Operating system



Operating system Unit 1 !!

1. What is an operating system ? Highlight its important features and working components. .
	An operating system (OS) is system software that manages computer hardware and software resources and provides common services for computer programs.

An operating system (OS) is the program that, after being initially loaded into the computer by a boot program, manages all the other programs in a computer. The other programs are called applications or application programs. The application programs make use of the operating system by making requests for services through a defined application program interface (API). In addition, users can interact directly with the operating system through a user interface such as a command line or a graphical user interface (GUI).
An operating system performs these services for applications:

1. In a multitasking operating system where multiple programs can be running at the same time, the operating system determines which applications should run in what order and how much time should be allowed for each application before giving another application a turn.
2. It manages the sharing of internal memory among multiple applications.
3. It handles input and output to and from attached hardware devices, such as hard disks, printers, and dial-up ports.
4. It sends messages to each application or interactive user (or to a system operator) about the status of operation and any errors that may have occurred.
5. It can offload the management of what are called batch jobs (for example, printing) so that the initiating application is freed from this work.
6. On computers that can provide parallel processing, an operating system can manage how to divide the program so that it runs on more than one processor at a time.
An Operating System can roughly be divided into four components :
1. The Hardware
2. The Application Programs
3. The Operating System
4. The Users

The application programs such as word processors/ spreadsheets/ compilers, and Web browsers-define the ways in which these resources are used to solve users computing problems. The operating system controls the hardware and coordinates its use among the various application programs for the various users.




2. Write short notes on storage structure of a system. support your answers with diagrams if required.
	Storage Structure

The Storage Structure of a computer system defines the storing capacity. There are various types of storing structure and different capacity are available for storing files and different data. Secondary storage devices are those devices whose memory is non volatile, meaning, the stored data will be intact even if the system is turned off.

Functions of storage structure of a system are as follows :
1. Receives data and instructions for processing from input devices.
2. It holds the immediate results
3. It stores the final results before the results are released to an output device.
4. It is used to store files and documents.
5. It helps in loading the operating system.
6. It is used to store data permanently.
There are mainly two types of storages in the system : -
1. Primary Memory ( Main Memory )
2. Secondary Storage

Memory is a storage capacity os any device that is used to store data , data variable, files and documents.
MAIM MEMORY
A unit that communiates directly to the CPU is called the main memory.CPU takes the instruction from the main memory.All the programs and data that is currently being used by the CPU is kept in main memory

Features :

1. Fast
2. Expensive
3. Low Capacity
4. Works directly with the processor.

Broadly there are two types of main memory

1. RAM ( Random Access Memory )
2. ROM ( Read Only Memory .

1. RAM ( Random Access Memory ) : RAM is a volatile memory that if the power is switched off, the information stored in it iss erased. immidiately.It is also known as temperory memory.In this memory, information stoted can be accessed directly or randomly. RAM is further classified in Dynamic RAM and Static RAM.

2. ROM ( Read Only Memory ) : performs only read operations. In ROM write operation is not permitted. ROM is used to store Basic Input Output Operations ( BIOS) that are required when the computer is first turne on. ROMs are non volatile in nature and need not to be stored or loaded in a secondary memory. It cannot be altered or fresh or new data cannot be written into ROM. ROMs are used for applications in which it is known that information never needs to be altered.

PROM ( Programable Read Only Memory ) is a type of ROM that can be programed only once. PROM is a way of allowing a user to tailor a microcode program using a special machine called a PROM programmer . This machine supplies an electrical current to specific cells in the ROM that effectively blows a fuse in them. The process is known as burning the PROM .

EPROM (erasable programmable read-only memory) is programmable read-only memory (programmable ROM) that can be erased and re-used.The content can be erased when ever required. It needs ultra voilet rays for erasing and programming and hence it is known as Ultra Voilet Programable Read Only Memory ( UPROM ).

EAROM ( Electrically Alterable Read Only Memory ) : It does not require UV light to erase the contents but uses small charge of electricity. A form of semiconductor memory in which it is possible to change the contents of selected memory locations by applying suitable electric signals. Normally these changes are infrequent.Information stored in this memory can be restained for many years without any power supply.

EEPROM ( Electrically Erasable Programmable Read Only Memory ) : In EEPROM the contents can be erased by specific software. These are commonly used to store BIOS ( Basic Input Output System ) and are non volatile memory. The contents of these memories can be changed easily. These are high cost memory in which write operation is faster than read operation.

Secondary Memory
This memory is permanent in nature and capable of storing large volume of data.Secondary memory is where programs and data are kept on a long-term basis. For eg. Hard Disk, Magnetic tapes, Magnetic Disks and so on. These are non volatile memories are are slower than main memory.

Features :
1. Slow
2. Cheap
3. Large Capacity
4. Not connected directly with the processor.

Cache Memory
Cache Memory was introduced to compensate the speed gap between the CPU and the Main Memry. It is hidden memory that is user cannot see or address it. The purpose of cache is to speed up memory access by soring recently used chunks of memory. It is very expensive. Cache memory, also called CPU memory, is high-speed static random access memory (SRAM) that a computer microprocessor can access more quickly than it can access regular random access memory (RAM).It is a very high speed memory that is placed between the CPU and main memory, to operate at the speed of the CPU. It is used to reduce the average time to access data from the main memory. The cache is a smaller and faster memory which stores copies of the data from frequently used main memory locations.




3. Write short notes on computer system architecture elaborating multiprocessors and its functions. also elaborate clustered systems
	A computer system may be organised in a number of different ways, which we can categorise roughly according to the number of general purpose processors used.

1. Single Processor Systems : On a single processor system there is one main CPU capable of executing a general purpose execution set, including instructions from user processes. Almost all systems have special purpose processors as well. They may come in device specific processors such as disk, keyboards and graphics controller.

2. Multiprocessor Systems : also known as parallel systems or tightly coupled systems. Such systems have two or more processors in close communication, sharing the computer bus , the clock , memory and other peripheral devices.

Multiprocessors have three main advantages :

1. Increased Throughput : Throughput is measure of units of information a system process in a given amount of time. It is applied broadly to systems ranging from various aspects of computer and network systems to organisations.

2. Economy of Scale : Multiprocessor systems can cost less than equivalent multiple single processor systems, because they can share peripherals, mass storage and power supplies. If several programs operate on same set of data , it is cheaper to store those data on one disk and to have all the processors share them than to have many computer with local disks.

3. Increased Reliability : If the functions can be distributed properly among several processors, than the failure of one processor will not halt the system, only slow it down.
The multiprocessor systems in use today are of two types :

1. Asymmetric Multiprocessing
2. Symmetric Multiprocessing

1. Asymmetric Multiprocessing : In which each processor is assigned a specific task. A master processor controls the system, the other processors either look to the master for instruction or have predefined task.

1. Symmetric Multiprocessing ( SMP ) : In which each processor performs all tasks within the operating system. SMP means all processor are peers, no master slave relationship exists between processors. For eg. Solaris, a commercial version of UNIX designed by Sun Microsystems.

CLUSTERED SYSTEMS

It is a multiple CPU system. Clustered systems gather together multiple CPUs to accomplish a computational work. Clustered systems share storage and are closely linked via Local Area Network ( LAN).Clustered System is used to provide high availability service that is service will continue even one more systems in the cluster fail. High availability is generally obtained by adding level of redundancy in the system. A layer of cluster software runs on the cluster nodes. Each node can monitor one or more of others in LAN. If the monitored machine fails , the monitoring machine can take ownership of its storage and restart the applications that were running on the failed machine.




4. What is a multimedia system? Specify its various characteristics.
	A Multimedia System is a system capable of processing multimedia data and applications. It is characterized by the processing, storage, generation, manipulation
and rendition of Multimedia information. 

Characteristics of a Multimedia Systems
A Multimedia systems has four basic characteristics:
1. Multimedia systems must be computer
controlled.
2.  Multimedia systems are integrated.
3. The information they handle must be
represented digitally.
4. The interface to the final presentation of media
is usually interactive.




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