 PROCESS MANAGEMENT  A process is a program in execution: (A program is passive, a process active.)  A process has resources (CPU time, files) and attributes that must be managed. Management of processes includes:  Process Scheduling - priority, time management.  Creation/Termination  Reason for Terminating:  User logs off  Process executes a service request to terminate Process  Error and fault conditions  Normal completion  Time limit exceeded  Memory unavailable  Protection error; for ex: attempted write to read-only file  Arithmetic error; for ex: attempted division by zero Arithmetic  Time overrun; for ex: process waited longer than a specified maximum for an event  I/O failure I/O  Invalid instruction; for example: when a process tries to execute data (text)  Privileged instruction  Data misuse Data  Operating system intervention; for example: to resolve a deadlock Operating system  Fatal error   Block/Unblock ( suspension / resumption )   Synchronization  Synchronization is timekeeping which requires the coordination of events to operate a system in unisontimekeepingsystem   Communication  Deadlock Handling -  A deadlock is a situation in which two or more competing actions are each waiting for the other to finish, and thus neither ever does.  In an operating system, a deadlock is a situation which occurs when a process enters a waiting state because a resource requested by it is being held by another waiting process, which in turn is waiting for another resource. If a process is unable to change its state indefinitely because the resources requested by it are being used by other waiting process, then the system is said to be in a deadlock.operating systemstateresource   Debugging –  Debugging is a methodical process of finding and reducing the number of bugs, or defects, in a computer program or a piece of electronic hardware, thus making it behave as expected. Debugging tends to be harder when various subsystems are tightly coupled, as changes in one may cause bugs to emerge in another.bugscomputer programelectronic hardwaretightly coupled

Reasons for Creating Process/Program:  System initialization.  Execution of process creation system call by running a process.  A user request to create a new process.  Initiation of a batch job.

Reason for Terminating Process/Program :  User logs off  Process executes a service request to terminate  Error and fault conditions  Normal completion  Time limit exceeded  Memory unavailable  Protection error; for ex: attempted write to read-only file  Arithmetic error; for ex: attempted division by zero  Time overrun; for ex: process waited longer than a specified maximum for an event  I/O failure  Invalid instruction; for example: when a process tries to execute data (text)  Privileged instruction  Data misuse  Operating system intervention; for example: to resolve a deadlock  Fatal error

 Block/Unblock ( suspension / resumption )  Synchronization Synchronization is timekeeping which requires the coordination of events to operate a system in unison

 Communication  Deadlock Handling - A deadlock is a situation in which two or more competing actions are each waiting for the other to finish, and thus neither ever does. In an operating system, a deadlock is a situation which occurs when a process enters a waiting state because a resource requested by it is being held by another waiting process, which in turn is waiting for another resource. If a process is unable to change its state indefinitely because the resources requested by it are being used by other waiting process, then the system is said to be in a deadlock.

MAIN MEMORY MANAGEMENT  Allocation/de-allocation for processes, files, I/O.  Maintenance of several processes at a time  Keep track of who's using what memory  Movement of process memory to/from secondary storage.

FILE MANAGEMENT A file is a collection of related information defined by its creator. Commonly, files represent programs (both source and object forms) and data. The operating system is responsible for the following activities in connections with file management:   File creation and deletion.   Directory creation and deletion.   Support of primitives for manipulating files and directories.   Mapping files onto secondary storage.   File backup on stable (nonvolatile) storage media.

Debugging Debugging is a methodical process of finding and reducing the number of bugs or defects, in a computer program or a piece of electronic hardware, thus making it behave as expected. Debugging tends to be harder when various subsystems are tightly coupled, as changes in one may cause bugs to emerge in another.

I/O MANAGEMENT  Buffer caching system  Generic device driver code – these are the abstract interfaces and code for managing instances of and references to devices.  Drivers for each device - translate read/write requests into disk position commands.

SECONDARY STORAGE MANAGEMENT  Disks, Tapes, Optical  Free space management ( paging/swapping )  Storage allocation - what data goes and where or what disk it should be put on  Disk scheduling

NETWORKING  Communication system between distributed processors.  Getting information about files/processes/etc. on a remote machine.  Can use either a message passing or a shared memory model.

PROTECTION SYSTEMS Means controlling of access Depends on the attributes of the file and user Goals of Protection  Obviously to prevent malicious misuse of the system by users or programs.  To ensure that each shared resource is used only in accordance with system policies,  To ensure that errant programs cause the minimal amount of damage possible.  Note that protection systems only provide the mechanisms for enforcing policies and ensuring reliable systems.

SYSTEM PROGRAMS Command Interpreters -- Program that accepts control statements (shell, GUI interface, etc.) It is the part of an Operating System that interprets commands and carries them out. A command interpreter is the part of a computer operating system that understands and executes commands that are entered interactively by a human being or from a program. In some operating systems, the command interpreter is called the shell.

Compilers - is a computer program (or set of programs) that transforms source code written in a programming language(the source language ) into another computer language (the target language, often having a binary form known as object code ). Linkers - a computer program that takes one or more objects generated by a compiler and combines them into a single executable program. Communications (ftp, telnet, etc.)