Fundamentals of Computers

Computer Definition:

Computer is an electronic device, which process the data in to information. Data is simply collection of facts and figures. Data in computer is fed through input device and information comes on an output device. Processing which is actually the sequence of acts done on data to transform into information is done by the CPU (Central Processing Unit).

                          

                                                                               Block Diagram of a computer

It is very versatile electronic machine which is used these days almost all the places. Its versatility is mainly because of its speed, accuracy and powerful computing properties.

It consists of three essential components

1.       Input Devices

2.       CPU (Central Processing Unit)

3.       Output Devices

CPU consists of Memory Unit, ALU (Arithmetic and Logic Unit) and CU (Control Unit). ALU is responsible for the calculation and comparison applications on the data entered. CU controls the flow of the data between the Memory, ALU and the input / Output devices.

                Memory Unit consists of the Memory of the computer can be classified into Primary and Secondary Memory. Primary memory consists of semiconductor chips which can further be classified as

1.       Random Access Memory (RAM)

2.       Read Only Memory (ROM)

RAM (Volatile Memory) is the main memory where we work and edit our documents. It is temporary memory.

ROM (Non Volatile Memory) is the permanent memory where some permanent instructions are stored and are not erased when electricity goes off.

Secondary memory consists of storage devices like Floppy disks, Hard disks, Magnetic Tapes, CD-ROM, CD-R etc. The files and information is stored here is permanent in nature and can be erased only by the user. As we know that a computer is just a machine which works on our instructions or commands. The physical components of the computer are called Hardware and the set of instructions which make computer work is called Software. Attachments like Input / output devices attached with the CPU are called Peripheral devices.

             

Types of Computers:

Computers differ from each other on various aspects like in Type & Application and Computational power. We can divide computers in to three types

1)      Digital Computers: These computers operate by counting, using the information in the form of binary digits (0 and 1). These types of computers are very widely used in Business, Scientific purpose and also in Industry. Digital computer are most common type of computers which you can see people using everywhere.

2)      Analog Computers:  These computers measure the physical quantity instead of counting. Like temperature, voltage or pressure that fall or rise continuously. For example ordinary watch or speedometer is an analog device.

3)      Hybrid Computers: These computers combine the best features of both digital and analog computers. These are dual purpose computer has measuring capabilities of an analog computer and logical capabilities of a digital computer. These are generally used in intensive care units of hospitals, space vehicle simulation and also for many general purpose like converting the weight or quantity of petrol measured into the cost etc.

If you see computer from size, performance and computational power, you can divide them as Micro computers, Mini computers, Mainframe computers and Super computers.

 Micro computer: is the computer you use and see these days, using a microprocessor.

Minicomputer: comes somewhere between mainframe and micro computer. It is generally used as server in a multi user environ. It has more capacity and memory than micro computers.

Main frame computers: Mainframe computers are bulky computers with large storage capacities and lots of logic circuits inside and are used in large organizations.

Super computers: have tremendous speed containing thousands of fast processors are being developed. These processors work together in a single system to increase the processing power many folds. This type of processing is called parallel processing.

Memory:

Memory is classified in to two types

i)                    Main Memory

ii)                   Secondary Memory

Main memory is also called as Primary memory consists of semiconductor chips which can further be classified as

1.       Random Access Memory (RAM)

2.       Read Only Memory (ROM)

RAM (Volatile Memory) is the main memory where we work and edit our documents. It is temporary memory.

                                              

ROM (Non Volatile Memory) is the permanent memory where some permanent instructions are stored and are not erased when electricity goes off.

                                               

Secondary memory consists of storage devices like Floppy disks, Hard disks, Magnetic Tapes, CD-ROM, CD-R etc. The files and information is stored here is permanent in nature and can be erased only by the user. As we know that a computer is just a machine which works on our instructions or commands.

Cache memory: is random access memory (RAM) that a computer microprocessor can access more quickly than it can access regular RAM. As the microprocessor processes data, it looks first in the cache memory and if it finds the data there (from a previous reading of data), it does not have to do the more time-consuming reading of data from larger memory. 

                                        

Input Device:

 A part which provides man to machine (computer) communication. Data or instructions can be give to the computer through it. Input of any form is first convert into binary electronic signals which can understand by the computer (CPU). Some of the Input devises are Keyboard, Mouse, Track Ball, Magnetic Ink Character Reader (MICR), Bar Code Reader (BCR), Optical Character Reader, scanner and Microphone etc.

     

Output Device:

Used for machine to man communication. After processing the data displays the information though it. It converts the Binary electronic signals of output to the human understandable form. Some of  the output devises are Monitor, Printer, Speaker, Plotter etc.

     

An operating system (OS) is an interface between a computer user and its hardware.  It is software, consisting of programs and data, that runs on computers and manages the computer hardware and provides common services for efficient execution of various application software.

Functions:

Communication: Facilitates easy communication between the user and computer system.

Processor  management: It assigns the processor to different tasks performed by the computer.

Memory management: It allocates the main memory to data, application programs and system programs.

Input / Output management: It sends the required input / Output to the input / output devices as mentioned in the program.

File management: It is one of the major functions of the operating system. All files created are stored, retrieved and modified by the operating system. So the programmer is free to think on development aspect only.

                                                               

An operating system is a software component of a computer system that is responsible for the management of various activities of the computer and the sharing of computer resources. It hosts the several applications that run on a computer and handles the operations of computer hardware. Users and application programs access the services offered by the operating systems, by means of system calls and application programming interfaces. Users interact with operating systems through Command Line Interfaces (CLIs) or Graphical User Interfaces known as GUIs. In short, operating system enables user interaction with computer systems by acting as an interface between users or application programs and the computer hardware. Here is an overview of the different types of operating systems.

Real-time Operating System: It is a multitasking operating system that aims at executing real-time applications. Real-time operating systems often use specialized scheduling algorithms so that they can achieve a deterministic nature of behavior. The main object of real-time operating systems is their quick and predictable response to events. They either have an event-driven or a time-sharing design. An event-driven system switches between tasks based of their priorities while time-sharing operating systems switch tasks based on clock interrupts.

Multi-user and Single-user Operating Systems: The operating systems of this type allow a multiple users to access a computer system concurrently. Time-sharing system can be classified as multi-user systems as they enable a multiple user access to a computer through the sharing of time. Single-user operating systems, as opposed to a multi-user operating system, are usable by a single user at a time. Being able to have multiple accounts on a Windows operating system does not make it a multi-user system. Rather, only the network administrator is the real user. But for a Unix-like operating system, it is possible for two users to login at a time and this capability of the OS makes it a multi-user operating system.

Multi-tasking and Single-tasking Operating Systems: When a single program is allowed to run at a time, the system is grouped under a single-tasking system, while in case the operating system allows the execution of multiple tasks at one time, it is classified as a multi-tasking operating system. Multi-tasking can be of two types namely, pre-emptive or co-operative. In pre-emptive multitasking, the operating system slices the CPU time and dedicates one slot to each of the programs. Unix-like operating systems such as Solaris and Linux support pre-emptive multitasking. Cooperative multitasking is achieved by relying on each process to give time to the other processes in a defined manner. MS Windows prior to Windows 95 used to support cooperative multitasking.

Distributed Operating System: An operating system that manages a group of independent computers and makes them appear to be a single computer is known as a distributed operating system. The development of networked computers that could be linked and communicate with each other, gave rise to distributed computing. Distributed computations are carried out on more than one machine. When computers in a group work in cooperation, they make a distributed system.

Embedded System: The operating systems designed for being used in embedded computer systems are known as embedded operating systems. They are designed to operate on small machines like PDAs with less autonomy. They are able to operate with a limited number of resources. They are very compact and extremely efficient by design. Windows CE, FreeBSD and Minix 3 are some examples of embedded operating systems.

Batch processing: As clear from the name, processing work is taken up in batches by the CPU. Here several programs are collected and read onto the storage device like disk or tape to form a queue of programs. As CPU finishes processing of the one program, it is ready to take up another program from the input medium(Disk or tape). Like in banks, all the transactions which are done in the morning are entered collectively in evening in the main computer. After that all the accounts are updated and cash available in the bank is tallied. Today this type of time delays in not acceptable, so we have interactive systems.

Multi Programming:

In the batch processing, there can be a single program present in the main memory for the processing and that may not avail the full capabilities of the CPU. Program might not be large enough to fit in the whole memory making rest of the memory unutilized or program may be such that most of the time it is reading data and writing it as information and includes very few calculations leaving for the CPU idle most of the time.  For example, a program which reads list of names from the disk and print those on the paper don’t involve calculations, so majority of the work it is performing is input-output.

The solution this is using multi-programming system which makes more than one program to reside in the memory possible. Suppose there are three programs let us say A, B and C are residing in the memory. When one program is busy in reading or writing of data, calculations and processing involved in other program can be done. When one program finishes its processing, next program takes it place.

multitasking :In computing, multitasking is a method by which multiple tasks, also known as processes, share common processing resources such as a CPU. In the case of a computer with a single CPU, only one task is said to be running at any point in time, meaning that the CPU is actively executing instructions for that task. Multitasking solves the problem by scheduling which task may be the one running at any given time, and when another waiting task gets a turn. The act of reassigning a CPU from one task to another one is called a context switch. When context switches occur frequently enough the illusion of parallelism is achieved. Even on computers with more than one CPU (called multiprocessor machines), multitasking allows many more tasks to be run than there are CPUs.

 time-sharing : systems, the running task is required to relinquish the CPU, either voluntarily or by an external event such as a hardware interrupt. Time sharing systems are designed to allow several programs to execute apparently simultaneously. The expression 'time sharing' was usually used to designate computers shared by interactive users at terminals, such as IBM's TSO, and VM/CMS

real-time : systems, some waiting tasks are guaranteed to be given the CPU when an external event occurs. Real time systems are designed to control mechanical devices such as industrial robots, which require timely processing.

The development of MS-DOS

MS-DOS is the most well known operating system, the most commercialised version is that of Microsoft, christened "MS-DOS" (there are other versions such as DR-DOS). MS-DOS was created in 1981 when it was used on an IBM PC.

Introduction to the operating system

DOS, as with any operating system, controls computer activity. It manages operations such as data flow, display, data entry amongst other various elements that make up a system.
The role of DOS is to interpret commands that the user enters via the keyboard.
These commands allow the following tasks to be executed:

• file and folder management
• disk upgrades
• hardware configuration
• memory optimisation
• program execution

These commands are typed after the prompt, in the case of MS-DOS (Microsoft DOS, the most well known): the drive letter followed by a backslash, for example: A:\ or C:\.

Internal Commands: (in COMMAND.COM)

BREAK, CALL, CD, CHCP, CHDIR, CLS, COPY, CTTY, DATE, DEL, DIR, ECHO, ERASE, EXIT, FOR, GOTO, IF, MD, MKDIRr, PATH, PAUSE, PROMPT, RD, REM, REN, RENAME, RMDIR, SET, SHIFT, TIME, TYPE, VER, VERIFY, VOL

  External Commands: (.COM and .EXE programs)

APPEND, ASSIGN, ATTRIB, BACKUP, CHKDSK, COMMAND, COMP, DEBUG, DEFRAG, DISKCOMP, DISKCOPY, DOSSHELL, EDIT, EDLIN, EXE2BIN, FASTOPEN, FC, FDISK, FIND, FORMAT, GRAFTABL, GRAPHICS, HELP, JOIN, KEYB, LABEL, LINK, MEM, MODE, MORE, MSD, NLSFUNC, PRINT, QBASIC, RECOVER, REPLACE, RESTORE, SELECT, SHARE, SORT, SUBST, SYS, TREE, XCOPY
>External Commands / DOS version

A desktop computer is a personal computer (PC) in a form intended for regular use at a single location, as opposed to a mobile laptop or portable computer. Prior to the widespread use of microprocessors, a computer that could fit on a desk was considered remarkably small. Desktop computers come in a variety of types ranging from large vertical tower cases to small form factor models that can be tucked behind an LCD monitor. "Desktop" can also indicate a horizontally-oriented computer case usually intended to have the display screen placed on top to save space on the desktop. Most modern desktop computers have separate screens and keyboards. Tower cases are desktop cases in the earlier sense, though not in the latter. Cases intended for home theater PC systems are usually considered to be desktop cases in both senses, regardless of orientation and placement

                                                      

Folder, directory,^[1] catalog, or drawer,^[2] in computing, is a virtual container within a digital file system, in which groups of computer files and other folders can be kept and organized.
A typical file system may contain thousands (or even hundreds of thousands) of folders. Files are kept organized by storing related files in the same folder. The folder can also be referred to as the root. A folder contained inside another folder is called a subfolder or subdirectory or child of that folder. Together, the folders form a hierarchy, or tree structure.

My Computer

A section of Microsoft Windows that was introduced with the release of Microsoft Windows 95 and included with all versions of Windows after that. My Computer allows the user to explore the contents of their computer drives as well as manage their computer files. To the right, the top image is an example of the My Computer icon in Microsoft Windows XP. With the introduction of Windows Vista, Microsoft changed the traditional My Computer icon to Computer, the bottom image to the right is an example of what this icon looks like. Although the name has changed this icon still acts identical to the earlier My Computer.
How to open My computer

1. Get to the Windows Desktop.
2. Double-click the My Computer icon, this icon is almost always located on the top-left portion of the desktop and should look similar to the icon above. Below are two examples of what should appear when My Computer is open. If this icon is missing see document CH000927.

Drive listing in My Computer

Browsing My Computer in Windows 2000

Using My Computer

Once My Computer is open you'll see all available drives on your computer. For most users you'll only be concerned with the Local Disc (C:) drive. This is your hard disk drive and what all your files are stored on. Double-click this drive icon to open it and view of its contents.

If you're looking for a document such as a word processor file you've created, music file, picture, or other personal file it's likely that it's contained in your documents folder. This folder is displayed in My computer as a folder and usually contains your name. For example, if your username was John, this folder would be named John's Documents.

Finding files in My Computer

If you're having trouble finding where one of your files is stored use the Windows find feature to quickly find the file. To do this from within My Computer either click on File and then Search or right-click on the C: drive or other folder you wish to search and click Search.

In the Search window type the name or part of the name of the file you're looking for.

Adjust system settings with your computer

If you wish to manage your computer or view other settings and information about your computer instead of double-clicking the My Computer icon to open it, right-click on the My Computer icon and click Properties. Performing these steps will open your System Properties (the same window accessible through the Control Panel).

My Documents

On Microsoft Windows computer operating systems (except for Windows NT), My Documents is the name of a special folder on the computer's hard drive that the system commonly uses to store a user's documents, music, pictures, downloads, and other files.

Overview

Microsoft first introduced the "My Documents" folder in Windows 95 OEM Service Release 2, as a standard location for storing user-created files. The folder - located under the root of the hard drive that Windows is installed on - is displayed (but not stored) directly on the user's desktop.

"My Documents" as it appears in Windows XP

In Windows 2000, Windows XP and Windows Server 2003 set up the "My Documents" folder (by default) in the user's profile directory, as Documents and Settings\[user name]\My Documents on the same hard drive that Windows is installed on. Note that "My Documents" in these operating systems is one of a number of Special Folders - a concept introduced in Windows 2000 to add a layer of abstraction between the user interface's presentation of the folder and its physical location and contents. As such, "My Documents" in file load/save dialogs (and in Windows Explorer) doesn't appear as an absolute path. A user can change the physical location of "My Documents" by right-clicking on the "My Documents" icon, selecting the Properties option, and entering a new folder location (path) in the Target tab.
Windows Vista renames "My Documents" as, simply, "Documents". "My Music", "My Pictures" and "My Videos" have also lost their prefix, and have moved to directly under the user's profile directory (C:\Users\[user name]).
As of Windows 7, The "Documents", "Pictures", "Music" and "Videos" folders appear displayed in Windows Explorer with a "My" prefix but are actually still stored in the file system without the prefix (as in Windows Vista).
An application can convert environment strings in a user-supplied path (e.g. "%HOMEPATH%\My Documents") to an actual path by (for example) calling the function ExpandEnvironmentStrings.

Recycle Bin (Windows)

In the Microsoft Windows operating systems, the Recycle Bin is a holding area for files and folders that are held before final deletion from a storage device.

Recycle Bin in Windows Vista.

General

Microsoft introduced the Recycle Bin in the Windows 95 operating system. The Recycle Bin keeps some files that have been deleted, whether accidentally or intentionally. Whether a deleted file is put into the Recycle Bin depends on how it is deleted; typically only files deleted via the Explorer graphical interface (but not necessarily other Windows graphical interfaces such as file selection dialogs) will be put into the Recycle Bin; files deleted via the Command Prompt, or via operating system APIs are not. Users can review the contents of the Recycle Bin before deleting the items permanently. In previous Windows operating systems and in MS-DOS, undeletion was the only way to recover accidentally deleted files. The Recycle Bin holds data that not only lists deleted files, but also the date, time and the path of those files. The Recycle Bin is opened like an ordinary Windows Explorer folder and the files are viewed similarly. Deleted files may be removed from the Recycle Bin by restoring them with a command, or by deleting them permanently.
The Recycle Bin only stores files deleted from hard drives, not from removable media, such as memory cards and floppy disks. It also doesn't store files deleted from network drives.
The Recycle Bin's icon indicates whether there are items in the Recycle Bin. If there are no files or folders in the Recycle Bin, then the icon resembles an empty wastepaper basket. Otherwise if there are files and/or folders the icon resembles a full wastepaper basket.
Prior to Windows Vista, the default configuration of the Recycle Bin was to hold 10% of the total capacity of the host hard disk drive. For example, on a hard drive with a capacity of 20 gigabytes, the Recycle Bin will hold up to 2 gigabytes. If the Recycle Bin fills up to maximum capacity, the oldest files will be deleted in order to accommodate the newly deleted files. If a file is too large for the Recycle Bin, the user will be prompted to permanently delete the file instead.
Windows Internet Explorer (formerly Microsoft Internet Explorer; commonly abbreviated to IE), is a series of graphical web browsers developed by Microsoft and included as part of the Microsoft Windows line of operating systems starting in 1995. It was first released as part of the add-on package Plus! for Windows 95 that year. Later versions were available as free downloads, or in service packs, and included in the OEM service releases of Windows 95 and later versions of Windows.

Windows Explorer is a file manager application that is included with releases of the Microsoft Windows operating system from Windows 95 onwards. It provides a graphical user interface for accessing the file systems. It is also the component of the operating system that presents many user interface items on the monitor such as the taskbar and desktop. Controlling the computer is possible without Windows Explorer running (for example, the File | Run command in Task Manager on NT-derived versions of Windows will function without it, as will commands typed in a command prompt window). It is sometimes referred to as the Windows Shell, explorer.exe, or simply “Explorer”.

Languages:

)A programming language such as C, FORTRAN, or Pascal that enables a programmer to write programs that are more or less independent of a particular type of computer. Such languages are considered high-level because they are closer to human languages and further from machine languages. In contrast, assembly languages are considered low-level because they are very close to machine languages.
The main advantage of high-level languages over low-level languages is that they are easier to read, write, and maintain. Ultimately, programs written in a high-level language must be translated into machine language by a compiler or interpreter.
The first high-level programming languages were designed in the 1950s. Now there are dozens of different languages, including Ada, Algol, BASIC, COBOL, C, C++, FORTRAN, LISP, Pascal, and Prolog.
In computer science, a low-level programming language is a programming language that provides little or no abstraction from a computer's instruction set architecture. The word "low" refers to the small or nonexistent amount of abstraction between the language and machine language; because of this, low-level languages are sometimes described as being "close to the hardware."
A low-level language does not need a compiler or interpreter to run; the processor for which the language was written is able to run the code without these. This results in faster processing and a smaller file size when compared to the equivalent program in a high-level language.
By comparison, a high-level programming language isolates the execution semantics of a computer architecture from the specification of the program, making the process of developing a program simpler and more understandable.
Low-level programming languages are sometimes divided into two categories: first generation, and second generation.

First Generation (1940-1956) Vacuum Tubes The first computers used vacuum tubes for circuitry and magnetic drums for memory, and were often enormous, taking up entire rooms. They were very expensive to operate and in addition to using a great deal of electricity, generated a lot of heat, which was often the cause of malfunctions. First generation computers relied on machine language, the lowest-level programming language understood by computers, to perform operations, and they could only solve one problem at a time. Input was based on punched cards and paper tape, and output was displayed on printouts. The UNIVAC and ENIAC computers are examples of first-generation computing devices. The UNIVAC was the first commercial computer delivered to a business client, the U.S. Census Bureau in 1951.

Second Generation (1956-1963) Transistors

Transistors replaced vacuum tubes and ushered in the second generation of computers. The transistor was invented in 1947 but did not see widespread use in computers until the late 1950s. The transistor was far superior to the vacuum tube, allowing computers to become smaller, faster, cheaper, more energy-efficient and more reliable than their first-generation predecessors. Though the transistor still generated a great deal of heat that subjected the computer to damage, it was a vast improvement over the vacuum tube. Second-generation computers still relied on punched cards for input and printouts for output.
Second-generation computers moved from cryptic binary machine language to symbolic, or assembly, languages, which allowed programmers to specify instructions in words. High-level programming languages were also being developed at this time, such as early versions of COBOL and FORTRAN. These were also the first computers that stored their instructions in their memory, which moved from a magnetic drum to magnetic core technology.
The first computers of this generation were developed for the atomic energy industry.

Third Generation (1964-1971) Integrated Circuits

The development of the integrated circuit was the hallmark of the third generation of computers. Transistors were miniaturized and placed on silicon chips, called semiconductors, which drastically increased the speed and efficiency of computers.
Instead of punched cards and printouts, users interacted with third generation computers through keyboards and monitors and interfaced with an operating system, which allowed the device to run many different applications at one time with a central program that monitored the memory. Computers for the first time became accessible to a mass audience because they were smaller and cheaper than their predecessors.

Fourth Generation (1971-Present) Microprocessors

The microprocessor brought the fourth generation of computers, as thousands of integrated circuits were built onto a single silicon chip. What in the first generation filled an entire room could now fit in the palm of the hand. The Intel 4004 chip, developed in 1971, located all the components of the computer—from the central processing unit and memory to input/output controls—on a single chip.
In 1981 IBM introduced its first computer for the home user, and in 1984 Apple introduced the Macintosh. Microprocessors also moved out of the realm of desktop computers and into many areas of life as more and more everyday products began to use microprocessors.
As these small computers became more powerful, they could be linked together to form networks, which eventually led to the development of the Internet. Fourth generation computers also saw the development of GUIs, the mouse and handheld devices.

Fifth Generation (Present and Beyond) Artificial Intelligence

Fifth generation computing devices, based on artificial intelligence, are still in development, though there are some applications, such as voice recognition, that are being used today. The use of parallel processing and superconductors is helping to make artificial intelligence a reality. Quantum computation and molecular and nanotechnology will radically change the face of computers in years to come. The goal of fifth-generation computing is to develop devices that respond to natural language input and are capable of learning and self-organization.
BOOTing:
When the computer is switched on, the firmware program in Read Only Memory(ROM) also called Basic Input-Output System(BIOS) reads programs and data i.e. Operating System and loads it into memory (RAM). This process is known Bootstrapping(Booting). The OS once loaded takes control of the computer, handles user interaction and executes application programs.
During Booting process, computer loads the operating system into its memory. DOS booting involves reading following files into memory namely IO.SYS, MSDOS.SYS, and COMMAND COM. The Basic Input/Output Program (IO.SYS): This program provides interface between the hardware devices and software of the system. It takes care of the keyboard input, character output to monitor, output to printer and time of the day. The File and Disk Manager Program (MSDOS.SYS) : It contains the file management and the disk buffering management capabilities. It keeps track of all the disk access of an application program and remains permanently in memory. The Command Processor (COMMAND.COM) : It is also called command interpreter. It is the program that displays the system prompt and handles user interface by executing the command typed in by the user using keyboard.
 The CONFIG.SYS file : This file contains reference to device drivers which are loaded when OS takes control of the computer. This device drivers are required for configuring operating system for running special devices.
 The AUTOEXEC.BAT file : This is a special batch program that is automatically executed when the system is started. It can be used to define keys, define the path that MS-DOS uses to find files, display messages on the screen etc. It will be executed only if it exists in the root directory or the diskette from which the system is loaded. Each time the system is started, MS-DOS executes the commands stored in AUTOEXEC.BAT file. One can run it without restarting the system by typing AUTOEXEC at the command prompt.
Disk/Drives :
The user can store data or programs on secondary storage devices called Hard disk or Floppy disk. Physically disks store data by recording any pattern of magnetic changes on using a tiny read-write head that moves over the surface. Disk is divided into sectors and tracks. The first two characters of alphabet (a: or b:) are reserved for Floppy disks, Hard disks are identified by characters (c:) or (d:), the next character in the sequence is assigned to Compact Disk (CD-ROM) drive further the network drives connected to the system are assigned the remaining characters.
Directory :
It is a special type of file that contains other files. The relation between files, directories and disk is very similar to the relation between papers, filing folders and filing cabinets. The hierarchy in which directories are kept is called a tree structure.
Definition of a file : File Names
Information or data is stored is stored on a disk in the form of a file. When storing any file, it must be given a unique name, which can be used for subsequent identification/reference. Filenames should not be longer than 8 characters, can have an extension which should not be longer than 3 characters. Following characters are valid in a filename : A to Z , a to z, 0 to 9, !,@#$%&(){}_-\’. Different files are identified by their extensions. File which have extension EXE, COM, BAT are executable files. They can be executed by just typing their name at the command prompt. Extensions TXT, DOC, BAK, BAS, C represent text file, Documentation (MS-Word) file, Backup file, basic program file, C program file respectively.


Wildcards Definition
To retrieve and identify file, we can use its specific name or may refer to it with the help of wildcards which can even refer to entire group of files. There are two wild card symbols : asterisk (*) indicates that any or a one valid character can occupy that position or of the remaining positions in the filename or extension, Question mark (?) means that any one valid character can occupy that position.
Warm and COLD Reboot
Switching on of the computer from Power off and loading the operating system is called "Cold Boot". This generally starts with memory test and chips initialization.
There may be case when the computer is already on or has hanged up and we want to reboot the system. This is known as "Warm Boot" and is done by pressing ctrl+alt+del keys simultaneously or just by pressing "Reset" button on the system.
DOS Internal and External Commands: Command.com has built in commands, the so called "internal" commands and a few of them are "dir", "type", "vol", "date", etc. These commands are 'programmed' into the command.com file and do not require other files in order to work. On the other hand, we have commands such as "deltree", "undelete", "xcopy", etc. that are external commands, meaning that they require the actual application/file in order to use them, along with command.com.

DOS Internal Commands

The DOS (Windows 9x) internal commands are so-called because their instructions are a part of COMMAND.COM, the DOS (Windows 9x) command line interpreter.

Recall that COMMAND.COM is placed into memory each time the DOS or Windows 9x OS is booted. Thefore, the internal commands are always in memory and can always be executed from any command line prompt.

This is in contrast to the disk-bound external commands, which reside in secondary memory up until the moment they are needed, at which time the OS must find them and load them into primary memory.

The syntax for some frequently used internal commands follows.

   TIME

   Displays current time and allows it to be changed.

   Syntax: TIME

   DATE

   Displays current date and allows it to be changed.

   Syntax: DATE

   CLS

   Clears the screen.

   Syntax: CLS

   DIR

   Shows directory information of a diskette: name, size, and the

   date and time stamp of files.

   Syntax: DIR  [d:][path]

    Optional switches:

    /p  Display dir info and pauses display when the screen is full

    /w  Display names and extensions only in five columns

    To display a file directory listing for D:\LET\ANNUAL

        D:\LET\ANNUAL>DIR                  (from D:\LET\ANNUAL)

        D:\DATA>DIR  \LET\ANNUAL           (from D:\DATA)

        C:\WINDOWS>DIR  D:\LET\ANNUAL      (from C:\WINDOWS)

   <="" a="">

   COPY

   Copies a file. Name of copy may be the same as original, or different.

   Syntax: COPY [d:][path][name.ext]  [d:][path][name.ext]

    Optional switches:

    /v  Verify, copies the file and compares it with the original

    /b  Binary file

    To copy a file from D:\BATCH to the root of A: drive

        A:\>COPY  D:\BATCH\CL.BAT                (from A: drive)

        D:\BATCH>COPY  CL.BAT  A:\               (from D:\BATCH)

    To copy a file from the root of C: to A: drive and change its name

        A:\>COPY  C:\MSDOS.SYS  MSDOSSYS.BAK     (from A:)

        C:\>COPY  MSDOS.SYS  A:\MSDOSSYS.BAK     (from the root of C:)

    To copy all of the files from the root of A: to D:\CCV\ENGCOMP

        A:\>COPY  *.*  D:\CCV\ENGCOMP            (from A:)

        D:\CCV\ENGCOMP>COPY  *.*  A:\            (from D:\CCV\ENGCOMP)

   TYPE

   Displays the contents of a file.

   Syntax: TYPE [d:][path][name.ext]

   To display the contents of the file MY.LET to the screen

        A:\>TYPE  MY.LET

   DEL

   Deletes a file from disk.

   Syntax: DEL [d:][path][name.ext]

    To delete one file:

        A:\>DEL  A:\MY.LET 

    To del all files in current directory

        A:\>DEL  *.*

   REN

   Renames a file.

   Syntax: REN [d:][path][name.ext] [d:][path][newname.ext] 

    To change the name of the file D:\LET\ANNUAL\99.DOC to 1999.DOC

        D:\LET>REN  ANNUAL\99.DOC  1999.DOC             (from D:\LET)

        D:\DATA>REN  \LET\ANNUAL\99.DOC  1999.DOC       (from D:\DATA)

        C:\WINDOWS>REN  D:\LET\ANNUAL\99.DOC  1999.DOC  (from C:\WINDOWS)

   MD

   Makes (creates) a new directory.

   Syntax: MD [d:][path][dirname]

    To create a directory named HERMIT in the root of D: drive

        D:\>MD HERMIT                       (from D:\)

        C:\>MD D:\HERMIT                    (from C:\)

   RD

   Removes an existing directory            (directory must be empty). 

   Syntax: RD [d:][path][dirname]

    To remove the HERMIT sub-directory

        D:\>RD HERMIT                       (from D:\)

        C:\>RD D:\HERMIT                    (from C:\)

   CD

   Changes the current directory.

   Syntax: CD [path][dirname]

    To make D:\HERMIT the current directory

        D:\>CD  HERMIT                      (from D:\)

        D:\DATA>CD  \HERMIT                 (from D:\DATA)

        D:\DATA\SOURCE>CD \HERMIT           (from D:\DATA\SOURCE)

        D:\DATA\SOURCE>CD ..                (from D:\DATA\SOURCE)

   PATH

   The PATH command is used to help the command interpreter find 

   external commands which are not in the current directory. The 

   command interpretter looks into the 

DOS External Commmands Handout

Instructions for external commands are disk-based. This means the file with the name of the command must be loaded into RAM at the moment when the command is given. Application programs are external commands and some DOS programs are external. The syntax for some of the more useful DOS external commands, including their parameters and switches follow:
FORMAT
Prepares a diskette for use by DOS.

Syntax: FORMAT [d:]

Parameters: [d:] = Drive which is to receive the format.

Optional switches:

• /s Include all system files necessary to make disk "bootable"
• /b Reserve space for system files on diskette. (Formats 320k instead of 360k).
• /v Volume label of 11 characters

Some examples:

• To format a diskette in drive B: without system files:

FORMAT B:

• To format a diskette in drive A: with system files:

FORMAT A: /s

• To give the formatted diskette a volume name, include the /v switch:

FORMAT A: /V

• Combine switches to format a boot diskette with a volume label:

FORMAT A: /S /V

CHKDSK
Analyzes disk or diskette (first and only parameter) and displays disk and memory status report.

Syntax: CHKDSK [d:] [/f] [/v]

Parameters: [d:] = Drive upon which to perform the checkdisk.

Optional switches:

• /f Fix. Writes lost clusters to a disk file and corrects file allocation table.
• /v Verbose. Lists all files on a disk.

Example:

• To display statistics about the diskette in drive A:

CHKSDK A:

• To display statistics about the first hard disk and fix any lost clusters:

CHKSDK A: /f

DISKCOPY
Makes an exact copy of a diskette, including hidden system files if they are present.

Syntax: DISKCOPY [d1:] [d2:]

Parameters:[d1:] = Drive for source diskette, [d2:] = Drive for target diskette.
Example:

• To make an exact copy of a diskette in drive A: to a diskette in B:

DISKCOPY A: B:

• To make an exact copy of a diskette using only drive A:

DISKCOPY A: A:

(Change source and target diskettes as requested).

DISKCOPY asks for a SOURCE diskette (the diskette being copied) and a TARGET diskette (the diskette being copied to). The TARGET diskette need not be formatted, DOS will format it while doing the DISKCOPY. If the SOURCE diskette is bootable, the system will be transferred to the TARGET as well. The two disk drives must always use the same media.

List of DOS Commands:

APPEND

(External)
APPEND ;
APPEND [d:]path[;][d:]path[...]
APPEND [/X:on|off][/path:on|off] [/E]
Displays or sets the search path for data files. DOS will search the specified path(s) if the file is not found in the current path.

ASSIGN

(External)
ASSIGN x=y [...] /sta
Redirects disk drive requests to a different drive.

ATTRIB

(External)
ATTRIB [d:][path]filename [/S]
ATTRIB [+R|-R] [+A|-A] [+S|-S] [+H|-H] [d:][path]filename [/S]
Sets or displays the read-only, archive, system, and hidden attributes of a file or directory.

BACKUP

(External)
BACKUP d:[path][filename] d:[/S][/M][/A][/F:(size)] [/P][/D:date] [/T:time] [/L:[path]filename]

Makes a backup copy of one or more files. (In DOS Version 6, this program is stored on the DOS supplemental disk.)

BREAK

(Internal)
BREAK =on|off
Used from the DOS prompt or in a batch file or in the CONFIG.SYS file to set (or display) whether or not DOS should check for a Ctrl + Break key combination.

BUFFERS

(Internal)
BUFFERS=(number),(read-ahead number)
Used in the CONFIG.SYS file to set the number of disk buffers (number) that will be available for use during data input. Also used to set a value for the number of sectors to be read in advance (read-ahead) during data input operations.

CALL

(Internal)
CALL [d:][path]batchfilename [options]
Calls another batch file and then returns to current batch file to continue.

CHCP

(Internal)
CHCP (codepage)
Displays the current code page or changes the code page that DOS will use.

CHDIR

(Internal)
CHDIR (CD) [d:]path
CHDIR (CD)[..]
Displays working (current) directory and/or changes to a different directory.

CHKDSK

(External)
CHKDSK [d:][path][filename] [/F][/V]
Checks a disk and provides a file and memory status report.

CHOICE

(Internal)
CHOICE [/C[:]keys] [/N][/S][/T[:]c,nn] [text]
Used to provide a prompt so that a user can make a choice while a batch program is running.

CLS (Clear Screen)

(Internal)
CLS
Clears (erases) the screen.

COMMAND

(External)
COMMAND [d:][path] [device] [/P][/E:(size)] [/MSG][/Y [/C (command)|/K (command)]
Starts a new version of the DOS command processor (the program that loads the DOS Internal programs).

COMP

(External)
COMP [d:][path][filename] [d:][path][filename] [/A][/C][/D][/L][/N:(number)]
Compares two groups of files to find information that does not match. (See FC command).

COPY

(Internal)
COPY [/Y|-Y] [/A][/B] [d:][path]filename [/A][/B] [d:][path][filename] [/V]
or
COPY [/Y|-Y][/A][/B] [d:][path]filename+[d:][path]filename[...][d:][path][filename] [/V]
Copies and appends files.

COUNTRY

(Internal)
COUNTRY=country code,[code page][,][d:][filename]
Used in the CONFIG.SYS file to tell DOS to use country-specific text conventions during processing.

CTTY

(Internal)
CTTY (device)
Changes the standard I/O (Input/Output) device to an auxiliary device.

DATE

(Internal)
DATE mm-dd-yy
Displays and/or sets the system date.

DBLSPACE

(External)
DBLSPACE / automount=drives
DBLSPACE /chkdsk [/F] [d:]
DBLSPACE /compress d: [/newdrive=host:] [/reserve=size] [/F]
DBLSPACE /create d: [/newdrive=host:] [/reserve=size] [/size=size]
DBLSPACE /defragment [d:] ]/F]
DBLSPACE /delete d:
DBLSPACE /doubleguard=0|1
DBLSPACE /format d:
DBLSPACE [/info] [d:]
DBLSPACE /list
DBLSPACE /mount[=nnn] host: [/newdrive=d:]
DBLSPACE /ratio[=ratio] [d:] [/all]
DBLSPACE /size[=size] [/reserve=size] d:
DBLSPACE /uncompress d:
DBLSPACE /unmount [d:]
A program available with DOS 6.0 that allows you to compress information on a disk.

DEBUG

(External)
DEBUG [pathname] [parameters]
An MS-DOS utility used to test and edit programs.

DEFRAG

(External)
DEFRAG [d:] [/F][/S[:]order] [/B][/skiphigh [/LCD|/BW|/GO] [/H]
DEFRAG [d:] [/V][/B][/skiphigh] [/LCD]|/BW|/GO] [/H]
Optimizes disk performance by reorganizing the files on the disk.

DEL (ERASE)

(Internal)
DEL (ERASE) [d:][path]filename [/P]
Deletes (erases) files from disk.

DELOLDOS

(External)
DELOLDOS [/B]
Deletes all files from previous versions of DOS after a 5.0 or 6.0 installation.

DELTREE

(External)
DELTREE [/Y] [d:]path [d:]path[...]
Deletes (erases) a directory including all files and subdirectories that are in it.

DEVICE

(Internal)
DEVICE=(driver name)
Used in the CONFIG.SYS file to tell DOS which device driver to load.

DEVICEHIGH

(Internal)
DEVICEHIGH=(driver name)
Like DEVICE, DEVICEHIGH is used in the CONFIG.SYS file to tell DOS which device driver software to use for devices; however, this option is used to install the device driver into the upper memory area.

DIR

(Internal)
DIR [d:][path][filename] [/A:(attributes)] [/O:(order)] [/B][/C][/CH][/L][/S][/P][/W]
Displays directory of files and directories stored on disk.

DISKCOMP

(External)
DISKCOMP [d:] [d:][/1][/8]
Compares the contents of two diskettes.

DISKCOPY

(External)
DISKCOPY [d:] [d:][/1][/V][/M]

Makes an exact copy of a diskette.

DOS

(Internal)
DOS=[high|low],[umb|noumb]
Used in the CONFIG.SYS file to specify the memory location for DOS. It is used to load DOS into the upper memory area and to specify whether or not the upper memory blocks will be used.

DOSKEY

(External)
DOSKEY [reinstall] [/bufsize=size][/macros][/history][/insert|/overstrike] [macroname=[text]]
Loads the Doskey program into memory which can be used to recall DOS commands so that you can edit them.

DOSSHELL

(External)
DOSSHELL [/B] [/G:[resolution][n]]|[/T:[resolution][n]]
Initiates the graphic shell program using the specified screen resolution.

DRIVPARM

(Internal)
DRIVPARM= /D:(number) [/C] [/F:(form factor)] [/H:(number)] [/I][ /N][/S:(number)] [/T:(tracks)]
Used in the CONFIG.SYS file to set parameters for a disk drive.

ECHO

(Internal)
ECHO on|off
ECHO (message)
Displays messages or turns on or off the display of commands in a batch file.

EDIT

(External)
EDIT [d:][path]filename [/B][/G][/H][/NOHI]
Starts the MS-DOS editor, a text editor used to create and edit ASCII text files.

EMM386

(External)
EMM386 [on|off|auto] [w=on|off]
Enables or disables EMM386 expanded-memory support on a computer with an 80386 or higher processor.

EXE2BIN

(External)
EXE2BIN [d:][path]filename [d:][path]filename
Converts .EXE (executable) files to binary format.

EXIT

(Internal)
EXIT
Exits a secondary command processor.

EXPAND

(External)
EXPAND [d:][path]filename [[d:][path]filename[ . . .]]
Expands a compressed file.

FASTHELP

(External)
FASTHELP [command][command] /?
Displays a list of DOS commands with a brief explanation of each.

FASTOPEN

(External)
FASTOPEN d:[=n][/X]
Keeps track of the locations of files for fast access.

FC

(External)
FC [/A][/C][/L][/Lb n][/N][/T][/W][number] [d:][path]filename [d:][path]filename
or (for binary comparisons)
FC [/B][/number] [d:][path]filename [d:][path]filename
Displays the differences between two files or sets of files.

FCBS

(Internal)
FCBS=(number)
Used in the CONFIG.SYS file to specify the number of file-control blocks for file sharing.

FDISK

(External)
FDISK [/status]
Prepares a fixed disk to accept DOS files for storage.

FILES

(Internal)
FILES=(number)
Used in the CONFIG.Sys file to specify the maximum number of files that can be open at the same time.

FIND

(External)
FIND [/V][/C][/I][/N] ÒstringÓ [d:][path]filename[...]
Finds and reports the location of a specific string of text characters in one or more files.

FOR

(Internal)
FOR %%(variable) IN (set) DO (command)
or (for interactive processing)
FOR %(variable) IN (set) DO (command)

Performs repeated execution of commands (for both batch processing and interactive processing).

FORMAT

(External)
FORMAT d:[/1][/4][/8][/F:(size)] [/N:(sectors)] [/T:(tracks)][/B|/S][/C][/V:(label)] [/Q][/U][/V]
Formats a disk to accept DOS files.

GOTO

(Internal)
GOTO (label)
Causes unconditional branch to the specified label.

GRAFTABL

(External)

GRAFTABL [(code page)]
GRAFTABL [status]

Loads a table of character data into memory (for use with a color/graphics adapter).

GRAPHICS

(External)
GRAPHICS [printer type][profile] [/B][/R][/LCD][/PB:(id)] [/C][/F][/P(port)]
Provides a way to print contents of a graphics screen display.

HELP

(External)
HELP [command] [/B][/G][/H][/NOHI]
Displays information about a DOS command.

IF

(Internal)
IF [NOT] EXIST filename (command) [parameters]
IF [NOT] (string1)==(string2) (command) [parameters]
IF [NOT] ERRORLEVEL (number) (command) [parameters]
Allows for conditional operations in batch processing.

INCLUDE

(Internal)
INCLUDE= blockname
Used in the CONFIG.SYS file to allow you to use the commands from one CONFIG.SYS block within another.

INSTALL

(Internal)
INSTALL=[d: ][\path]filename [parameters]
Used in the CONFIG.SYS file to load memory-resident programs into conventional memory.

INTERLINK

(External)
INTERLINK [client[:]=[server][:]]
Connects two computers via parallel or serial ports so that the computers can share disks and printer ports.

INTERSVR

(External)
INTERSVR [d:][...][/X=d:][...] [/LPT:[n|address]] [/COM:[n|address]][/baud:rate] [/B][/V]
INTERSVR /RCOPY
Starts the Interlink server.

JOIN

(External)
JOIN d: [d:path]
JOIN d: [/D]
Allows access to the directory structure and files of a drive through a directory on a different drive.

KEYB

(External)
KEYB [xx][,][yyy][,][d:][path]filename [/E][/ID:(number)]
Loads a program that replaces the support program for U. S. keyboards.

LABEL

(External)
LABEL [d:][volume label]
Creates or changes or deletes a volume label for a disk.

LASTDRIVE

(Internal)
LASTDRIVE=(drive letter)
Used in the CONFIG.SYS file to set the maximum number of drives that can be accessed.

LOADFIX

(Internal)
LOADFIX [d:][path]filename [parameters]
Ensures that a program is loaded above the first 64K of conventional memory, and runs the program.

LOADHIGH

(Internal)
LOADHIGH (LH) [d:][path]filename [parameters]
Loads memory resident application into reserved area of memory (between 640K-1M).

MEM

(External)
MEM [/program|/debug|/classify|/free|/module(name)] [/page]
Displays amount of installed and available memory, including extended, expanded, and upper memory.

MEMMAKER

(External)
MEMMAKER [/B][/batch][/session][/swap:d] [/T][/undo][/W:size1,size2]
Starts the MemMaker program, a program that lets you optimize your computer's memory.

MENUCOLOR

(Internal)
MENUCOLOR=textcolor,[background]
Used in the CONFIG.SYS file to set the colors that will be used by DOS to display text on the screen.

MENUDEFAULT

(Internal)
MENUDEFAULT=blockname, [timeout]
Used in the CONFIG.SYS file to set the startup configuration that will be used by DOS if no key is pressed within the specified timeout period.

MENUITEM

(Internal)
MENUITEM=blockname, [menutext]
Used in the CONFIG.SYS file to create a start-up menu from which you can select a group of CONFIG.SYS commands to be processed upon reboot.

MIRROR

(External)
MIRROR [d:]path [d:] path [...]
MIRROR [d1:][d2:][...] [/T(drive)(files)] [/partn][/U][/1]
Saves disk storage information that can be used to recover accidentally erased files.

MKDIR

(MD) (Internal)
MKDIR (MD) [d:]path
Creates a new subdirectory.

MODE

(External)
MODE n
MODE LPT#[:][n][,][m][,][P][retry]
MODE [n],m[,T]
MODE (displaytype,linetotal)
MODE COMn[:]baud[,][parity][,][databits][,][stopbits][,][retry]
MODE LPT#[:]=COMn [retry]
MODE CON[RATE=(number)][DELAY=(number)]
MODE (device) CODEPAGE PREPARE=(codepage) [d:][path]filename
MODE (device) CODEPAGE PREPARE=(codepage list) [d:][path]filename
MODE (device) CODEPAGE SELECT=(codepage)
MODE (device) CODEPAGE [/STATUS]
MODE (device) CODEPAGE REFRESH
Sets mode of operation for devices or communications.

MORE

(External)
MORE < (filename or command)
(name)|MORE
Sends output to console, one screen at a time.
MOVE

(Internal)
MOVE [/Y|/-Y] [d:][path]filename[,[d:][path]filename[...]] destination
Moves one or more files to the location you specify. Can also be used to rename directories.
MSAV

(External)
MSAV [d:] [/S|/C][/R][/A][/L][/N][/P][/F][/video][/mouse]
MSAV /video
Scans your computer for known viruses.
MSBACKUP

(External)
MSBACKUP [setupfile] [/BW|/LCD|/MDA]
Used to backup or restore one or more files from one disk to another.
MSCDEX

(External)
MSCDEX /D:driver [/D:driver2. . .] [/E][/K][/S][/V][/L:letter] [/M:number]
Used to gain access to CD-ROM drives (new with DOS Version 6).
MSD

(External)
MSD [/B][/I]
MSD [/I] [/F[d:][path]filename [/P[d:][path]filename [/S[d:][path]filename
Provides detailed technical information about your computer.
NLSFUNC

(External)
NLSFUNC [d:][path]filename
Used to load a file with country-specific information.

NUMLOCK

(Internal)
NUMLOCK=on|off
Used in the CONFIG.SYS file to specify the state of the NumLock key.
PATH

(Internal)
PATH;
PATH [d:]path[;][d:]path[...]
Sets or displays directories that will be searched for programs not in the current directory.
PAUSE

(Internal)
PAUSE [comment]
Suspends execution of a batch file until a key is pressed.
POWER

(External)
POWER [adv:max|reg|min]|std|off]
Used to turn power management on and off, report the status of power management, and set levels of power conservation.
PRINT

(External)
PRINT [/B:(buffersize)] [/D:(device)] [/M:(maxtick)] [/Q:(value] [/S:(timeslice)][/U:(busytick)] [/C][/P][/T] [d:][path][filename] [...]
Queues and prints data files.
PROMPT

(Internal)
PROMPT [prompt text] [options]
Changes the DOS command prompt.
RECOVER

(External)
RECOVER [d:][path]filename
RECOVER d:
Resolves sector problems on a file or a disk. (Beginning with DOS Version 6, RECOVER is no longer available ).
REM

(Internal)
REM [comment]
Used in batch files and in the CONFIG.SYS file to insert remarks (that will not be acted on).
RENAME (REN)

(Internal)
RENAME (REN) [d:][path]filename [d:][path]filename
Changes the filename under which a file is stored.
REPLACE

(External)
REPLACE [d:][path]filename [d:][path] [/A][/P][/R][/S][/U][/W]
Replaces stored files with files of the same name from a different storage location.

RESTORE

(External)
RESTORE d: [d:][path]filename [/P][/S][/B:mm-dd-yy] [/A:mm-dd-yy][/E:hh:mm:ss] [/L:hh:mm:ss] [/M][/N][/D]
Restores to standard disk storage format files previously stored using the BACKUP command.
RMDIR (RD)

(Internal)
RMDIR (RD) [d:]path
Removes a subdirectory.
SCANDISK

(External)
SCANDISK [d: [d: . . .]|/all][/checkonly|/autofix[/nosave]|/custom][/surface][/mono][/nosummay]
SCANDISK volume-name[/checkonly|/autofix[/nosave]|/custom][/mono][/nosummary]
SCANDISK /fragment [d:][path]filename
SCANDISK /undo [undo-d:][/mono]
Starts the Microsoft ScanDisk program which is a disk analysis and repair tool used to check a drive for errors and correct any problems that it finds.
SELECT

(External)
SELECT [d:] [d:][path] [country code][keyboard code]
Formats a disk and installs country-specific information and keyboard codes (starting with DOS Version 6, this command is no longer available).
SET

(Internal)
SET (string1)=(string2)
Inserts strings into the command environment. The set values can be used later by programs.

SETVER

(External)
SETVER [d:]:path][filename (number)][/delete][/quiet]
Displays the version table and sets the version of DOS that is reported to programs.
SHARE

(External)
SHARE [/F:space] [/L:locks]
Installs support for file sharing and file locking.
SHELL

(Internal)
SHELL=[d:][path]filename [parameters]
Used in the CONFIG.SYS file to specify the command interpreter that DOS should use.
SHIFT

(Internal)
SHIFT
Increases number of replaceable parameters to more than the standard ten for use in batch files.
SORT

(External)
SORT [/R][/+n] < (filename)
SORT [/R][/+n] > (filename2)

Sorts input and sends it to the screen or to a file.
STACKS

(Internal)
STACKS=(number),(size)
Used in the CONFIG.SYS file to set the number of stack frames and the size of each stack frame.
SUBMENU

(Internal)
SUBMENU=blockname, [menutext]
Used in the CONFIG.SYS file to create a multilevel menu from which you can select start-up options.
SUBST

(External)
SUBST d: d:path
SUBST d: /D
Substitutes a virtual drive letter for a path designation.
SWITCHES

(Internal)
SWITCHES= [/K][/F][/N][/W]
Used in the CONFIG.SYS file to configure DOS in a special way; for example, to tell DOS to emulate different hardware configurations.
SYS

(External)
SYS [source] d:
Transfers the operating system files to another disk.
TIME

(Internal)
TIME hh:mm[:ss][.cc][A|P]
Displays current time setting of system clock and provides a way for you to reset the time.
TREE

(External)
TREE [d:][path] [/A][/F]
Displays directory paths and (optionally) files in each subdirectory.
TYPE

(Internal)
TYPE [d:][path]filename
Displays the contents of a file.
UNDELETE

(External)
UNDELETE [d:][path][filename] [/DT|/DS|/DOS]
UNDELETE [/list|/all|/purge[d:]|/status|/load|/U|/S[d:]|/Td:[-entries]]
Restores files deleted with the DELETE command.
UNFORMAT

(External)
UNFORMAT d: [/J][/L][/test][/partn][/P][/U]
Used to undo the effects of formatting a disk.
VER

(Internal)
VER
Displays the DOS version number.
VERIFY

(Internal)
VERIFY on|off
Turns on the verify mode; the program checks all copying operations to assure that files are copied correctly.
VOL

(Internal)
VOL [d:]
Displays a disk's volume label.
VSAFE

(External)
VSAFE [/option[+|-]...] [/NE][/NX][Ax|/Cx] [/N][/D][/U]
VSAFE is a memory-resident program that continuously monitors your computer for viruses and displays a warning when it finds one.
XCOPY

(External)
XCOPY [d:][path]filename [d:][path][filename] [/A][/D:(date)] [/E][/M][/P][/S][/V][/W][Y\-Y]
Copies directories, subdirectories, and files.