppy disks are not used much.

Hard Disk: Hard disk is a solid, rounded disk made up of magnetic material and placed inside the computer. They do exactly the same thing as floppy disk, except that its storing capacity is more. The information stored in hard disk is permanent until we erase it.

Optical Disk Storage: Optical disk technology is categorized by its read/write capability. It uses the following technology: In these kind of disks, a metallic material is spread over the surface of the disk. A laser heats the surface and when the data is entered, due to the laser heat, tiny spots are created on the surface of disk. To read the data from disk, laser scans the disks, and the lens picks up different light reflections from the various spot. CDs( compact Disk) come into this category.

CD-ROMs are one type of CD, in which we can't write or change anything. We can only read. CD-ROM are recorded on by the manufacturer. Such a disk can not be used for our files, but manufacturers supply the softwares in CD-ROM. It is like a compact disk we buy from music store and tt is a read-only disk. It means that it can't be erased or written by the user.

It can store much more information than floppy disk. We need to have a CD-drive installed on computer to read from CD-ROM.

In CD drive, we get write CD drive or CD-RW as an option. CD-RW is a write once and read many times media. With a CD-RW drive, we can store our data. This is an convenient, inexpensive and safe way to store large volume of data.

DVDs: Digital Versatile disk(DVD) are now widely used in computers. Data are stored just like in CDs. DVD disks are read by laser beam of shorter wave length than used by the CD-ROM, which allows increased storage capacity in DVDs.

USB Pen Drive: It is a flash memory data storage device integrated with USB( Universal serial port) interface. It is removable and rewritable, much smaller than a floppy disk (size:1 to 4 inches or 2.5 to 10 cm), and weighs less than 2 ounces (60 g). Its storage capacity ranges from 64 MB to 32 GB. It is compact, faster, and holds much more data. Its design is more durable. To access the data stored in a flash (pen) drive, the drive must be connected to a USB port built into a computer.

Processor:

Figure: Central Processing Unit

Central Processing Unit (CPU):There is a main part of computer that takes input , processes the data and gives output. This part is called central processing unit (CPU). It is a highly complex electronic circuitry. All the computers have a central processing unit. CPU has direct relationship with Primary memory. The CPU interacts closely with primary storage, or main memory, for instructions and data. Data is stored in main memory temporarily, while the CPU is executing a program. But, memory is not part of the CPU.

CPU has two parts: The control unit and the arithmetic/logic unit. Each part has a specific function.

Control Unit: They are the in charge of computer. The control unit directs the flow of information to entire computer system or to execute the instructions. Control unit is like a leader of the music concert. In the music concert, leader does not plays the music but controls and instruct the group to perform. Similarly, the control unit does not execute program instructions; it directs the other parts of the system to do so. The control unit communicates with both the arithmetic/logic unit and memory.

Arithmetic/Logic unit(ALU):The arithmetic/logic unit executes all the arithmetic and logical operations.

The arithmetic/logic unit can do all the mathematical calculations: addition, subtraction, multiplication, and division. It also performs logical operations. A logical operation is basically a comparison of values. It can compare numbers, letters, or special characters. some common logic comparison symbols are

= equal to

< less than

> greater than

= greater than or equal to

not equal

The computer can take action based on the result of the comparison. This is a very important capability. By comparing computer can tell, for instance, whether there are seats available on Train to go to particular place, whether person has exceeded the quota of issued books in library.

How the CPU Executes Program Instructions:

Before the execution of a program, the program data and instructions are moved into the memory from input device or from secondary storage device. Then the CPU performs the following steps.

1. The control unit first gets the instructions from memory. It checks what the instruction means and accordingly sends the necessary data from memory to arithmetic/logic unit.

2. The arithmetic/logic unit then performs the actual operation on data and stores the result back in the memory.

When the results are in memory, then the control unit tells the memory to send the result to an output device or a secondary storage device. The above process is shown in the figure 2.

Figure: Execution in CPU

I

-----------------------

Processing Device(CPU)

Input Device

Output Device

Storage

Device

PORTS

Mother Board

Processor

(CPU)

BUS

RAM

HARD DRIVE

CD_ROM

FLOPPY

DRIVE

Central Processing Unit

Control

Unit

Arithmetic

Logic Unit

Memory

Input

output

Secondary memory Programsecondary memory

Control Unit

2) Decode and send to ALU

1)Get the instruction

Arithmetic/Logic

Unit

3)execute

4)store

Memory

ROM

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