Operating System

Types of Operating System

Types of Operating System

Overlays

     One of the main limitations imposed on programmers in the early days of computing was the size of the computer's memory. If the program was larger than the available memory, it could not be loaded, which placed severe restrictions on program size. The obvious solution would be to increase the amount of memory available, but this would significantly increase the cost of the computer system. One way for a programmer to overcome these limitations was to use overlays. The programmer divided the program into a number of logical sections. A small portion of the program had to remain in memory at all times, but the remaining sections (or overlays) were loaded only when they were needed. The use of overlays allowed programmers to write programs that were much larger than physical memory, although responsibility for managing memory usage rested with the programmer rather than the operating system.

• The entire program and data of a process must be in the physical memory for the process to execute.
• The size of a process is limited to the size of physical memory.
• If a process is larger than the amount of memory, a technique called overlays can be used.
• Overlays is to keep in memory only those instructions and data that are needed at any given time.
• When other instructions are needed, they are loaded into space that was occupied previously by instructions that are no longer needed.
• Overlays are implemented by user, no special support needed from operating system, programming design of overlay structure is complex

Page Stealing

When this supply becomes low, OS uses page stealing to replenish it, that is, it takes a frame assigned to an active user and makes it available for other work. The decision to steal a particular page is based on the activity history of each page currently residing in a central storage frame. Pages that have not been active for a relatively long time are good candidates for page stealing.

Belady's Anamaly

This is a stage which occurs in FIFO page replacement algorithm, in which  a large number of page fault happens.

Preemptive scheduling

Task are usually assigned with priority at times it is necessary to run a certain task that has higher priority before another task although it is running  therefore the running task is interrupted for some time and resumes later when the priority task has finished its execution. This is called preemptive scheduling

E.g. Round-Robin

Non-Preemptive 

 In non preemptive scheduling a running task is executed till. it cannot be interrupted

E.g. FIFO 

Computer Memory

Memory

In computing, memory refers to the physical devices used to store programs (sequences of instructions) or data (e.g. program state information) on a temporary or permanent basis for use in a computer or other digital electronic device. The term primary memory is used for the information in physical systems which function at high-speed (i.e. RAM), as a distinction from secondary memory, which are physical devices for program and data storage which are slow to access but offer higher memory capacity. Primary memory stored on secondary memory is called "virtual memory".

Characteristics

Volatile memory

Volatile memory is a type of storage whose contents are erased when the system's power is turned off or interrupted. For example, RAM is volatile; meaning users will lose a document if they do not save their work to a non-volatile classification of memory, such as a hard drive, before shutting down the computer.

Non-volatile

Non-volatile is a term used to describe any memory or storage that is saved regardless if the power to the computer is on or off. The best example of non-volatile memory and storage is a computer hard drive, flash memory, and ROM. If data is stored on a hard drive, it will remain on that drive regardless if the power is interrupted, which is why it is the best place to store your data and documents. This is also how your computer keeps the time and other system settings even when the power is off.

Hamming Code

Data Error

Data error is term which occurs when we send data and it’s not received as we send.

Error Type

There are two type of error single bit and multiple bits (Burst)

Error detection and Correction

Error detection technique are user detect an error on the other hand error correction technique enable us to resolve an error. We can remove one, two and three bit error only because burst error may occur extremely.

Hamming code

Hamming code is a set of error-correction code s that can be used to detect and correct bit errors that can occur when computer data is moved or stored. Hamming code is named for R. W. Hamming of Bell Labs.

New Exam Pattern for UGC NET for Dec 2014

After UGC's failure, CBSE to conduct NET

NEW DELHI: Central Board of Secondary Education, the country's largest exam conducting body, is all set to add another test to its bouquet, the National Eligibility Test. The inclusion of the test from this year will make the board the biggest exam conducting body, with the number of CBSE candidates set to cross 65 lakh in a year.

After failing to conduct the test without hiccups, the University Grants Commission, with the HRD ministry's consent, has asked the CBSE to conduct the test. The decision was taken at the full commission meeting on Tuesday with near unanimity. The NET is conducted twice a year for grant of junior research fellowship and eligibility for assistant professor in institutions of higher learning.

Add an image to Google

To include a picture in Google search results, the first step is to add your image to a website along with a descriptive text for your image. While you can’t directly upload images into search results, searchable images that are posted on a website can be added to our search results.

                              

Step for upload your Image

• If you have a website then upload your image their 

september 1752 calendar missing days reason

In September 1752 the Julian calendar was replaced with the Gregorian calendar in Great Britain and its American colonies. The Julian calendar was 11 days behind the Gregorian calendar, so 14 September got to follow 2 September on the day of the change. The result was that between 3 and 13 September, absolutely nothing happened!

How to create automatic password using php

Password is widely used in computer as a security mechanism so we must make a password in such a manner which cannot be   guessable by any one. Mostly peoples make password pattern related to their life i.e. date of birth,city name,address or something like that which can be guess easily. So we must stop this practice, A strong password may be difficult to guess.

A strong password comprises special character, numeric, small and capital case character combination that restricts hacker to guess it. So I am representing coding that generate password automatically in strong form. You can use my coding if you want to generate password automatically.

<?php

                $msg="";

                 function makeRandomString ($length=8)

              {

                  $chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQ

                  RSTUVWXYZ0123456789!%,-:;@_{}~";

                  for ($i = 0, $makepass = '', $len = strlen($chars); $i < $length;

                  $i++) $makepass .= $chars[mt_rand(0, $len-1)];

                  return $makepass;

       }

                if(isset($_POST['pass']))

                                $msg=makeRandomString(10);

?>

<html>

<head>

<title>Untitled Document</title>

</head>

<body>

                <form action="<?php echo $_SERVER['PHP_SELF']?>" method="post" >

                <input type="submit" value="Get password" name="pass" />

        <h1><?php echo $msg;?></h1>

    </form>

</body>

</html>

Girfa Pics

Picture

A picture is a visual capture of an object. Pictures are created using another hardware device such as a digital camera or a scanner and not the computer. The picture of pictures shown here is a good example of a picture.

How to Add a Widget to Blogger

Widgets, also known as gadgets, are small tools or applications that can be added to a website or blog to enhance its content or functions, or to pull content and services from third-party websites. Widgets come in multiple forms, such as countdown tickers, photos, games, or interactive social media applications that allow you to chat. Some widgets in Blogger serve the purpose of enhancing your blog, such as listing your blog followers or allowing readers to subscribe to your blog content. Here are steps on how to add a widget to Blogger.

PHP Paging

I have made a website for flat selling. Many customer enquiries daily for flat booking by filling enquiry form. I have made an admin page which shows enquiry data of customer, everything was ok but when enquiry got increase then admin page data also increase so my client had to scroll very long that was not a good interface. So I decided to show enquiry table content page wise.

Thanks to limit clause used by MYSQL. You can use limit clause with select statement for limit the returns row from database, its takes two clause as a record number start and stop

I.e. Select * from Enquiry limit 0, 10

You can change limit clause argument for desire row, fist number for start and second one stand for stop retrieving row form table.

Click here to download full example

Core Java Programming

This post is for student who study java and they need many programs in their exam and test so I am trying to make some java programs which help them to make their work easy 

Question : Write a program which accept input of full path of a file and produce following output?

Input : C:/Users/Public/Pictures/SamplePictures/Desert.jpg

Output :

Extension : jpg

File Name : Desert

Path : C:/Users/Public/Pictures/SamplePictures

Solution :

import java.util.*;

public class Main

{

       public static void main(String[] args)

    {

        String str;

        Scanner sc=new Scanner(System.in);

        System.out.print("Enter your name>> ");

        str=sc.nextLine();

How to send email a form data using php

Form is a electronic way where organization gathered data from user through website. A website owner usually take details of esquires to his website using login provide by the website developer.

But we are familiar with email because it’s an era  of android word and every one configure email with mobile so sending form data in email as well as database is a good idea.

PHP provide a easy way to achieve this just take a look on flowing code and please don’t say thanks to me.

                    $to =' rajkumar9795@gmail.com';

                  $subject = 'Enquiry Data';

                  $message = "<h2>Welcome This is Enquiry for Now</h2><hr>Name : $_POST[name]<br>Gender :  $_POST[gen]<br>Course : $_POST[course]<br> Email : $_POST[email]<br>Mobile : $_POST[phone]<br>Query : $_POST[query]";

                 

                  $headers = 'From: bcmt@basantgroupofinstitution.org' . "\r\n" .

                                  'Reply-To: basantcollege.mt@gmail.com' . "\r\n" .

                                  'X-Mailer: PHP/' . phpversion().

'MIME-Version: 1.0' . "\r\n".

'Content-type: text/html; charset=iso-8859-1' . "\r\n";

                 

                            mail($to, $subject, $message, $headers);                                                

Window 7 Shortcut Keys

General Keyboard Shortcut
F1	Display Help
Ctrl+C	Copy the selected item
Ctrl+X	Cut the selected item
Ctrl+V	Paste the selected item
Ctrl+Z	Undo an action
Ctrl+Y	Redo an action
Delete	Delete the selected item and move it to the Recycle Bin
Shift+Delete	Delete the selected item without moving it to the Recycle Bin first
F2	Rename the selected item
Ctrl+Right Arrow	Move the cursor to the beginning of the next word
Ctrl+Left Arrow	Move the cursor to the beginning of the previous word
Ctrl+Down Arrow	Move the cursor to the beginning of the next paragraph
Ctrl+Up Arrow	Move the cursor to the beginning of the previous paragraph
Ctrl+Shift with an arrow key	Select a block of text

Window 7 Basic and Tutorial

The desktop (overview)

The desktop is the main screen area that you see after you turn on your computer and log on to Windows. Like the top of an actual desk, it serves as a surface for your work. When you open programs or folders, they appear on the desktop. You can also put things on the desktop, such as files and folders, and arrange them however you want.

The desktop is sometimes defined more broadly to include the taskbar. The taskbar sits at the bottom of your screen. It shows you which programs are running and allows you to switch between them. It also contains the Start button, which you can use to access programs, folders, and computer settings.

Working with desktop icons

Icons are small pictures that represent files, folders, programs, and other items. When you first start Windows, you'll see at least one icon on your desktop: The Recycle Bin (more on that later). Your computer manufacturer might have added other icons to the desktop. Some examples of desktop icons are shown below.

Examples of desktop icons

Double-clicking a desktop icon starts or opens the item it represents.

How to Find a Computer's MAC Address (Windows 7 and Vista)

A media access control address (MAC address) is a unique identifier assigned to network interfaces for communications on the physical network segment. MAC addresses are used as a network address for most IEEE 802 network technologies, including Ethernet. Logically, MAC addresses are used in the media access control protocol sublayer of the OSI reference model.
You can see your mac address by using following steps

    open start menu and Type ncpa.cpl into the search box and press ENTER as in image.

Right-click your Local Area Connection and select Status or just double click on Local Area Icon

Compare date in php

It’s really a horrible thing to work on date to being a programmer. If language is PHP then it’s too hard to achieve but don’t worry I have a best trick to solve it just take a look on following lines.

In PHP Date store in string format internally and time is store integer internally. You just have to change date into its equivalent time integer value and compare their integer as we work on number.

function compare_date($d1,$d2)

{

$date1=strtotime($d1);

$date2=strtotime($d2);

if($date1>$date2)

echo "First Date is greatest one";

else

echo "Second Date is greatest one";

}

I am using function for implement your logic you can work it where you want without using function 

First Things of Computer world

First Email Message

Ray Tomlinson

The first email was sent by Ray Tomlinson to himself in 1971. "The test messages were entirely forgettable. . . . Most likely the first message was QWERTYIOP or something similar," he said.

First Domain 

The first domain registered in 15-March 1985 named symbolics.com

Which is better between LCD screen and LED Screen

The differences between LED and LCD TV to a consumer as well as from the technical point of view are as follows:-
1. The viewing angle of LCD TV is less than that of LED TVs. LCD TVs are best viewed directly from in front and at the same plane as the screen i.e. a good view is not possible if viewed from the sides or from above or below the TV screen. LED TVs, on the other hand, has greater viewing angle.

2. LCD TVs can not be viewed under bright environment whereas LED TVs can be viewed even under direct sunlight. This is so because, the screen of LCD TVs made up of liquid crystals which changes color on passing current though it. Unlike LCD TVs, LED TV screens are made up of Light Emitting Diodes. Therefore, each tiny dot of light (pixel) on LED TV screen is like a light bulb and its glow is visible even under direct sunlight. For example, LCD TVs have the same screens as mobile phones and is not clearly visible under bright sunlight. You must have noticed that some mobile phones have light (a mobile torch).This torch is made up of an LED and thousands of such 'torch' form the LED TV screen.

Working With Document Versions

When you store a version of your document using the versions feature, you can access previous versions, delete any of the versions stored with your document, and recover document versions to a new file.

To view a version of your document
1. Select Versions… from the File menu
2. In the Versions dialog box, highlight the version you would like to open
3. Click Open

Captcha Using PHP

CAPTCHA  which stands for “Completely Automated Public Turing test to tell Computers and Humans Apart” is a type o f challenge-response test to ensure that the response is only generated by humans and not by a computer.

In simple words, CAPTCHA is the word verification test that you will come across the end of a sign-up form while signing up for Gmail or Yahoo account. The following image shows the typical samples of CAPTCHA.

You can make captcha using PHP. Here I am making number captcha which is achieved by an image. This image text is dynamically create by php and stored in session. A user can verify whether valid captcha has been entered or not.

Save this code in named captch.php

<?php 

session_start(); 

$text = rand(10000,99999); 

$_SESSION["vercode"] = $text; 

$height = 25; 

$width = 65;