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…
The optimal working set of a process is the set of pages that will be needed in the immediate future and thus should be resident in the physical memory. The size of the set will be based upon the size of the process and what it needs. To determine the size of the working window, the OS…
A reference string is the sequence of page numbers referenced by an executing program during a given time interval. Reference strings are used to compare different page replacement algorithms by counting the number of page faults generated. Since page faults are time consuming, the optimal page replacement algorithm selects the page that will not be referenced for the longest…
Virtual Memory (VM) is a collection of one or more logical address spaces, each of which may exceed the size of physical memory. To access this space, we use a virtual address. A paged virtual memory creates a single large contiguous address space per process. Demand paging is the principle of loading a page into memory only…
Now one issue that linked lists have is that while it’s really easy to move to the next element in your list, moving backwards to find the previous item is really challenging. You literally have to start back at the beginning and move through every element, until you reach the one before where you just…
There is a modification to the Linked List called a circular linked list. There is a current node which links to the next node, etc. This continues on until the “last” node, which points back to the first node. Circular lists work well where you need to always be pointing to the next element, and…
With paging, all components of a program, including code, static data, the stack, and other data structures, are combined into one contiguous address space divided into fixed-size pages. Segmentation addresses the problem by providing multiple logical address spaces for each process, where each segment can have a different size. A segment is a variable-size block of a…
The main disadvantage of dividing memory into variable partitions is external fragmentation, which requires the searching of memory for holes large enough to satisfy each request. As we’ve mentioned previously, swapping or compaction is necessary when no hole large enough is available. A page is a fixed-size contiguous block of a logical address space identified by the…
