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Speakers. Speakers are used to play sound. They may be built into the system unit or connected with cables. Speakers allow you to listen to music and hear sound effects from your computer (Figure 13).

Figure 13 - Computer speakers

Modem. To connect your computer to the Internet, you need a modem. A modem is a device that sends and receives computer information over a telephone line or high-speed cable. Modems are sometimes built into the system unit, but higher-speed modems are usually separate components (Figure 14).

Figure 14 - Cable modem

Figure 15 – Developing technologies

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  Computer nowadays.
  

The primary need for the OS arises from the fact that user needs to be provided with services and OS ought to facilitate the provisioning of these services. The central part of a computer system is a processing engine called CPU. A system should make it possible for a user’s application to use the processing unit. A user application would need to store information. The OS makes memory available to an application when required (Figure 16). Similarly, user applications need use of input facility to communicate with the application. This is often in the form of a key board, or a mouse or even a joy stick (if the application is a game for instance).

Figure 16 – Parts of computer

Let us consider few applications.

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  Document Design.
  
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  Accounting.
  
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  E-mail.
  
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  Image processing Operating Systems/Introduction to Operating System Lecture Notes.
  
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  Games.
  

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  Processing information.
  
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  Storage of Information.
  
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  Mechanism to inputting information.
  
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  Provision for outputting information.
  
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  These service facilities are provided by an operating system regardless of the nature of application.
  

From the user point of view the primary consideration is always the convenience. It should be easy to use an application. In launching an application, it helps to have an icon which gives a clue which application it is. We have seen some helpful clues for launching a browser, e-mail or even a document preparation application. In other words, the human computer interface which helps to identify an application and its launch is very useful (Figure 17).

Figure 17 – Working scheme

Also, OS needs to ensure that system resources are utilized efficiently. For instance, there may be many service requests on a Web server. Each user request need to be serviced. Similarly, there may be many programs residing in the main memory. The system need to determine which programs are active and which need to await some form of input or output. Those that need to wait can be suspended temporarily from engaging the processor. This strategy alone enhances the processor throughput. In other words, it is important for an operating system to have a control policy and algorithm to allocate the system resources.

It would be worthwhile to trace some developments that have happened in the last four to five decades. In the 1960s, the common form of computing facility was a mainframe computer system. The mainframe computer system would be normally housed in a computer center with a controlled environment which was usually an air conditioned area with a clean room like facility. The users used to bring in a deck of punched cards which encoded the list of program instructions.

The mode of operation was as follows:

- User would prepare a program as a deck of punched cards.

- The header cards in the deck were the “job control” cards which would indicate which compiler was to be used (like Fortran / Cobol compilers).

- The deck of cards would be handed in to an operator who would collect such jobs from various users.

- The operators would invariably group the submitted jobs as Fortran jobs, Cobol jobs etc. In addition, these were classified as “long jobs” that required considerable processing time or short jobs which required a short and limited computational time.

Each set of jobs was considered as a batch and the processing would be done for a batch.

Like for instance there may be a batch of short Fortran jobs. The output for each job would be separated and turned over to users in a collection area. This scenario clearly shows that there was no interactivity. Users had no direct control. Also, at any one time only one program would engage the processor. This meant that if there was any input or output in between processing then the processor would wait idling till such time that the I/O is completed. This meant that processor would idling most of the time as processor speeds were orders of magnitude higher than the input or output or even memory units.

Figure 18 - Chart