Computer System Hardware
Hardware represents the physical and tangible components of a computer i.e. the components that can be seen and touched.
Examples of Hardware are following:-
✱ Input devices -- keyboard, mouse etc.
✱ Output devices -- printer, monitor etc.
✱ Secondary storage devices -- Hard disk, CD, DVD etc.
✱ Internal components -- CPU, motherboard, RAM etc.
Relationship between Hardware and Software
✱ Hardware and software are mutually dependent on each other. Both of them must work together to make a computer produce a useful output.
✱ Software cannot be utilized without supporting hardware.
✱ Hardware without set of programs to operate upon cannot be utilized and is useless.
✱ To get a particular job done on the computer, relevant software should be loaded into the hardware
Hardware is a one-time expense.
✱ Software development is very expensive and is a continuing expense.
✱ Different software applications can be loaded on a hardware to run different jobs.
✱ A software acts as an interface between the user and the hardware.
✱ If hardware is the 'heart' of a computer system, then software is its 'soul'. Both are complimentary to each other.
Computer Memory
✱ Memory is used to store the information (programs and data) that the computer is currently using. It is sometimes called main or primary memory. One form of memory is called
✱ RAM - random access memory. This means that any location in memory may be accessed in the same amount of time as any other location. Memory access means one of two things, either the CPU is reading from a memory location or the CPU is writing to a memory location. When the CPU reads from a memory location, the contents of the memory location are copied to a CPU register. When the CPU writes to a memory location, the CPU copies the contents of a CPU register to the memory
location, overwriting the previous contents of the location. The CPU cannot carry out any other operations on memory locations.
✱ RAM is a form of short term or volatile memory. Information stored in short term storage is lost when the computer is switched off (or when power fails e.g. if you pull out the power lead!). There is therefore a requirement for permanent or long term storage which is also referred to as secondary storage or auxiliary storage. This role is fulfilled by disk and tape storage.
Random Access Memory
RAM(Random Access Memory) is the internal memory of the CPU for storing data, program and program result. It is read/write memory which stores data until the machine is working. As soon as the machine is switched off, data is erased.
Access time in RAM is independent of the address that is, each storage location inside the memory is as easy to reach as other locations and takes the same amount of time. Data in the RAM can be accessed randomly but it is very expensive.
RAM is volatile, i.e. data stored in it is lost when we switch off the computer or if there is a power failure. Hence a backup uninterruptible power system(UPS) is often used with computers. RAM is small, both in terms of its physical size and in the amount of data it can hold.
RAM is of two types
Static RAM (SRAM)
Dynamic RAM (DRAM)
Static RAM (SRAM)
The word static indicates that the memory retains its contents as long as power is being supplied. However, data is lost when the power gets down due to volatile nature. SRAM chips use a matrix of 6-transistors and no capacitors. Transistors do not require power to prevent leakage, so SRAM need not have to be refreshed on a regular basis.
Because of the extra space in the matrix, SRAM uses more chips than DRAM for the same amount of storage space, thus making the manufacturing costs higher. So SRAM is used as cache memory and has very fast access.
Characteristic of the Static RAM
✱ It has long life
✱ There is no need to refresh
✱ Faster
✱ Used as cache memory
✱ Large size
✱ Expensive
✱ High power consumption
Dynamic RAM (DRAM)
DRAM, unlike SRAM, must be continually refreshed in order to maintain the data. This is done by placing the memory on a refresh circuit that rewrites the data several hundred times per second. DRAM is used for most system memory because it is cheap and small. All DRAMs are made up of memory cells which are composed of one capacitor and one transistor.
Characteristics of the Dynamic RAM
✱ It has short data lifetime
✱ Need to be refreshed continuously
✱ Slower as compared to SRAM
✱ Used as RAM
✱ Lesser in size
✱ Less expensive
✱ Less power consumption
Read Only Memory (ROM)
ROM stands for Read Only Memory. The memory from which we can only read but cannot write on it. This type of memory is non-volatile. The information is stored permanently in such memories during manufacture. A ROM, stores such instructions that are required to start a computer. This operation is referred to as bootstrap. ROM chips are not only used in the
computer but also in other electronic items like washing machine and microwave oven.
Following are the various types of ROM
MROM (Masked ROM):-
The very first ROMs were hard-wired devices that contained a pre-programmed set of data or instructions. These kind of ROMs are known as masked ROMs which are inexpensive.
PROM (Programmable Read only Memory):-
PROM is read-only memory that can be modified only once by a user. The user buys a blank PROM and enters the desired contents using a PROM program. Inside the PROM chip there are small fuses which are burnt open during programming. It can be programmed only once and is not erasable.
EPROM(Erasable and Programmable Read Only Memory):-
The EPROM can be erased by exposing it to ultra-violet light for a duration of up to 40 minutes. Usually, an EPROM eraser achieves this function. During programming, an electrical charge is trapped in an insulated gate region. The charge is retained for more than ten years because the charge has no leakage path. For erasing this charge, ultra-violet light is passed through a quartz crystal window(lid). This exposure to ultra-violet light dissipates the charge. During normal use the quartz lid is sealed with a sticker.
EEPROM(Electrically Erasable and Programmable Read Only Memory):-
The EEPROM is programmed and erased electrically. It can be erased and reprogrammed about ten thousand times. Both erasing and programming take about 4 to 10 ms (milli second). In EEPROM, any location can be selectively erased and programmed. EEPROMs can be erased one byte at a time, rather than erasing the entire chip. Hence, the process of re- programming is flexible but slow.
Advantages of ROM
The advantages of ROM are as follows:-
✱ Non-volatile in nature
✱ These cannot be accidentally changed
✱ Cheaper than RAMs
✱ Easy to test
✱ More reliable than RAMs
✱ These are static and do not require refreshing
✱ Its contents are always known and can be verified
Input/Output Devices:-
Input Devices
Following are few of the important input devices which are used in a computer:-
✱ Keyboard
✱ Mouse
✱ Joy Stick
✱ Light pen
✱ Track Ball
✱ Scanner
✱ Graphic Tablet
✱ Microphone
✱ Magnetic Ink Card Reader(MICR)
✱ Optical Character Reader(OCR)
✱ Bar Code Reader
✱ Optical Mark Reader(OMR)
Keyboard
Keyboard is the most common and very popular input device which helps in inputting data to the computer. The layout of the keyboard is like that of traditional typewriter, although there are some additional keys provided for performing additional functions.
Keyboards are of two sizes 84 keys or 101/102 keys, but now keyboards with 104 keys or 108 keys are also available for Windows and Internet.
The keys on the keyboard are as follows:-
1. Typing keys:- These keys include the letter keys (A-Z) and digit keys (0-9) which generally give same layout as that of typewriters.
2. Numeric keys:- It is used to enter numeric data or cursor movement. Generally, it consists of a set of 17 keys that are laid out in the same configuration used by most adding machines and calculators.
3. Function keys:- The twelve function keys are present on the keyboard which are arranged in a row at the top of the keyboard. Each function key has unique meaning and is used for some specific purpose.
4. Control keys:- These keys provide cursor and screen control. It includes four directional arrow keys. Control keys also include Home, End, Insert, Delete, Page Up, Page Down, Control(Ctrl), Alternate(Alt), Escape(Esc).
5. Special Purpose keys:- Keyboard also contains some special purpose keys such as Enter, Shift, Caps Lock, Num Lock, Space bar, Tab, and Print Screen.
Mouse
Mouse is most popular pointing device. It is a very famous cursor-control device having a small palm size box with a round ball at its base which senses the movement of mouse and sends corresponding signals to CPU when the mouse buttons are pressed.
Generally it has two buttons called left and right button and a wheel is present between the buttons. Mouse can be used to control the position of cursor on screen, but it cannot be used to enter text into the computer.
Advantages
✱ Easy to use
✱ Not very expensive
✱ Moves the cursor faster than the arrow keys of keyboard.
Joystick
Joystick is also a pointing device which is used to move cursor position on a monitor screen. It is a stick having a spherical ball at its both lower and upper ends. The lower spherical ball moves in a socket. The joystick can be moved in all four directions.
The function of joystick is similar to that of a mouse. It is mainly used in Computer Aided Designing(CAD) and playing computer games.
Light Pen
Light pen is a pointing device which is similar to a pen. It is used to select a displayed menu item or draw pictures on the monitor screen. It consists of a photocell and an optical system placed in a small tube. When the tip of a light pen is moved over the monitor screen and pen button is pressed, its photocell sensing element detects the screen location and sends the corresponding signal to the CPU.
Track Ball
Track ball is an input device that is mostly used in notebook or laptop computer, instead of a mouse. This is a ball which is half inserted and by moving fingers on ball, pointer can be moved. Since the whole device is not moved, a track ball requires less space than a mouse. A track ball comes in various shapes like a ball, a button and a square.
Scanner
Scanner is an input device which works more like a photocopy machine. It is used when some information is available on a paper and it is to be transferred to the hard disc of the computer for further manipulation. Scanner captures images from the source which are then converted into the digital form that can be stored on the disc. These images can be edited before they are printed.
Digitizer
Digitizer is an input device which converts analog information into digital form. Digitizer can convert a signal from the television or camera into a series of numbers that could be stored in a computer. They can be used by the computer to create a picture of whatever the camera had been pointed at. Digitizer is also known as Tablet or Graphics Tablet because it converts graphics and pictorial data into binary inputs. A graphic tablet as digitizer is used for doing fine works of drawing and image manipulation applications.
Microphone
Microphone is an input device to input sound that is then stored in digital form. The microphone is used for various applications like adding sound to a multimedia presentation or for mixing music.
Magnetic Ink Card Reader(MICR)
MICR input device is generally used in banks because of a large number of cheques to be processed every day. The bank's code number and cheque number are printed on the cheques with a special type of ink that contains particles of magnetic material that are machine readable. This reading process is called Magnetic Ink Character Recognition (MICR). The main advantages of MICR is that it is fast and less error prone.
Optical Character Reader(OCR) OCR is an input device used to read a printed text. OCR scans text optically character by character, converts them into a machine readable code and stores the text on the system memory.
Bar Code Readers
Bar Code Reader is a device used for reading bar coded data (data in form of light and dark lines). Bar coded data is generally used in labelling goods, numbering the books etc. It may be a hand held scanner or may be embedded in a stationary scanner. Bar Code Reader scans a bar code image, converts it into an alphanumeric value which is then fed to the computer to which bar code reader is connected.
Output Devices
Following are few of the important output devices which are used in a computer.
✱ Monitors
✱ Graphic Plotter
✱ Printer
Monitors
Monitors, commonly called as Visual Display Unit (VDU), are the main output device of a computer. It forms images from tiny dots, called pixels that are arranged in a rectangular form. The sharpness of the image depends upon the number of pixels.
There are two kinds of viewing screen used for monitors.
✱ Cathode-Ray Tube (CRT)
✱ Flat- Panel Display
Cathode-Ray Tube (CRT) Monitor
The CRT display is made up of small picture elements called pixels. The smaller the pixels, the better the image clarity, or resolution. It takes more than one illuminated pixel to form whole character, such as the letter ‘e’ in the word help.
A finite number of characters can be displayed on a screen at once. The screen can be divided into a series of character boxes - fixed location on the screen where a standard character can be placed. Most screens are capable of displaying 80 characters of data horizontally and 25 lines vertically. There are some disadvantages of CRT:
✱ Large in Size
✱ High power consumption
Flat-Panel Display Monitor
The flat-panel display refers to a class of video devices that have reduced volume, weight and power requirement in comparison to the CRT. You can hang them on walls or wear them on your wrists. Current uses of flat-panel displays include calculators, video games, monitors, laptop computer, graphics display.
The flat-panel display is divided into two categories:
✱ Emissive Displays:- The emissive displays are devices that convert electrical energy into light. Example are plasma panel and LED(Light-Emitting Diodes).
✱ Non-Emissive Displays:- The Non-emissive displays use optical effects to convert sunlight or light from some other source into graphics patterns. Example is LCD(Liquid-Crystal Device)
Printers
Printer is an output device, which is used to print information on paper. There are two types of printers:
✱ Impact Printers
✱ Non-Impact Printers
Impact Printers
The impact printers print the characters by striking them on the ribbon which is then pressed on the paper.
Characteristics of Impact Printers are the following:-
✱ Very low consumable costs
✱ Very noisy
✱ Useful for bulk printing due to low cost
✱ There is physical contact with the paper to produce an image
These printers are of two types
✱ Character printers
✱ Line printers
Character Printers
Character printers are the printers which print one character at a time. These are further divided into two types:
✱ Dot Matrix Printer(DMP)
✱ Daisy Wheel
Dot Matrix Printer
In the market one of the most popular printers is Dot Matrix Printer. These printers are popular because of their ease of printing and economical price. Each character printed is in form of pattern of dots and head consists of a Matrix of Pins of size (5*7, 7*9, 9*7 or 9*9) which come out to form a character that is why it is called Dot Matrix Printer.
Advantages
✱ Inexpensive
✱ Widely Used
✱ Other language characters can be printed
Disadvantages
✱ Slow Speed
✱ Poor Quality
Daisy Wheel
Head is lying on a wheel and pins corresponding to characters are like petals of Daisy (flower name) that is why it is called Daisy Wheel Printer. These printers are generally used for
word-processing in offices which require a few letters to be sent here and there with very nice quality.
Advantages
✱ More reliable than DMP
✱ Better quality
✱ The fonts of character can be easily changed
Disadvantages
✱ Slower than DMP
✱ Noisy
✱ More expensive than DMP
Line Printers
Line printers are the printers which print one line at a time.
These are of further two types
✱ Drum Printer
✱ Chain Printer
Drum Printer
This printer is like a drum in shape so it is called drum printer. The surface of drum is divided into number of tracks. Total tracks are equal to size of paper i.e. for a paper width of 132 characters, drum will have 132 tracks. A character set is embossed on track. The different character sets available in the market are 48 character set, 64 and 96 characters set. One rotation of drum prints one line. Drum printers are fast in speed and can print 300 to 2000 lines per minute.
Advantages
✱ Very high speed
Disadvantages
✱ Very expensive
✱ Characters fonts cannot be changed
Chain Printer
In this printer, chain of character sets are used so it is called Chain Printer. A standard character set may have 48, 64, or 96 characters.
Advantages
✱ Character fonts can easily be changed.
✱ Different languages can be used with the same printer.
Disadvantages
✱ Noisy
Non-impact Printers
Non-impact printers print the characters without using ribbon. These printers print a complete page at a time so they are also called as Page Printers.
Characteristics of Non-impact Printers
✱ Faster than impact printers.
✱ They are not noisy.
✱ High quality.
✱ Support many fonts and different character size.
These printers are of two types
✱ Laser Printers
✱ Inkjet Printers
✱ Thermal Printer
Laser Printers
These are non-impact page printers. They use laser lights to produce the dots needed to form the characters to be printed on a page.
Advantages
✱ Very high speed
✱ Very high quality output
✱ Give good graphics quality
✱ Support many fonts and different character size
Disadvantages
✱ Expensive.
✱ Cannot be used to produce multiple copies of a document in a single printing.
Inkjet Printers
Inkjet printers are non-impact character printers based on a relatively new technology. They print characters by spraying small drops of ink onto paper. Inkjet printers produce high quality output with presentable features.
They make less noise because no hammering is done and these have many styles of printing modes available. Colour printing is also possible. Some models of Inkjet printers can produce multiple copies of printing also.
Advantages
✱ High quality printing
✱ More reliable
Disadvantages
✱ Expensive as cost per page is high
✱ Slow as compared to laser printer
Thermal Printer
A thermal printer is a printer that makes use of heat in order to produce the image on paper.
Due to quality of print, speed, and technological advances it has become increasingly popular and is mostly used in airline, banking, entertainment, retail, grocery, and healthcare industries. Thermal printing does not make use of ink or toner unlike many other printing forms but largely depends on thermal papers for producing the images. They are also quiet popular in creating labels owing to speed of printing.
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