In addition to the file name, file type, and other meta data, the file system has to keep track of various other pieces of data. How much data is stored is dependent upon the OS and it’s needs. Size – of the file Type – directory / executable file / data file / etc Location…
A file directory (or folder) is a special-purpose file that records information about other files and possibly other directories. The directory consists of a set of entries, each containing the name of a file followed by other information necessary to access the file. Directories and folders are technically different, especially under Windows. Windows provides other information about folders,…
Files present a way to store persistent data (that is data that doesn’t go away when a computer is either intentionally, or unintentionally, turned off). Older systems relied on tape, then magnetic disks, and now solid state media. A file system is used by the OS to manager and track the files on the media….
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…
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…
