Dos
DOS stands for Disk Operating System, an operating system used to control personal computers that is stored on a disk and loaded into memory each time the computer is booted up or powered on. DOS is the software that performs the essential tasks needed to make a computer operate, such as storing and retrieving files, opening application programs, and receiving input from the keyboard and mouse. It allows many different types of software applications, such as games and word processing, to operate on the same computer.
There are many different types of DOS, such as PC-DOS, DR-DOS, and N-DOS. The most common version is MS-DOS (Microsoft Disk Operating System). MS-DOS was developed by the Microsoft Corporation and became the foundation of the Windows operating system that is used in most personal computers today.
MS-DOS was developed in the early 1980s when IBM was designing its version of the personal computer; IBM and gave Microsoft the contract to develop the operating system. Microsoft bought the rights to an early version of DOS called QDOS (Quick and Dirty Operating System) and modified it to create MS-DOS. Bill Gates had the foresight to convince IBM to allow Microsoft to retain the right to license MS-DOS and it became the foundation of the company's fortune.
Microsoft developed a Graphical User Interface (GUI) called Windows that made it possible to execute DOS functions by using a mouse to select icons or pictures rather than by typing commands. Currently most users of personal computers work entirely in an environment created by a GUI operating system, such as the latest versions of Windows (which are no longer "shells" for DOS; that is, unlike Windows 3x, Windows 95, and Windows 98, these later incarnations--Windows NT, Windows 2000, Windows XP--are not "extensions" of DOS, they are operating systems that do not contain DOS code). However, there are computer users who prefer to work in a DOS environment or maintain older applications that must run from DOS, and innovative new versions of DOS are always under development.
When a DOS-based computer is first turned on, DOS is copied from the hard drive into memory and generates the "command line" interface that you use to tell the computer what to do. In some personal computers, DOS works together with a GUI program such as early versions of Windows to provide an icon-based interface that makes it easier for you to do tasks such as starting programs and opening files. If you work directly with the DOS interface, you must type text commands at the DOS command prompt.
For example, to delete a file with a GUI interface or operating system, you can use the mouse to click on the file folder icon where the file is stored, select the file from a list, and then press the delete key. In DOS you must type out a text command that includes the delete instruction, the location of the file, and the name of the file. For example, to delete a file called "report.doc" stored in a folder or directory called "C:\Work," you would have to type the following text after the "C:\>" command prompt:
del c:\work\report.doc
In order to control the storage and retrieval of data, DOS uses a specific structure to identify drives and file locations. Each drive is identified with a letter:
- Floppy drives are labeled A and possibly B.
- Hard drives start with the letter C and can continue to Z, though most personal computers use only one C drive. (That one physical drive, however, can be partitioned, or subdivided, to act like one or more hard drives, each with its own letter.)
- CD drives receive the letter after the last hard drive; typically D or E.
DOS organizes data or files in a hierarchy or tree structure consisting of root directories, directories, and sub-directories specified by the computer user. The root directory is usually the same as the disk drive letter, such as A or C. Files are stored in directories or subdirectories and accessed with a path name. For example, a resume stored on the C drive in a directory called "Work" and a subdirectory called "JobHunt" is accessed through the path: C:\work\jobhunt\resume.doc. The backslash (\) is used to show the divisions between directories and subdirectories. The backslash after the C: indicates that this is the root directory.
DOS file names include an extension at the end that tells DOS what function that file performs. For example, data files such as a letter created with a word processing program are typically given extensions such as .doc or .txt, as in resume.doc. Executable files, which are responsible for starting applications such as spreadsheet programs or games, are given the extension .com or .exe.
DOS commands allow you to control system settings such as the time and date, to manipulate files, and to read and input text with a basic text editor. Some common MS-DOS commands include:
- DEL, to Delete a file or files
- DIR, to Display the contents of a directory
- CD, to Change to a new directory
- COPY, to Copy a file from one directory to another
- EDIT, to open the text editor that comes with later versions of MS-DOS
Most DOS operating systems are also supported by two key system files that can be used to configure aspects of system performance. These files are executed each time DOS is started up:
- Config.sys: This file is used to configure the way DOS handles various system functions, typically those processes that occur in the "background." System settings such as certain memory allocation options, the amount of cache memory, virus-checking instructions, etc. are set here.
- Auotexec.bat: This file is a list of commands, each of which is used to configure the user environment. Programs can be started from this file, appearance options can be set, etc. This file is used to automate the process of customizing the DOS environment for a particular user.
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