Understanding the concept of paging in Operating System

In the absence of paging a process is loaded onto memory and executed. To increase degree of multi programming multiple processes are inserted into RAM and as and when process gets completed they are removed .

Key Take Aways.

• Process memory needs to be contiguous if paging is not implemented.
• Although 300 MB memory was available still Process 4 cannot be executed as 300 MB was fragmented and not contiguous.
• External fragmentation leads to performance degradation.
• This is the same issue what one faces with Hard disk fragmentation resulting in performance degradation.

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With the advent of paging  

• The concept of paging required the RAM to be divided in fixed size FRAMES and process memory footprint in Pages.
• The problem of External fragmentation is tackled by paging.
• A process is no more required to have contiguous memory footprint.
• Process is divided into pages and hence dynamic loading  also became possible .
• A page can be swapped in or out of RAM resulting in increasing degree of multiprogramming.
• A frame is the minimum level of transaction.

Cons of paging .

• If a process has a memory footprint of 150 still it will occupy  2 Frames (200 MB).  This results in a loss of 50 MB which is known as internal fragmentation.
• Frames are the minimum level of transaction that one can get.  Any request less than a frame is served by 1 Frame.

Linux commands to Find out the page size of the executed process

/usr/bin/time -v CMD
dstat (Live status about pages being brought in and swapped out)