SWAPPING

Swapping is a technique of removing a process from main memory and storing it into secondary memory, usually a hard disk temporarily and then bringing it back into main memory for continued execution.

Swapping is a memory management technique used in multiprogramming environments which have limited memory capacity.

Thus, in Multiprogramming swapping may be used to increase the number of process sharing the CPU.

However, in Multiprogramming, there may arise a situation when all the active processes cannot be accomadated in the main memory.

In this case, one of the process may be moved out temporarily from main memory to secondary memory so as to create a sapce for another active process.

This action of moving a process out of main memory is called Swap out and the action of moving a process into the main memory is called swap in.

The area on the disk where the swapped out processes are stored is called Swap Space.

Backing store is a usually a hard disk drive or any other secondary storage which fast in access and large enough to accommodate copies of all memory images for all users. It must be capable of providing direct access to these memory images.


Swapping concept comes in terms of process scheduling.

Swapping is basically implemented by Medium term scheduler.

Medium term scheduler removes process from CPU for duration and reduce the degree of multiprogramming.

And after some time these process can again be reintroduced into main memory.

Swapping can be implemented in various ways. For example, swapping can be priority based. That means if a higher priority process arrives and wants service, the memory manager can swap out the lower priority process to the secondary memory so that it higher priority process can be loaded to main memory for execution.

As soon higher priority process finishes, the lower priority process will be swapped back to main memory and execution will be continued. Sometimes swapping is also called roll out, roll in                      
[12:34, 9/24/2017] myn: FILE MANAGEMENT

--------------------------------------------------------------------------------

File Management is the process of storing , managing the data stored on disks or secondary storage in the form of files.

A File Management system should not be confused with a file system, which manages all types of data and files includes a programming language for further data manipulation.

The system may contain features like: 

• Assigning queued document numbers for processing 
• Owner and process mapping to track various stages of processing 
• Report generation 
• Notes 
• Status 
• Create, modify, copy, delete and other file operations 

Conecpt Of File:

A File is a logical collection of information stored on Secondary Storage such as Hard Disk.

A File is the smallest allotment of secondary storage devices e.g. disk.

A File is a sequence of logical records that a sequence of bits and bytes.

Files can be used to contain data and programs.

Data files can be numeric, alphabetic, alphanumeric or binary.

A File has various attributes like name, type, location, size, protection, and date of creation etc.


File Naming:

A File can be given a name for the convenince of its use by its creator.

A name is attached to every file so as to uniquely identify it and access it through its name.

The exact rules for naming a file is vary from system to system. But all Operating System allow string of one to eight letters as legal file name.

Digits and some special characters are also allowed in file names.

Some systems differentiate between uppercase and lower case characters in names, whereas other systems consider the two cases equivalent.

For example: UNIX differentiate uppercase letters from the lowercase whereas MS-DOS does not.

Thus in UNIX, files Hello, hello, HeLlo, HELLO are different whereas in MS-DOS, they all represent same file