INTRODUCTION

    Computer is an electronic device. As mentioned in the introduction it can do arithmetic calculations faster. But as you will see later it does much more than that. It can be compared to a magic box, which serves different purpose to different people. For a common man computer is simply a calculator, which works automatic and quite fast. For a person who knows much about it, computer is a machine capable of solving problems and manipulating data. It accepts data, processes the data by doing some mathematical and logical operations and gives us the desired output.

Architecture of Computer:

FEATURES

Speed: Computer can calculate complex calculation at a very high speed. Computer takes a few micro/nano second to execute as operation.

1 Millisecond =1/1000th of a second.

1 Microsecond = 1/1000000th of a second

1 Nanosecond = 1/1000000000th of a second

1 Picosecond = 1/1000000000000th of a second

 Accuracy: If the data and instructins given are correct, the result given by the computer will always be accurate. The term GIGO ( Garbage in Garbage Out) applies in theis context as: if we give the wrong data then the computer will obviously give us wrong output.

 Diligence: Deligence is a capacity of performing repeated operation without any tiredness and any mistakes. A computer is capable of performing the required task continuously with the same speed, accuracy and efficiently without any error. Computer never gets tired, bored and laziness to do the task.

 Versatility: Versatility is an ability to perform various task related to different fields like Science and Technology, Business, Education etc. Such as a doctor could not design a building architecture and an engineer could not make any surgery but the same computer could be use in both of the field.

 Memory power: A computer system can store a great amount of data. Computer has inbuilt and auxiliary memory. The data stored in the computer disk can be modified at the required time.

GENERATION OF COMPUTER

    In 1960’s decade a convention was organized to clarify the generation of the computer by the compute scientists. At that time Two main components of the computer Memory(Storage) and Processing devices were taken to divide the generation. Now, computer are defined in five generations.

TYPES OF COMPUTER

Basis On Model

Advanced Technology (AT):

Advanced Technology Extended (ATX)

Personal System / 2 (PS / 2)

Basis On Brand

IBM

IBM compatible

Apple Macintosh

Basis On Work

Analog Computer :

              
   The computer which can process continuous variables only is the analog computer. The speedometer of motorbike, analog thermometer etc. are the examples of the analog computers.

Digital Computer :

    The Digital computer can process discrete variables only. Most of the digital calculators are the example of the digital computer.

Hybrid Computer :

    The Hybrid computer can process continuous as well as discrete variables. The computer which is used in jet planes and fighter planes is the hybrid computer.

Basis On size / speed

Super Computer:

     Super computers are the most powerful and faster of all computer system. Supercomputer are even faster then the mainframes. The supercomputers are being used in the complex scientific calculations and research project. The supercomputers are important innovation in history of computer. They may be employed in massive data processing, solving very complex problems. Supercomputers are used in weather forecasting, rock launching, seismology, nuclear physics, weapon research and so on. The cost of these computers are very high (more than 15 million dollars). CRAY I, CRAY X-MP, HITAC S-300 etc. are the popular super computers.

Main frame computer:

     Mainframe computer is larger than mini computer and smaller than supercomputer. It is very popular in database field. It is also applied as web server. It can support more than 1000 processors at the same time.

Mini computer :

    The mini computer is larger in size comparing microcomputer but it has a big storage capacity and processing capabilities. The compute is mostly used in connection more terminal or workstations. Workstations are points where the workers work sharing a single computer as the file server. A minicomputer may have as many as 100 or more terminals connected to it.

Micro computer:

    A computer which is based on the microprocessor, is called a microcomputer. It is small, low cost digital computer. Microcomputer has a microprocessor on a single chip, which is its Central Processing Unit(CPU). It also has other units like input devices memory unit. It is also called personal computer. IBM PC, Apple macintosh etc. are the microcomputers.

Microcomputer are as follows:-

Desktop Computer

Laptop Computer

Note book

Palm top

HISTORY OF COMPUTER

1. ABACUS:

    The ABACUS was the first calculating device of the world, which was first introduced in middle Asia (China) nearly 3000 BC. The ABACUS is a portable device that consists of beds strung on wires or wooden rods.

   The ABACUS has two parts divided by middle bar. The above part is known as heaven and the lower part is known as Earth. Each ball of the heaven part takes value 1 and each ball of earth part takes value 5 in calculating.

2. Napier’s Bone:

The Napier’s Bone was developed by Scottish mathematician John Napier in 1614 AD. It is very helpful to calculate long number mathematical calculations. It has 11 rods with sequenced numbers.

3. The Slide Rule:

    The Slide Rule was invented by William Oughtred in 1617 AD. The device was made on the principle of logarithms. This device consists of tow graduated scales. One of the scales passes over the other. The scales are devised in such a way that suitable alignment of one scale against the other makes it possible to obtain products, quotients or their function by inspection. The slide rule was used by the engineers till 1970s. This was replaced by calculator.

4. Pascaline:

    The pascaline was developed by French mathematician Blaise Pascal in 1642 AD. This machine had a capacity of adding or subtracting 8 column numbers up to 999999999. This machine could add and subtract only.

5. Leibniz’s Calculating Machine:

    The leibniz’s calculator was developed by German philosopher Gottfried von Leibniz in 1671 AD. This machine is also known as stepped calculator. It can calculate addition, subtraction, multiplication, division and square root etc.

6. Difference Engine:

    The Difference Engine was developed by English Mathematician Charles Babbage in 1823. The difference engine was with mechanical memory. Later he design a bigger machine which could compute up to 20 decimal places, called analytical Engine in 1830s. This machine was made to solve differential equations. Since Charles Babbage contributed to develop actual calculating device, he is considered as the Father of Computer.

7. Dr. Herman Hollerith:

      Herman Hollerith designs a system system to record census date in 1881. The information stored as holes in cards, which are interpreted by machines with electrical sensors. Hollerith starts at company named Tabulating Machine Company that will eventually become IBM, Which is the most popular computer company of the world. Hollerith proposed a mechanized method to count the census, which was based on punched cards. The cards were punched by a machine called Punched Card Machine or Hollerith’s Tabulaing Machine.

8. Howard Aiken:

      Next important event was added in the History of computer in 1930. MARK I the first elecromechanical compute was designed by Haward Aiken in 1944 which has the power to support 23 digits. It was build by combining more then 7 lakh separate parts and nearly 500 million wires. It has the power to perform 3 calculations per second.

9. ENIAC

      The ENIAC is the acronym of Electronic Numerical Integrator And Calculator. Which was designed by John mauchly and presper Eckert in 1947. It was formed by combining more than 18000 vacuum tubes, more than 70000 resistors, more than 10000 condensers and more than 6000 switches.

10. EDVAC:

    The EDVAC is the acronym of Electronic Discrete Variable Automatic Computer, which was developed by John Mauchley and John Presper Eckert with the help of Goldstine Neumann in 1949. This machine was used to store the data and information as well as the instruction.

11. EDSAC:

12. UNIVAC:

      The UNIVAC is the acronym of Universal Automatic Computer which was developed by the company founded by mauchley and Eckert in 1951. It became the first commercially used electronic computer of the world.

COMPUTER DISPLAY

The computer display is divided into many types. Some of the main display types of are listed below:

1. CRT(Cathode Ray Tube) Display:

     Video display terminals are the most popular I/O devices used today in direct-access processing applications. Cathode ray tube message and the processed output from the computer. The information regarding bits are displayed on the monitor in character form which we see as alphanumeric characters. Only the characters can be seen on the screen the higher is the resolution or better is the character display or graphics display. The CRT has the 24 lines rows and 80 screen that can be turned on or off to help create an image)

2. LCD (Liquid Crystal Display):

     The display in which liquid crystals and polarizer can manipulate light to charge the liquid crystal cells that provide the display. Such type of display is used in the portable computers, like laptop computer.

3. Resolutions:

The number of pixels produces the resolution in the screens. The resolution depends on the monitor and the display adapter installed on the computer. In the screen, the high resolution increases the area of the desktop but decreases the size of the items but the lower resolution increases the size of the items and decreases the size of the desktop.

Some of the resolutions are listed below:

• 640 by 486 pixels
• 720 by 480 pixels
• 720 by 576 pixels
• 800 by 600 pixels
• 1024 by 768 pixels
• 1152 by 864 pixels
• 1280 by 1024 pixels
• 1600 by 1200 pixels

The above resolutions are applied according to the size of the monitor.

COMPUTER HARDWARE

    All the physical components of the computer which can be see and touch are the hardware parts of the computer. All the peripheral parts attached with the computer are known as the hardware parts of the computer like Monitor, Mouse, Keyboard, CPU, Speaker etc. (See Input devices, Output devices, Storage devices)

COMPUTER SOFTWARE

     The computer software is a set of instructions which makes the hardware parts workable. Generally we can compare the software with oxygen for the human body. As the oxygen needed for human body the software instruction needed the computer hardware to run properly.

The computer software can be divided in three main parts.

I. Application Software:

    Those softwares which has particular task are the application software like documentation, presentation, publication etc. Microsoft word, Excel, PowerPoint, Adobe PageMaker, Photoshop etc are the application softwares.

II. System Software

A. Language Processor:

    The language processor is also a powerful part of the system software which translates different programming codes as required. The language processors can be defined as follows

1. Interpreters:

    The interpreter is a program that translates user’s programming language to high lever languages into machine language code and fetches them to the computer to execute. Interpreter translate one statement at a time.

2. Assembler:

    The assembler is the software which translates programs written in assembly language into machine code, which the computer understands. One assembly instruction is converted into machine instruction.

3.  Compilers:

    The compiler is a program that translates use’s programming languages or high level languages into machine language code and fetches them to the computer to execute just like the interpreter. Unlike interpreters, compilers translate the whole program instead of the one program instruction.

B. Utility Software:

    The software which checks the system and manages file to make the system up to date is the utility software. It works as the doctor of the computer. It any error occurs on the computer it automatically fixes it. All the antivirus programs, System tools etc. are the utility software.

C. Operating System:

The operating system is the master controller of the computer system. The operating system creates link between hardware and the application software of the computer. It controls entire system and creates environment for different application software.

Operating system can be divided in two main parts.

1. Command line User Interface(CUI):

     In command line user interface the command must be typed for each and every action. MS DOS is the popular CUI operating system. In CUI The user must close the running file to open next new file, user could not work with multiple application at the same time. In CUI Operating system user could not use any pointing device like mouse, touch pad, track ball etc.

2. Graphical User Interface:

     In Graphical User interface the user can apply any command or action by the help of pointing devices. Windows, Mac OS are the popular graphical operating systems. In graphical operating system the user can work with multiple applications at the same time, which is known as multi tasking.

MS-DOS ( MICROSOFT DISK OPERATING SYSTEM)

     Microsoft DOS (Disk Operating System) is a command line user interface. MS-DOS 1.0 was released in 1981 for IBM computers and the latest version of MS-DOS is MS-DOS 6.22, which was released in 1994. While MS-DOS is not commonly used by itself today, it still can be accessed from every version of Microsoft Windows by clicking Start / Run and typing "command" or by typing "CMD" in Windows NT, Windows 2000 or Windows XP.

Some points before MS-DOS

1.  Drive Prompt: The drive prompt defines the drive in which you are working.

A: First Floppy Disk Drive

B: Second Floppy Drive

C: First Partition of the hard disk drive.

D: Second Partition of the hard disk drive.

The last drive (Generally E: or F: ) : CD ROM Drive

2. Directory: Directory defines the root or path where you are creating files or directories. You can store sub-directories and files in a directory. In windows operating system It appears as a folder.

3. Path: path also defines the root where you are creating directory or file. It begins with drive prompt and displays all root directories name to reach to the current directory.

4. Wild Cards: In MS-DOS you can use some characters for special purpose, which are known as wild cards.

   * (Astrik sign) : Which defines group of character.

    ? (Question mark) : Which defines individual character.

   # You can use these wild cards if you need to copy, cut or delete files or directories having same          filename or extension.

5. Filename : It defines the name of the file. You could not create more than two files having same name with in a same directory. It supports only 8 characters as filename.

6. Extension: It defines the nature of the file. As people has different cast same as computer files has different extensions for different applications, files.

.sys : System files
.bat : Batch files
.exe : Executable file
.dll : Dynamic link library files.
.doc : Document file (Microsoft Word)
.xls : Worksheet file (Microsoft Excel)
.ppt : Presentation file (Microsoft Powerpoint)
.gif : Graphics Interchange Format (Image file)
.jpg : Joint photographic expert group (Image file)
.png : Portable Network Graphics (Image file)
.htm/.html: Hyper text markup Language (Webpage format file)
7. System file : Those file having extension .sys, which are required to boot the computer are known as system files. In MS-DOS Three files are required to boot the computer
IO.SYS
MSDOS.SYS
COMMANDCOM.SYS

Limitations of MS-DOS

1. It is a command line user interface (CUI) operating system. You must type commands from the keyboard for each and every action.

2. It is a single user Interface operating system and It doesn't support multitasking. You must close first file to open next file in MS-DOS.

3. It accepts only 8 characters as filename and 3 characters as extension.

4. It doesn't support some symbols as file name and extensions like \,/, . , ! , | , , , etc.

MS-DOS accepts two types of commands which are Internal DOS commands and External DOS Commands.

Internal DOS command:

Those commands which are included in COMMANDCOM file and which can be run from any drive prompt are the internal DOS commands. Internal DOS commands always remains at the computer memory after booting so we can run from every drive prompt.

External DOS Commands:

    Those commands which are not included in COMMANDCOM file and which reside on the system disk are the external commands. The system disk must be in the same drive to work with external DOS commands.

MICROSOFT WINDOWS

Introduction

Windows 98 is an operating system which is developed Microsoft Company to overcome the problems of earlier windows programs like windows 3.1, windows 95, windows 98, windows 2000, windows XP, windows ME. It makes our computer easier to use with new and enhanced features. The tools of windows 98 help our computer to run fast with out adding any new hardware. It also makes our computer more entertaining by introducing new features such as enhanced television, video, playback and support for new hardware. It supports many devices like printers, scanners, etc.

What is desktop ?

When we power on the computer, after few minutes computer will display some icons like my computer, Recycle Bin, My Document .etc

How to create new folder on desktop?

v            Click right mouse button in the blank area of desktop.

v            Click on New, click on “Folder”.

v            Then type the name for folder.

v            Click on enter key or click on blank area.

To open the files or Folders

v            Select the required files or folders you want to open.

v            Click on right mouse click on open.

Or

v            Double click the file or Folder, which you want to open.

To create new File in the Folder.

v            First open the folder, click on File menu.

v            Click on New command

v            Then choose the required option. (Word document, excel, worksheet etc)

To open windows explorer.

v            Click on start button.

v            Click on programs.

v            Click on windows explore.

Or

v            Right click on the start button.

v            Click on explore.

(The left side of the windows explorer window contains a list of your drives and folders and the right side displays the contents of a selected folder)

To copy files or folders

v            Click on right mouse button and click on copy.

v            Now, open the drive or folder where you want to put the copy.

v            Click on Right mouse button again, click on paste.

To delete files or folder

v            Open windows explorer.

v            Select files or folders you want to delete.

v            Press the right button of mouse.

v            Click on ok.

v            Then a confirm dialog box appears.

v            Click on yes button.

To Restore Files or Folders From Recycle Bin.

v            Open Recycle bin.

v            Select the required Files or Folders.

v            Press the Right mouse button.

v            Click on Restore.

To make Recycle Bin Empty

v            Select the Recycle bin

v            Press the Right mouse button.

v            Click on Empty Recycle Bin.

To put the shortcuts on desktop.

v            Press the right mouse button in the blank area of desktop

v            Click on New and click on shortcut.

v            Then a dialog box appears.

v            Click on Browse button

v            Close the required Files or Program name

v            Click on open button.

v            Click on Next button

v            Type the name for shortcuts and click on Finish.

To Find Files or Folders.

v            Click on start button and go to find.

v            Click on files or folders

v            The dialog box appears. Type the name of files, folders or program or type the starting characters with wildcards (*.doc, *.xls, *.jpg, *.bmp, *.tmp, etc)

v            Click on find next button.

To Add/Remove programs from start on program menu.

v            Click on start and click on settings.

v            Then click on Taskbar & start menu.

v            Click on start menu programs tab.

v            Click on Add button and click on browse.

v            Locate the program you want to Add, and then click it.

v            Click Next and then double click the menu on which you and to program to appear.

v            Type the name that you want to see on the menu and the n click on Finish.

To open Notepad.

You can see notepad to create or edit text files that do not require formatting.

v            Click on start button

v            Click on programs

v            Click on Accessories.

v            Click on Notepad.

To open WordPad.

WordPad is a text editor for short document, you can format save, print the documents for personal and business use.

v            Click on start button

v            Click on programs.

v            Click on Accessories.

v            Click on WordPad.

To Set Date & Time.

v            Click on start

v            Click on settings.

v            Click on Control panel.

v            Double click on date & Time.

v            Then a dialog box appears.

v            Double click the required month, year, date, and time.

v            Click on Apply, click on ok.

To Change the Mouse Settings.

v            Click on start and click on settings.

v            Click on control panel

v            Then double click on Mouse.

v            Now a dialog box appears.

v            Set the required options

v            Click apply and click on ok

To check the disk for errors.

v            Click on start button and click on programs.

v            Click on Accessories, and click on system tools.

v            Click on scandisk.

v            Then a dialog box appears.

v            Select the drive (c: a:,d: etc)

v            Choose the type of test.

v            Click on Automatically Fix errors.

v            Click on start button.

To Change the Background of Desktop

v            Click on right mouse button in the blank area of desktop.

v            Click properties, then a dialog box will Appears.

v            Click on background tab.

v            Choose any picture or web document.

v            Choose any display option (stretch, tile, center)

v            Click on Apply and click on ok

To Apply Screen Saver

v            Press the opposite mouse button in the blank area of desktop.

v            Choose properties.

v            Then a dialog box wills Appears.

v            Click on screen saver.

v            To Apply text as screen saver, choose 3d Text

v            Click on settings and type the required text or your name.

v            Choose the required size, resolution, speed, spins style, font etc.

v            Click on ok.

v            Choose the required timing from wait option.

v            Click on apply.

v            Click on ok.

To Change the Appearance of windows

v            Press the opposite mouse button in the blank area of desktop.

v            Choose properties and then a dialog box appearance.

v            Click on Appearance tab.

v            Choose any time and scheme.

v            Click on Apply, Click on OK.

Calculator.

- Input the non-calculation items by tab setting.

- Load calculator with the following procedure.

Process:

v            Click on start

v            Click on Program

v            Click on Accessories

v            Click on Calculator.

In the absence of short cut, run the program as below.

Process:

v            Click on Start

v            Click on Run

v            Calculate the item using calculator and copy it.

v            Click on Ms WordPad to the right destination and paste it. Repeat the same steps till all the items are calculated.

MULTI-MEDIA:

          The multiple mediums of communication are known as multi-media in computer terminology. We use different types of mediums in communication. That may be textual information video clips, audio or video. It is found one of the fastest and casualty ways of communication in modern technology. In this chapter, we will learn how to play the audio and video.

          A multimedia computer should have the following peripheral devices: Pentium I having 100MHz(Minimum)

AGP Display.

1GB of Hard disk

Sound card

Modem (modulator and Demodulator)

64MB RAM (Random Access Memory)

CD-Drive:

Playing Audio CD:

Insert the audio CD into the CD ROM Drive.

Load the program in the given path.

v            Click on Start

v            Click on Program

v            Click on Accessories

v            Click on Entertainment

v            Click on CD-Player

After detecting the drive and music tracks, the main window will be active. Click on the control button such as play, rewind, and forward stop and eject as usual in our cassette player.

Playing Videos:

Repeat the same steps as usual with the given steps.

Process:

v      Click on Start.

v      Click on Program.

v      Click on Accessories.

v      Click on Entertainment.

v      Click on Media Player.

v      Choose file then open. Now locate the drive that may be either D:\> or E:\> according   to the partition of the disk.

v      Double click on Mpgav main folder and locate the fill to be played.

Control Panel

          It is the main controlling unit that coordinates and controls the peripheral devices. In other words, it's the main controlling section form where the system settings and options are changed. It's a way of creating a favorable working environment as per the user's interest. Installing and removing program, hardware components and their drivers, new font, changing the screen display setting of mouse, multimedia, keyboard and sound all are performed using control panel. Once the settings are changed form control panel the effect can be obtained from any of the windows associated program.

Loading Control Panel:

v                              Click on Start

v                              Click on Settings

v                              Click on Control Panel

v                              In the absence of the short cut,

run the program as below.

v                              Click on Start Bottom.

v                              Click on Run and display the dialogue box

After having displayed the icons of control panel, double click the respective one and change the settings accordingly.

After having displayed the icons of control panel, double click the respective one and change the settings accordingly.

MICROSOFT WORD PAD

           It is a word processing application program, which developed by the Microsoft Corporation. It's the simple but common word processing application that lads us create simple documents such as a letter, application and report. After having the good concept of WordPad. We can easily run the advanced applications. It's the preliminary platform of word-processing, which is available as the window has been installed or it is a small processing of Microsoft word.

Loading word pad.

v                  Click on Start.

v                  Click on Program

v                  Click on Accessories

v                  Click on Word-Pad

In the absence of the shortcut, run the program as below,

v            Click on Start

Click on Run

Immediate after that a standard word processing screen is appeared.

What is Cursor?

                It's the vertical blinking line, which can be defined as the tip of the pen. It's the main indicator that should be before data insertion and manipulation. It can be easily moved from one place to another with the help of the following key combination.

Editing Text:

                An editing is the process of changing the physical values either adding or removing the text.

Searching a string:

          The process of finding a particular term that has been repeated many times on the document is etymologically said to be searching a string. Especially to note down the position and order of execution, such items are sleeked.

v            Position the cursor at the beginning of the document.

v            Choose find on the edit main menu and specify the string as below.

v            Type the finding word or letter in find what criteria.

v            Click on find next many times till the entire terms are sleeked.

Replacing a String:

          After the particular term has been sleeked successfully may be replaced by a new term, which is performed through replace in global correction and manipulation. After we specify the both of searching and replacing strings, one by one will be replaced conditionally.

v            Choose replace on the edit main menu and specify the both of searching and replacing strings as below:

v            Click on replace for individual while replace all, global replacements.

Paste Special:

                With the use of simple paste, the whole attributes can be copied with no options. By using paste special we can highlight only the selected attribute. It has the following common attributes.

v            Highlight the preformatted item and copy it.

v            Position the cursor and choose paste special then any of the following attributes.

Inserting Date and Time: If the system date is correct, it shows the current date in different styles. From which where the right one we can select accordingly.

v            Locate the cursor and choose date and time on the insert main menu.

v            Choose any of the following date and time format.

Inserting an object:

                No program in software industry is self-executable and independent from all aspects. The feature available in one program may not be other. In this respect, the new feature has to be added as an object. The object may be a picture, freehand, interactive image, chart and diagram, metafiles or simply a document extracted form the relative sources.

v            Click on Insert Menu.

v            Choose the Object, then a dialogue box will display.

v            Choose the Microsoft Clip Art Gallery 

v            Then Picture dialogue box will display

v            Choose the any one picture

v            Click on ok.

Posses a head by following necessary steps then choose exit or return to Ms-WordPad on the file main menu after a complete object has been created.

Formatting Letters:

   The process of changing the physical attributes and appearance of the selected text in terms of the letter type, size, style and other initials is called formatting letters in computer terminology. If all the information is uniform, then we can't distinguish between them.

v            Highlight the part of document and choose fonts on the format main menu. Now specify the letter type, style and necessary initials as below:

Formatting a Paragraph:

Naturally, to be a complete document, there may be different paragraphs. If all of them are uniform, we can't locate the selected one more easily. The paragraph may constitute the alignment and indentation form left, right and first line.

v            Locate the paragraph and choose paragraph on the format main menu. Now specify the alignment and indents as below:

Note: To format two or more paragraphs, all of them should be highlighted first.

Tab Setting:

                When we press the tab key, initially the cursor moves 4 characters right wards with left alignment. By using tab setting, we can specify the tab stop position especially for tabular tasks. Position the cursor and choose tabs on the format main menu and specify the value for the tab stop in the interval by clicking on set button as below.

v                  Click on ok and input the values by pressing the tab key. Input the following information and find out the amount and grand total with the help of calculator.

MEMORY

Many types of memory devices are available for use in modern computer systems. As an embedded software engineer, you must be aware of the differences between them and understand how to use each type effectively. In our discussion, we will approach these devices from the software developer's perspective. Keep in mind that the development of these devices took several decades and that their underlying hardware differs significantly. The names of the memory types frequently reflect the historical nature of the development process and are often more confusing than insightful. Figure 1 classifies the memory devices we'll discuss as RAM, ROM, or a hybrid of the two.

Figure 1. Common memory types in embedded systems

Types of RAM

The RAM family includes two important memory devices: static RAM (SRAM) and dynamic RAM (DRAM). The primary difference between them is the lifetime of the data they store. SRAM retains its contents as long as electrical power is applied to the chip. If the power is turned off or lost temporarily, its contents will be lost forever. DRAM, on the other hand, has an extremely short data lifetime-typically about four milliseconds. This is true even when power is applied constantly.

In short, SRAM has all the properties of the memory you think of when you hear the word RAM. Compared to that, DRAM seems kind of useless. By itself, it is. However, a simple piece of hardware called a DRAM controller can be used to make DRAM behave more like SRAM. The job of the DRAM controller is to periodically refresh the data stored in the DRAM. By refreshing the data before it expires, the contents of memory can be kept alive for as long as they are needed. So DRAM is as useful as SRAM after all.

When deciding which type of RAM to use, a system designer must consider access time and cost. SRAM devices offer extremely fast access times (approximately four times faster than DRAM) but are much more expensive to produce. Generally, SRAM is used only where access speed is extremely important. A lower cost-per-byte makes DRAM attractive whenever large amounts of RAM are required. Many embedded systems include both types: a small block of SRAM (a few kilobytes) along a critical data path and a much larger block of DRAM (perhaps even Megabytes) for everything else.

Types of ROM

Memories in the ROM family are distinguished by the methods used to write new data to them (usually called programming), and the number of times they can be rewritten. This classification reflects the evolution of ROM devices from hardwired to programmable to erasable-and-programmable. A common feature of all these devices is their ability to retain data and programs forever, even during a power failure.

The very first ROMs were hardwired devices that contained a preprogrammed set of data or instructions. The contents of the ROM had to be specified before chip production, so the actual data could be used to arrange the transistors inside the chip. Hardwired memories are still used, though they are now called masked ROMs to distinguish them from other types of ROM. The primary advantage of a masked ROM is its low production cost. Unfortunately, the cost is low only when large quantities of the same ROM are required.

One step up from the masked ROM is the PROM (programmable ROM), which is purchased in an unprogrammed state. If you were to look at the contents of an unprogrammed PROM, you would see that the data is made up entirely of 1's. The process of writing your data to the PROM involves a special piece of equipment called a device programmer. The device programmer writes data to the device one word at a time by applying an electrical charge to the input pins of the chip. Once a PROM has been programmed in this way, its contents can never be changed. If the code or data stored in the PROM must be changed, the current device must be discarded. As a result, PROMs are also known as one-time programmable (OTP) devices.

An EPROM (erasable-and-programmable ROM) is programmed in exactly the same manner as a PROM. However, EPROMs can be erased and reprogrammed repeatedly. To erase an EPROM, you simply expose the device to a strong source of ultraviolet light. (A window in the top of the device allows the light to reach the silicon.) By doing this, you essentially reset the entire chip to its initial--unprogrammed--state. Though more expensive than PROMs, their ability to be reprogrammed makes EPROMs an essential part of the software development and testing process.

Hybrids

As memory technology has matured in recent years, the line between RAM and ROM has blurred. Now, several types of memory combine features of both. These devices do not belong to either group and can be collectively referred to as hybrid memory devices. Hybrid memories can be read and written as desired, like RAM, but maintain their contents without electrical power, just like ROM. Two of the hybrid devices, EEPROM and flash, are descendants of ROM devices. These are typically used to store code. The third hybrid, NVRAM, is a modified version of SRAM. NVRAM usually holds persistent data.

EEPROMs are electrically-erasable-and-programmable. Internally, they are similar to EPROMs, but the erase operation is accomplished electrically, rather than by exposure to ultraviolet light. Any byte within an EEPROM may be erased and rewritten. Once written, the new data will remain in the device forever--or at least until it is electrically erased. The primary tradeoff for this improved functionality is higher cost, though write cycles are also significantly longer than writes to a RAM. So you wouldn't want to use an EEPROM for your main system memory.

Flash memory combines the best features of the memory devices described thus far. Flash memory devices are high density, low cost, nonvolatile, fast (to read, but not to write), and electrically reprogrammable. These advantages are overwhelming and, as a direct result, the use of flash memory has increased dramatically in embedded systems. From a software viewpoint, flash and EEPROM technologies are very similar. The major difference is that flash devices can only be erased one sector at a time, not byte-by-byte. Typical sector sizes are in the range 256 bytes to 16KB. Despite this disadvantage, flash is much more popular than EEPROM and is rapidly displacing many of the ROM devices as well.

The third member of the hybrid memory class is NVRAM (non-volatile RAM). Nonvolatility is also a characteristic of the ROM and hybrid memories discussed previously. However, an NVRAM is physically very different from those devices. An NVRAM is usually just an SRAM with a battery backup. When the power is turned on, the NVRAM operates just like any other SRAM. When the power is turned off, the NVRAM draws just enough power from the battery to retain its data. NVRAM is fairly common in embedded systems. However, it is expensive--even more expensive than SRAM, because of the battery--so its applications are typically limited to the storage of a few hundred bytes of system-critical information that can't be stored in any better way.

Table 1 summarizes the features of each type of memory discussed here, but keep in mind that different memory types serve different purposes. Each memory type has its strengths and weaknesses. Side-by-side comparisons are not always effective.

Computer Booting:

Usually the process of starting your computer by switching on the power is called booting. But in actual term, the process of loading DOS system files into the memory of computer(RAM) from the disk (Floppy disk Or Hard Disk) is known as booting.

MS-DOS have three important system files that are loaded into the memory of computer are IO.SYS, MSDOS.SYS and COMMAND.COM. IO.SYS and MSDOS.SYS files are hidden files, which we can not see using simply DIR command.

Once The system files are loaded, DOS prompt appears on the screen and your computer is ready to receive and interpret the commands. If you are booting from the hard disk, your prompt may look like C:\, from the floppy disk A:\ in the screen.

TYPES OF BOOTING

Booting of computer can be done in two ways:

Cold Booting

Warm Booting

Cold Booting

When a computer is turned on, computer reads its RAM space and searches for the DOS system files from the disk drives (Floppy drive A:\  or Hard drive C:\). As soon as it finds the system files, those files will be loaded into computer’s memory from A:\ or C:\ drive, this kind of booting is called as Cold Booting.

So cols booting done when your compute is at OFF state, and you put on the power switch of the computer.

Warm Booting

If you are working with your computer and you wish to restart the compute, you simply press CTRL ALT and DEL keys at the same time, and your computer restarts again, searches DOS system files and loads into the computer’s memory. This is termed as Warm Booting. Sometime we press RESET button located nearby POWER button on the compute for warm booting.

COMPUTER NETWORK

   A computer network is an interconnection of various computer systems located at different places. In computer network two or more computers are linked together with a medium and data communication devices for the purpose of communicating data and sharing resources. The computer that provides resources to other computers on a network is known as server. In the network the individual computers, which access shared network resources, are known as workstations or nodes.

Computer Networks classified on the basis of geographical area in two broad categories:-

 1. Local Area Networks (LAN)

 2. Metropolitan Area Networks (MAN)

 3. Wide Area Networks (WAN)

EMAIL & INTERNET

Email

  E-mail stands for electronic mail. This is one of the most widely used features of Internet. Mails are regularly used today where with the help of postage stamp we can transfer mails anywhere in the world. With electronic mail the service is similar. But here data are transmitted through Internet and therefore within minutes the message reaches the destination may it be anywhere in the world. Therefore the mailing system is excessively fast and is being used widely for mail transfer

Internet

  The Internet is a network of networks. Millions of computers all over the world are connected through the Internet. Computer users on the Internet can contact one another anywhere in the world. If your computer is connected to the Internet, you can connect to millions of computers. You can gather information and distribute your data. It is very much similar to the telephone connection where you can talk with any person anywhere in the world.

In Internet a huge resource of information is accessible to people across the world. Information in every field starting from education, science, health, medicine, history, and geography to business, news, etc. can be retrieved through Internet. You can also download programs and software packages from anywhere in the world. Due to the tremendous information resources the Internet can provide, it is now indispensable to every organization.

Origin of Internet

In 1969 Department of Defense (DOD) of USA started a network called ARPANET (Advanced Research Projects Administration Network) with one computer at California and three at Utah. Later on other universities and R & D institutions were allowed to connect to the Network. APARNET quickly grew to encompass the entire American continent and became a huge success. Every university in the country wanted to become a part of ARPANET. So the network was broken into two smaller parts MILNET for managing military sites and ARPANET (smaller) for managing non-military sites. Around 1980, NSFNET (National Science Foundation Network) was created. With the advancement of modern communication facilities, other computers were also allowed to be linked up with any computer of NSFNET. By 1990 many computers were looking up to NSFNET giving birth to Internet.

How Internet functions

Internet is not a governmental organization. The ultimate authority of the Internet is the Internet Society. This is a voluntary membership organization whose purpose is to promote global information exchange. Internet has more than one million computers attached to it.