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System Programs

What is system?

A system is a set of components that interact to be accomplish some common purpose.

i.e. human body, organisation.

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System ProgramsWhat is Operating System?

In computer an operating system is a program that acts as an intermediary between the user of a computer and the computer hardware.

In another way a mordan system is the collection of system programs.

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System ProgramsWhat is program?

A program is set of code that perform a specific process.

i.e. c program, visual basic program.

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System Programs

System programs provide a convenient environment for program development and execution.

Some of them are simply user interface to system calls ; others are considerably more complex.

Most users’ view of the operation system is defined by system programs, not the actual system calls.

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System ProgramsThe System program can be divided into seven parts:File manipulation Status informationFile modificationProgramming language supportProgram loading and executionCommunicationsApplication programs

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System Programs

System Programs Other User Applications

System Calls

Kernel

From OS’s view: system+user programs are all applications

Users (People)

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System CallsProgramming interface to the services

provided by the OSTypically written in a high-level language (C

or C++)Mostly accessed by programs via a high-

level Application Program Interface (API) rather than direct system call use

Three most common APIs are Win32 API for Windows, POSIX API for POSIX-based systems (including virtually all versions of UNIX, Linux, and Mac OS X), and Java API for the Java virtual machine (JVM)

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File ManagementWhat is File?

Collection of similar records call a file.It can be Treated as a single entity.It must Have name (file name).May restrict access.

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File ManagementFile management is one of the most

visible components of an operating system.

File management system consists of system utility programs that run as privileged applications.

Input to applications is by means of a file

Output is saved in a file for long-term storage

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File Management

File Management FunctionsIdentify and locate a selected file.Use a directory to describe the location of

all files plus their attributes.On a shared system describe user access

controlBlocking for access to filesAllocate files to free blocksManage free storage for available blocks

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File ManagementFile Operations

CreateDeleteOpenCloseReadWrite

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File ManagementTypical Operations On File

Retrieve_AllRetrieve_OneRetrieve_NextRetrieve_PreviousInsert_OneDelete_OneUpdate_OneRetrieve_Few

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Status informationSome programs ask the system for date,

time, amount of available, memory disk space, number of users or similar steatious information.

Typically, these programs format and print the output to the terminal or other output devices.

Some systems implement a registry - used to store and retrieve configuration information.

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File modification

Several text editors may also be available to create and modify the content of files stored on disk or tape.

Special commands to search contents of files or perform transformations of the text.

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Programming-language support

Compilers, assemblers, and interpreters for common programming languages (such as c, c++, Java, Visual Basic , and PERL) are often provided to the user with the operating system.

Some of these programs are now priced and provided seperately.

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Program loading and execution

Once a program is assembled or compiled , it must be loaded into memory to be executed.

The system may provided absolute loaders, relocatable loaders , linkage editors , and overlay loaders.

Debugging systems for either higher-level language are needed also.

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CommunicationsThese program provide the mechanism

for creating virtual connections among processes, users, and different computer systems.

Allow users to send messages to one another’s screens, browse web pages, send electronic-mail messages, log in remotely, transfer files from one machine to another.

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CommunicationsThere are two common models of

communication.1. Message-passing model.2. Shared-memory model.

1.Message-passing model :- In the message-passing model, information is

exchanged through an interprocess – communication facility provided by the operating system.

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Communications

Message-pasing Model is useful when smaller numbers of data need to be exchanged, because no conflicts need to be avoided.

It is also easier to implement than is shared memory for intercomputer communications.

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Communications

2.Shared-Memory model :-

In the Shared-memory model , process use map memory system calls to gain access to regions of memory owned by other memory process.

Shared-memory model allows maximum speed and convenience of communication, as it can be done at memory speeds when within a computer.

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Process AProcess A

Process BProcess B

KernelKernel

MM

MM

MM

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a) Message-Passing a) Message-Passing modelmodel

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Process AProcess A

Shared MemoryShared Memory

Process BProcess B

KernelKernel

1 1

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b) Shared-Memory Modelb) Shared-Memory Model23