virtual memory mgmt

principle of locality means

a process only accesses a small portion of its address space during any given period of time

virtual memory does not store the entire process image in main memory hence

signficantly increse the degree of multi-programming and even run a process with larger address space then the main memory

Principle of locality also referred to as

locality of reference

Principle of locality includes two types of locality

Spatial locality & Temporal locality

Spatial locality

Reference memory addressees near previously referenced addresse

Temporal locality

reference memory addresses that have been referenced in the past

Virtual Memory Challenge

Need to identify which portions of the address space of process should be stored in the main memory & The access pattern of a process may change over time

The rest of the process image is stored in a reserved section of the secondary storage known as

swap space

Portions of process image may need to move back and fourth between

main memory & swap space

Trade off between amount of information movement between main memory and swap space & amount of process image kept in memory are

lower degree of multi programming & too much information movement between main memory and swap space

What happens if too much of each process image is kept in main memory?

It lowers the degree of multiprogramming because fewer processes can fit in memory.

Why can a low degree of multiprogramming reduce CPU utilization?

If the few processes in memory are waiting for I/O, there may be no ready process for the CPU to execute.

Does low multiprogramming cause processes to perform more I/O?

No. It means fewer alternative processes are available while another process is waiting for I/O.

What is the trade-off in virtual memory management?

Keeping too much of each process in memory lowers multiprogramming, while keeping too little causes excessive paging between main memory and swap space.

What happens if too little of a process image is kept in main memory

It causes frequent page faults and excessive movement of pages between main memory and swap space. The process spends more time waiting for required parts of its address space to be loaded into memory.