Operating Systems Networks
Computer education means gaining basic knowledge and skills to operate computers in order to perform desired jobs. Computer Education not only involves basic knowledge about computer, computer education extends to various branches of study in various fields and sectors.
Operating Systems
The operating system is a complex collection of many programs concerned with keeping the hardware and software components of a computer system coordinated and functioning. It is like a shop keeper who keeps a shop in order by attending to customers, handling supplier deliveries, stocking the shelves, doing the bookkeeping, and so on.
The operating system is software; the same hardware can be used with many different operating systems (although only one at a time.) Sometimes the operating system on a computer becomes corrupted (perhaps because of a computer virus) and must be tediously re-installed. Until it is up and running again, other programs will not be available.
Starting a Program
When a computer is started up, the hardware will automatically load the operating system and start it running. This process is called booting. The reason for this odd term is that the operating system is itself involved in getting itself running---a process that is like someone "pulling themselves up by their bootstraps." Once the operating system is running, it is used to start up any other program.
Here is a (simplified) list of what happens when the user (you) starts up an application. Assume that the operating system (OS) is already running.
1. The user asks to run an application.
o This could be done by clicking on an icon, making a menu choice, or other means.
2. The OS determines the name of the application.
3. The OS finds the section of the hard disk where the application program and its data are stored.
4. The OS finds an unused section of main memory that is large enough for the application.
5. The OS makes a copy of the application and its data in that section of main memory.
o The software on the hard disk is unchanged; a copy of it has been made in main memory
6. The OS sets up resources for the application.
7. Finally, the OS starts the application running.
As the application runs, the OS is there in the background managing resources, doing input and output for the application, and keeping everything else running.
Networks
A computer network consists of two or more computers connected so that they can exchange data and programs. When a computer is a member of a network, the programs it runs and the data it uses can be on the hard disk of some other computer on the network. In business and industrial settings, most computers are on a network. The operating system that runs on a networked computer must manage its share of the network (along with managing all its other responsibilities.) The operating system is able to find programs and data that are stored on other network computers, and copy them into its own main memory.
In a local-area network only a few dozen computers are connected together, usually all located within the same building. Each computer has a network address that the other computers use to access it. Usually the computers share a printer. There may be an especially powerful computer called a server whose hard disk holds all the application programs and data that the other computers are expected to need.
Each computer in a network has a network interface card in its systems unit. This is an input/output device that sends and receives data over cables. The network interface cards of computers on a network are connected together with cables.
Wide-Area Networks
Large organizations need to connect many more computers than can be handled with a local area network. A wide-area network can connect thousands of computers together over great distances. The long distance connections are made by using fiber optic lines, telephone lines, microwave communications, and satellite communications. Each computer in the network has a network address (as with local-area networks) to uniquely identify it.
Wide-area networks use a variety of special hardware to manage the flow of data. When two computers share data, this hardware makes it appear that the two computers are connected together directly. In reality, there may be dozens of network devices between the two computers.
All these devices use the same method for dealing with data. Without a common method of dealing with data, a large network would become a hopeless muddle. An agreement about how to represent and transmit data over a network is called a protocol. Usually large networks use a protocol called TCP/IP (for transmission control protocol/internet protocol.)
The Internet consists of many wide-area networks that have been connected together to form one huge worldwide network. Even on this huge network, each computer must have a unique network address, much like each telephone in the world has a unique telephone number (if you include the country code and area code.)
World Wide Web
Remember that important idea (discussed several pages back):
Fundamental Idea: Both programs and data are saved in computer memory in the same way. The electronics of computer memory (both main memory and secondary memory) make no distinction between programs and data.
Communications equipment makes no distinction between programs and data, either. It is all information as far as it is concerned, and all information is transmitted the same way. The Internet is like a worldwide package delivery service. It is concerned with moving packages from one address to another, without concern about what is in the packages.
The Internet provides the hardware and the information transmission protocols for the World-Wide Web. Data intended for the Web is transmitted over the Internet just like any data. What makes Web data special is that it is intended for Web browsers (such as the one you are probably looking at.) A browser is a program that can read Web pages and display them in a nicely formatted way.
A Web page is a package of data that contains information on how it is to be displayed on a monitor. This information is given using a language called Hypertext Markup Language (HTML). If you want to see an example of what this looks like, left-click on View in your browser, then left-click on Page Source. After you are done viewing, click on the close button in the upper right corner (the button marked with X
Hyperlinks
One Web page is connected to another with a hyperlink. If you have been reading these notes over the Web, you have been linking between Web pages by using hyperlinks.
A web browser (such as Netscape Navigator) usually displays a hyperlink in a distinguishing color (usually blue.) When you click on it, the browser asks the operating system of the computer to get a particular Web page from another computer connected to the Internet. The Web page to get is specified with a uniform resource locator URL. A URL specifies both the computer (among all the Internet computers in the world) and the exact Web page on that computer.
End of the Chapter
We have ended this general overview of computer systems. At this point, you should have an idea of what computer systems are all about. But you will likely be uncertain about quite a few things. The following chapters will clarify some topics, and others will remain mystifying until later courses. For now, you may wish to review the following. Click on a blue subject that interests you to go to where it was discussed.
· Major hardware components of a computer system
The next chapter will discuss analog and binary signals and why binary signals are important in computer syste
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