Page fault rate is the number of page faults occurring during a number of memory references. If the page fault was designated as f, and the memory reference was listed as t, then the page fault rate can be expressed as P = f/t, where 0 ≤ P ≤ 1.
Page faults increase the time to access memory. The effective access time is the average time to access memory in the presence of page faults.
The time to access can be written as E = ((1-P)*m) + (P * S) where m is the time it takes to access physical memory (50-150 nanoseconds => 0.00000005 to 0.00000015 seconds), and S is the time to access the virtual memory (9-15 millseconds for a HDD => 0.009 -0.0015 seconds) or 35 to 100 microseconds for an SSD.
A HDD is considered to be approximately 1/200th the speed of DRAM (Dynamic Random Access Memory).
Thus we can see how much slower handling page faults makes our machine.
Load control is the activity of determining how many processes should be running concurrently at any given time to maximize overall system performance.
Thrashing is an execution state during which most of the time is spent on moving pages between the memory and the disk while the CPU is mostly idle and no process is making any real progress. This occurs when too many processes are sharing memory concurrently and no process has enough pages to operate without frequent page faults.
The page size has a major impact on the time and space overhead of virtual memory and thus on the overall performance of the system. The most common page sizes range between 512 and 4096, however, the best page size depends on many factors, some of which favor a large size while others favor a small size. Consequently, the page size is always a compromise.
Time & Space Efficiency of Virtual Memory was originally found on Access 2 Learn
