General purpose computers need to be able to access a variety of IO devices, from long term storage, mouse, keyboard, networking, and more. A device controller/adapter is an electronic circuit capable of operating a specific I/O device. The interface may be set by and/or examined by device drivers. A device driver is a device-specific program that implements I/O…
The file system sees a file as a series of blocks where the file physically exists on the disk. That disk block can only be accessed as a single unit using low-level read-block and write-block operations. In a contiguous block allocation scheme, every file is mapped into a contiguous sequence of disk blocks. The FCB points to the…
Creating or destroying a file effects the FCB with creation creating the FCB and allocating space for the file is only done when there is contents for the file, which often happens almost instantaneously, while deleting/destroying the file means that its resources are released so another use can use it. The Open File Table is…
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…
