Memory management

Paging

• a method of partitioning memory

• memory is split into equal sizes called ‘pages’

• pages are physical divisions

• programs are then split to fit into given number of pages

Segmentation

• a method of partitioning memory

• based on logical divisions of the program, segments are logical divisions with different sizes

• memory is partitioned according to this (check)

• takes into account how the program is written

physical divisions

check

logical divisions

When a program is broken up (segmented) logically, loops, functions or modules are all together and not separated.

What is virtual memory?

A section of the hard drive that acts as RAM when main memory is full. Sections of programs not currently in use are temporarily moved to virtual memory through paging.

What is disk thrashing?

When the computer freezes as a result of pages being swapped between the hard disk and main memory too frequently. More time is spent transferring pages opposed to running the program. Becomes worse as virtual memory is filled up.

Benefits of virtual memory

• facilitates effective multitasking

• allows more extensive programs to be run

Drawbacks of virtual memory

• disk thrashing

• Slower access speeds than physical memory

• Degrades performance if overused

Benefits of paging?

• Facilitates efficient memory management

• Enables the use of virtual memory

Drawbacks of paging?

• can lead to internal fragmentation

Benefits of segmentation?

• space-efficient due to only allocating space depending on the amount an application needs

Drawbacks of segmentation?

• can lead to external fragmentation

What is internal fragmentation?

• Wasted space within a page itself

• Other unrelated data cannot be stored in this space, more wasted space exists in main memory over time. This is internal fragmentation

What is external fragmentation?