Generation of operating systems

        A computer operating system is the software and/or firmware which manages the hardware of the computer and provides those resources, through an API, to application programs. By taking care of the hardware's needs and restrictions for the application program, the application program, and the application programmer, is freed from the additional work load and extra knowledge that is needed to deal with the hardware. This makes it easier to write application programs for that computer. It also makes it easier to keep a file system intact and working since all the changes to the file system go through the Operating system and are not done by each application programmer themselves

        The first computers didn't have operating systems, and could only run one program at a time. The first electronic computing circuits were little more than separate functions and didn't really need even a programming language to be tested. In about 1945 computers such as the Eniac were built that took up 4 square blocks of space and had about the same power as a 4 function calculator

By the 1950's the invention of the punch card machine made it easier to read in a small program, but all the operating of the system required was the pushing of a few buttons, one to load the cards into memory and another to run the program. They were designed to smooth the transition between jobs. Before the systems were developed, a great deal of time was lost between the completion of one job and the initiation of the next. This was the beginning of batch processing systems in which jobs were gathered in groups or batches.  Once a job was running, it had total control of the machine. As each job terminated (either normally or abnormally), control was returned to the operating system that "cleaned up after the job" and read in and initiated the next job.

In 1960 the operating systems were characterized by the development of shared systems with multiprogramming and beginnings of multiprocessing. In multiprogramming systems several user programs are in main storage at once and the processor is switched rapidly between the jobs. In multiprocessing systems, several processors are used on a single computer system to increase the processing power of the machine.
The IBM 360 was the first computer line to use small scale integrated circuits, and thus offered a major cut in price over earlier solid state machines.
Device independence began to appear. In first generation systems, a user wishing to write data on tape had to reference  a particular tape drive specifically. In this era, the user program specified only that a file was to be written  on a tape drive with a certain number of tracks and a certain density. The operating system located  an available tape drive with the desired characteristics and instructed the operator to mount a tape on that drive.
Timesharing systems were developed in which user could interface directly with the computer through typewriter like  terminals. Time sharing systems operate in an interactive or conversational mode with users. The user types a request to the computer, the computer processes the request as soon as it can (often within a second or less), and a response (if any) is typed on the user's terminal. Conversational computing made possible great strides in the program development process. A timesharing user could locate and correct errors in seconds or minutes, rather than suffering the delays, often hours or days, in batch processing environments.
Timesharing didn't become popular until late in the third generation when the hardware for protection mechanisms became widespread

In 1964 The IBM system/360 family of computers third generation computers was designed to be general-purpose systems. They were large, often ponderous, systems purporting to be all things to all people. The concept sold a lot of computers, but it took its toll. Users running particular applications that did not require this kind of power played heavily in increased run-time over head, learning time, debugging time, maintenance, etc.
Third generation operating systems were multitude systems. Some of them simultaneously supported batch processing, time sharing, real-time processing, and multiprocessing. They were  large and expensive. Nothing like them had ever  been constructed before, and many of the development efforts finished well over budget and long after scheduled completion.
These systems introduced to computer environments a greater complexity to which users were, at first, unaccustomed. The systems interposed a software layer between the user and the hardware. This software  layer was often so thick that a user lost sight of the hardware and so only the view created by the software. To get one of these systems to perform the simplest useful task, users had to become familiar with complex job control languages to specify the jobs their resource requirements. Third generation operating systems represented  a great step forward, but a painful one for many users.

     Fourth generation systems are the current state of the art. Many designers and users are still smarting from their experiences with third generation operating systems and are careful before getting involved with complex operating systems.
With the widespread use of computer networking and on-line processing, user gain access to networks of geographically dispersed computers through various types of terminals. The microprocessor has made possible the development of the personal computer, one of the most important developments of social consequence  in the last several decades. Now many users have dedicated computer systems available for their own use at any time of the day or night. Computer  power that cost hundreds of thousands of dollars in the early 1960s is now available for less than a thousand dollars.
Personal computers are often equipped with data communications interface, and also serve as terminals. The user of a fourth generation system is no longer confined to communicating with a single computer in a timeshared mode. Rather the user may communicate with geographically dispersed systems. Security problems have increased greatly with information now passing over various types of vulnerable communications lines. Encryption is receiving much attention it has become necessary to encode highly proprietary or personal data so that, even if the data is compromised, it  is of no use to anyone other than the  intended receivers.
     The percentage of the population with access to computers in the 1980s is far greater than ever before and growing rapidly. It is common to hear the term user friendly denoting systems that give users of average intelligence easy access to computer power. The highly symbolic, mnemonic, acronym-oriented user environments of the 1960s and 1970s are being replaced in the 1980s by menu-driven systems that guide the user through various options expressed in simple English.
The concept of virtual machines has become widely used. The user is no longer concerned with the physical details of the computer systems (or network) being accessed. Instead the user sees a view called a virtual machine created by the operating system. Today's user is more concerned with accomplishing work with a computer. And is generally not interested in the internal functioning of the machine.
Database systems have gained central importance. Ours is an information-oriented society, and the job of database systems is to make information conveniently accessible in a controlled fashion to those who have a right to access it. Thousands of on-line database have become available for access via terminals over communications networks.
The concept of distributed data processing has become firmly entrenched. We are now concerned with bringing the computer power to the site at which it is needed, rather than bringing the data to some central computer installation for processing.

latest crush

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Having Fan

History of operating systems

History of Operating Systems.

The earliest computers were mainframes that lacked any form of operating system. . Each user had sole use of the machine for a scheduled period of time and would arrive at the computer with program and data, often on punched paper cards and magnetic or paper tape. The program would be loaded into the machine, and the machine would be set to work until the program completed or crashed. Programs could generally be debugged via a control panel using toggle switches and panel lights. Symbolic languages, assemblers, and compilers were developed for programmers to translate symbolic program-code into machine code that previously would have been hand-encoded. Later machines came with libraries of support code on punched cards or magnetic tape, which would be linked to the user's program to assist in operations such as input and output. This was the genesis of the modern-day operating system.
The true descendant of the early operating systems is what is now called the "kernel”
The first operating system used for real work was GM-NAA I/O, produced in 1956 by General Motors Research division for its IBM 704. The main function of GM-NAA I/O was to automatically execute a new program once the one that was being executed had finished (batch processing). It was formed of shared routines to the programs that provided common access to the input/output devices. Some version of the system was used in about forty 704 installations. Control Data Corporation developed the SCOPE operating system in the 1960s, for batch processing and later developed the MACE operating system for time sharing, which was the basis for the later Kronos. In cooperation with the University of Minnesota, the Kronos and later the NOS operating systems were developed during the 1970s, which supported simultaneous batch and timesharing use. Like many commercial timesharing systems, its interface was an extension of the DTSS time sharing system, one of the pioneering efforts in timesharing and programming languages. In the 1970s, UNIVAC produced the Real-Time Basic (RTB) system to support large-scale time sharing.


after a while by Judith

After a while you learn
the subtle difference between
holding a hand and chaining a soul
and you learn
that love doesn't mean leaning
and company doesn't always mean security.
And you begin to learn
that kisses aren't contracts
and presents aren't promises
and you begin to accept your defeats
with your head up and your eyes ahead
with the grace of woman,
not the grief of a child
and you learn
to build all your roads on today
because tomorrow's ground is
too uncertain for plans
and futures have a way of falling down
in mid-flight.
After a while you learn
that even sunshine burns
if you get too much
so you plant your own garden
and decorate your own soul
instead of waiting for someone
to bring you flowers.
And you learn that you really can endure
you really are strong
you really do have worth
and you learn
and you learn
with every goodbye, you learn...

Introduction to css style sheets

What You Should Already Know
Before you continue you should have a basic understanding of the following:
If you want to study these subjects first, find the tutorials on our Home page.

What is CSS?
  • CSS stands for Cascading Style Sheets
  • Styles define how to display HTML elements
  • Styles were added to HTML 4.0 to solve a problem
  • External Style Sheets can save a lot of work
  • External Style Sheets are stored in CSS files

CSS Demo
An HTML document can be displayed with different styles: See how it works

Styles Solved a Big Problem
HTML was never intended to contain tags for formatting a document.
HTML was intended to define the content of a document, like:
<h1>This is a heading</h1>
<p>This is a paragraph.</p>
When tags like <font>, and color attributes were added to the HTML 3.2 specification, it started a nightmare for web developers. Development of large web sites, where fonts and color information were added to every single page, became a long and expensive process.
To solve this problem, the World Wide Web Consortium (W3C) created CSS.
In HTML 4.0, all formatting could be removed from the HTML document, and stored in a separate CSS file.
All browsers support CSS today.

CSS Saves a Lot of Work!
CSS defines HOW HTML elements are to be displayed.
Styles are normally saved in external .css files. External style sheets enable you to change the appearance and layout of all the pages in a Web site, just by editing one single file!

CSS Syntax

A CSS rule has two main parts: a selector, and one or more declarations:
The selector is normally the HTML element you want to style.
Each declaration consists of a property and a value.
The property is the style attribute you want to change. Each property has a value.

CSS Example

A CSS declaration always ends with a semicolon, and declaration groups are surrounded by curly brackets:
p {color:red;text-align:center;}
To make the CSS more readable, you can put one declaration on each line, like this:



CSS Comments

Comments are used to explain your code, and may help you when you edit the source code at a later date. Comments are ignored by browsers.
A CSS comment begins with "/*", and ends with "*/", like this:
/*This is a comment*/
/*This is another comment*/

Three Ways to Insert CSS

There are three ways of inserting a style sheet:
  • External style sheet
  • Internal style sheet
  • Inline style

External Style Sheet

An external style sheet is ideal when the style is applied to many pages. With an external style sheet, you can change the look of an entire Web site by changing one file. Each page must link to the style sheet using the <link> tag. The <link> tag goes inside the head section:
<link rel="stylesheet" type="text/css" href="mystyle.css" />
An external style sheet can be written in any text editor. The file should not contain any html tags. Your style sheet should be saved with a .css extension. An example of a style sheet file is shown below:
hr {color:sienna;}
p {margin-left:20px;}
body {background-image:url("images/back40.gif");}
RemarkDo not leave spaces between the property value and the units! "margin-left:20 px" (instead of "margin-left:20px") will work in IE, but not in Firefox or Opera.

Internal Style Sheet

An internal style sheet should be used when a single document has a unique style. You define internal styles in the head section of an HTML page, by using the <style> tag, like this:
<style type="text/css">
hr {color:sienna;}
p {margin-left:20px;}
body {background-image:url("images/back40.gif");}

Inline Styles

An inline style loses many of the advantages of style sheets by mixing content with presentation. Use this method sparingly!
To use inline styles you use the style attribute in the relevant tag. The style attribute can contain any CSS property. The example shows how to change the color and the left margin of a paragraph:
<p style="color:sienna;margin-left:20px">This is a paragraph.</p>

Multiple Style Sheets

If some properties have been set for the same selector in different style sheets, the values will be inherited from the more specific style sheet.
For example, an external style sheet has these properties for the h3 selector:
And an internal style sheet has these properties for the h3 selector:
If the page with the internal style sheet also links to the external style sheet the properties for h3 will be:
The color is inherited from the external style sheet and the text-alignment and the font-size is replaced by the internal style sheet.

Multiple Styles Will Cascade into One

Styles can be specified:
  • inside an HTML element
  • inside the head section of an HTML page
  • in an external CSS file
Tip: Even multiple external style sheets can be referenced inside a single HTML document.

Cascading order

What style will be used when there is more than one style specified for an HTML element?
Generally speaking we can say that all the styles will "cascade" into a new "virtual" style sheet by the following rules, where number four has the highest priority:
  1. Browser default
  2. External style sheet
  3. Internal style sheet (in the head section)
  4. Inline style (inside an HTML element)
So, an inline style (inside an HTML element) has the highest priority, which means that it will override a style defined inside the <head> tag, or in an external style sheet, or in a browser (a default value).
RemarkNote: If the link to the external style sheet is placed after the internal style sheet in HTML <head>, the external style sheet will override the internal style sheet!

CSS Id and Class

The id and class Selectors

In addition to setting a style for a HTML element, CSS allows you to specify your own selectors called "id" and "class".

The id Selector

The id selector is used to specify a style for a single, unique element.
The id selector uses the id attribute of the HTML element, and is defined with a "#".
The style rule below will be applied to the element with id="para1":


RemarkDo NOT start an ID name with a number! It will not work in Mozilla/Firefox.

The class Selector

The class selector is used to specify a style for a group of elements. Unlike the id selector, the class selector is most often used on several elements.
This allows you to set a particular style for many HTML elements with the same class.
The class selector uses the HTML class attribute, and is defined with a "."
In the example below, all HTML elements with class="center" will be center-aligned:


.center {text-align:center;}
You can also specify that only specific HTML elements should be affected by a class.
In the example below, all p elements with class="center" will be center-aligned:

Example {text-align:center;}
RemarkDo NOT start a class name with a number! This is only supported in Internet Explorer.


CSS Background

CSS background properties are used to define the background effects of an element.
CSS properties used for background effects:
  • background-color
  • background-image
  • background-repeat
  • background-attachment
  • background-position

Background Color

The background-color property specifies the background color of an element.
The background color of a page is defined in the body selector:


body {background-color:#b0c4de;}
With CSS, a color is most often specified by:
  • a HEX value - like "#ff0000"
  • an RGB value - like "rgb(255,0,0)"
  • a color name - like "red"
Look at CSS Color Values for a complete list of possible color values.
In the example below, the h1, p, and div elements have different background colors:


h1 {background-color:#6495ed;}
p {background-color:#e0ffff;}
div {background-color:#b0c4de;}

Background Image

The background-image property specifies an image to use as the background of an element.
By default, the image is repeated so it covers the entire element.
The background image for a page can be set like this:


body {background-image:url('paper.gif');}
Below is an example of a bad combination of text and background image. The text is almost not readable:


body {background-image:url('bgdesert.jpg');}

Background Image - Repeat Horizontally or Vertically

By default, the background-image property repeats an image both horizontally and vertically.
Some images should be repeated only horizontally or vertically, or they will look strange, like this: 


If the image is repeated only horizontally (repeat-x), the background will look better:



Background Image - Set position and no-repeat

RemarkWhen using a background image, use an image that does not disturb the text.
Showing the image only once is specified by the background-repeat property:


In the example above, the background image is shown in the same place as the text. We want to change the position of the image, so that it does not disturb the text too much.
The position of the image is specified by the background-position property:


background-position:right top;

Background - Shorthand property

As you can see from the examples above, there are many properties to consider when dealing with backgrounds.
To shorten the code, it is also possible to specify all the properties in one single property. This is called a shorthand property.
The shorthand property for background is simply "background":


body {background:#ffffff url('img_tree.png') no-repeat right top;}
When using the shorthand property the order of the property values are:
  • background-color
  • background-image
  • background-repeat
  • background-attachment
  • background-position
It does not matter if one of the property values is missing, as long as the ones that are present are in this order.
This example uses more advanced CSS. Take a look: Advanced example


More Examples

How to set a fixed background image
This example demonstrates how to set a fixed background image. The image will not scroll with the rest of the page.

All CSS Background Properties

Sets all the background properties in one declaration
Sets whether a background image is fixed or scrolls with the rest of the page
Sets the background color of an element
Sets the background image for an element
Sets the starting position of a background image
Sets how a background image will be repeated

Text Color
The color property is used to set the color of the text.
With CSS, a color is most often specified by:
  • a HEX value - like "#ff0000"
  • an RGB value - like "rgb(255,0,0)"
  • a color name - like "red"
Look at CSS Color Values for a complete list of possible color values.
The default color for a page is defined in the body selector.
body {color:blue;}
h1 {color:#00ff00;}
h2 {color:rgb(255,0,0);}
RemarkFor W3C compliant CSS: If you define the color property, you must also define the background-color property.

Text Alignment
The text-align property is used to set the horizontal alignment of a text.
Text can be centered, or aligned to the left or right, or justified.
When text-align is set to "justify", each line is stretched so that every line has equal width, and the left and right margins are straight (like in magazines and newspapers).
h1 {text-align:center;} {text-align:right;}
p.main {text-align:justify;}

Text Decoration
The text-decoration property is used to set or remove decorations from text.
The text-decoration property is mostly used to remove underlines from links for design purposes:
a {text-decoration:none;}
It can also be used to decorate text:
h1 {text-decoration:overline;}
h2 {text-decoration:line-through;}
h3 {text-decoration:underline;}
h4 {text-decoration:blink;}
RemarkIt is not recommended to underline text that is not a link, as this often confuses users.

Text Transformation
The text-transform property is used to specify uppercase and lowercase letters in a text.
It can be used to turn everything into uppercase or lowercase letters, or capitalize the first letter of each word.
p.uppercase {text-transform:uppercase;}
p.lowercase {text-transform:lowercase;}
p.capitalize {text-transform:capitalize;}

Text Indentation
The text-indentation property is used to specify the indentation of the first line of a text.
p {text-indent:50px;}

More Examples
Specify the space between characters
This example demonstrates how to increase or decrease the space between characters.
Specify the space between lines
This example demonstrates how to specify the space between the lines in a paragraph.
Set the text direction of an element
This example demonstrates how to change the text direction of an element.
Increase the white space between words
This example demonstrates how to increase the white space between words in a paragraph.
Disable text wrapping inside an element
This example demonstrates how to disable text wrapping inside an element.
Vertical alignment of an image
This example demonstrates how to set the vertical align of an image in a text.

All CSS Text Properties
Sets the color of text
Specifies the text direction/writing direction
Increases or decreases the space between characters in a text
Sets the line height
Specifies the horizontal alignment of text
Specifies the decoration added to text
Specifies the indentation of the first line in a text-block
Specifies the shadow effect added to text
Controls the capitalization of text

Sets the vertical alignment of an element
Specifies how white-space inside an element is handled
Increases or decreases the space between words in a text

CSS Font

CSS font properties define the font family, boldness, size, and the style of a text.

Difference Between Serif and Sans-serif Fonts

Serif vs. Sans-serif
RemarkOn computer screens, sans-serif fonts are considered easier to read than serif fonts.

CSS Font Families

In CSS, there are two types of font family names:
  • generic family - a group of font families with a similar look (like "Serif" or "Monospace")
  • font family - a specific font family (like "Times New Roman" or "Arial")
Generic family
Font family
Times New Roman
Serif fonts have small lines at the ends on some characters
"Sans" means without - these fonts do not have the lines at the ends of characters
Courier New
Lucida Console
All monospace characters have the same width

Font Family

The font family of a text is set with the font-family property.
The font-family property should hold several font names as a "fallback" system. If the browser does not support the first font, it tries the next font.
Start with the font you want, and end with a generic family, to let the browser pick a similar font in the generic family, if no other fonts are available.
Note: If the name of a font family is more than one word, it must be in quotation marks, like font-family: "Times New Roman".
More than one font family is specified in a comma-separated list:


p{font-family:"Times New Roman", Times, serif;}
For more commonly used font combinations, look at our Web Safe Font Combinations.

Font Style

The font-style property is mostly used to specify italic text.
This property has three values:
  • normal - The text is shown normally
  • italic - The text is shown in italics
  • oblique - The text is "leaning" (oblique is very similar to italic, but less supported)


p.normal {font-style:normal;}
p.italic {font-style:italic;}
p.oblique {font-style:oblique;}

Font Size

The font-size property sets the size of the text.
Being able to manage the text size is important in web design. However, you should not use font size adjustments to make paragraphs look like headings, or headings look like paragraphs.
Always use the proper HTML tags, like <h1> - <h6> for headings and <p> for paragraphs.
The font-size value can be an absolute, or relative size.
Absolute size:
  • Sets the text to a specified size
  • Does not allow a user to change the text size in all browsers (bad for accessibility reasons)
  • Absolute size is useful when the physical size of the output is known
Relative size:
  • Sets the size relative to surrounding elements
  • Allows a user to change the text size in browsers
RemarkIf you do not specify a font size, the default size for normal text, like paragraphs, is 16px (16px=1em).

Set Font Size With Pixels

Setting the text size with pixels, gives you full control over the text size:


h1 {font-size:40px;}
h2 {font-size:30px;}
p {font-size:14px;}
The example above allows Internet Explorer 9, Firefox, Chrome, Opera, and Safari to resize the text.
Note: The example above does not work in IE, prior version 9.
The text can be resized in all browsers using the zoom tool (however, this resizes the entire page, not just the text).

Set Font Size With Em

To avoid the resizing problem with older versions of Internet Explorer, many developers use em instead of pixels.
The em size unit is recommended by the W3C.
1em is equal to the current font size. The default text size in browsers is 16px. So, the default size of 1em is 16px.
The size can be calculated from pixels to em using this formula: pixels/16=em


h1 {font-size:2.5em;} /* 40px/16=2.5em */
h2 {font-size:1.875em;} /* 30px/16=1.875em */
p {font-size:0.875em;} /* 14px/16=0.875em */
In the example above, the text size in em is the same as the previous example in pixels. However, with the em size, it is possible to adjust the text size in all browsers.
Unfortunately, there is still a problem with older versions of IE. The text becomes larger than it should when made larger, and smaller than it should when made smaller.

Use a Combination of Percent and Em

The solution that works in all browsers, is to set a default font-size in percent for the <body> element:


body {font-size:100%;}
h1 {font-size:2.5em;}
h2 {font-size:1.875em;}
p {font-size:0.875em;}
Our code now works great! It shows the same text size in all browsers, and allows all browsers to zoom or resize the text!


More Examples

Set the boldness of the font
This example demonstrates how to set the boldness of a font.
Set the variant of the font
This example demonstrates how to set the variant of a font.
All the font properties in one declaration
This example demonstrates how to use the shorthand property for setting all of the font properties in one declaration.

All CSS Font Properties

Sets all the font properties in one declaration
Specifies the font family for text
Specifies the font size of text
Specifies the font style for text
Specifies whether or not a text should be displayed in a small-caps font
Specifies the weight of a font