Neon-komputadór

MS-DOS and NTVDM

Microsoft DOS (Disk Operating System) is a command line user interface. MS-DOS 1.0 was released in 1981 for IBM computers and the latest version of MS-DOS is MS-DOS 6.22 released in 1994. While MS-DOS is rarely used by itself today, it still can be accessed from the various Windows platforms from Start -> Programs -> Accessories -> Command Prompt. In the default Windows XP menu, it is Start -> All Programs -> Accessories -> Command Prompt. The following commands applies for MS-DOS 6.2x. As mentioned in previous chapters, in MS-Windows 95, MS-Windows 98 and MS-Windows ME, the Windows GUI operates on top of the MS-DOS operating system whereas in MS-Windows NT, MS-Windows 2000 and MS-Windows XP a virtual DOS machines is used instead.

When MS-DOS is opened, the command prompt line provides the current drive and directory (for example: C:\Documents and Settings\Lev Lafayette>). MS-DOS organizes the directory structure according to drives, rather than placing all files and devices under a single root directory. By default, the a:\ drive represents the floppy disk, the b:\ any additional floppy disks, the c:\ drive the first hard disk and any additional hard disks or cd-rom drives are usually found at d:\ or e:\ and so forth. The directory structure however will vary according to what version of Windows is being used. In Windows XP, there are only three main directories, c:\windows, c:\Documents and Settings and c:\Program Files.

Commands are entered on the current command line with drives, paths and filenames following if applicable and any switches as desired by the user. The basic directory manipulation commands are as follows: 'dir' to give a listing of files and subdirectories the directory, 'cd' or 'chdir' to change directory or display the current directory name, 'md' or 'mkdir' to make a new directory or subdirectory, and 'rd' or 'rmdir' to remove an empty directory, Useful switches in directory display include 'dir /w', to give a wide column display, 'dir/o:?', to give a sorted listed (where '?' is either N (alphabetic name), E (by alphabetic extension), G (group directories first), S (by size, smallest to largest) and D (by age, oldest first) and 'dir /a:?', which displays by specified attributes (where '?' is D (directories), H (hidden files), S (system files), R (read only files). For directory changes the command 'cd ..' changes the current directory to the parent directory. For creating directories, the command can create any intermediate directories, so if the command 'mkdir \a\b\c\d' is entered it is the equivalent of typing 'mkdir \a', 'chdir \a', 'mkdir \b', chdir \b', 'mkdir \c', 'chdir \c', 'mkdir \d'. For removing directories the switch '/s' removes all subdirectories and files in the specified directory and the '/q' carries this out without confirmation. The latter switch in particular is not recommended.

The main file manipulation commands are 'copy', which copies one or more files to a specified location, 'xcopy'. which copies files and subdirectories, 'del' or 'erase', which deletes one or more files, 'move', which moves one or more files to a new location, 'ren' or 'rename' to rename one or more files, 'verify' to check whether files have been correctly written to a disk, 'more' to display the contents of a file, 'print' to print a text file, 'find' or 'findstr' to search for a text string in a file or files, 'fc' to compare and display the differences of any two files, 'sort' to sort an input file, 'attrib' to display or change file attributes and 'edit' to open a simple text editor. The use of the wildcards '?' and '*' is allowed throughout file manipulation commands. The most useful switch for copy and xcopy is '/V' which verifies that files have been written correctly.

Other useful switches in xcopy include '/EXCLUDE:file1+file2+file3' etc, which excludes the specified files, '/c', which continues to copy files ever if interrupted by an error, '/h' which copies hidden and system files as well, '/r' which overwrites read-only files and '/t' that copies the directory structure, but not the files, The most useful switches for deleting or erasing files are '/f', which forces the deletion of read-only files and /a:? which deletes according to attribute (where '?' is the particular attribute, 'r' for read-only, 's' for 'system', 'h' for hidden). Use of the '/q', quite switch, which suppresses prompts when using a global wildards for deletion is not recommended. For the 'find' command the most useful switches are '/v', which displays the lines which do not contain the specified string and '/n' which displays the line numbers. Note that with find, the syntax is 'find switches string drive directory filename'. 'Findstr' is a more powerful version of 'find' and includes additional switches, such as the ability to find a switch at the beginning of a line ('/b') at the end of a line (/'e) among others. The syntax is the same.

Disk manipulation commands include 'format' to format a disk, 'diskcomp' and 'diskcopy' which compares the contents of two floppy disks and copies the contents of one floppy disk to another, 'covert' to change a FAT file system to NTFS (but not the disk that is currently been worked on), 'chkdsk' to check and display a status report of a disk, and 'vol' to display a disk volume label and serial number. Useful system commands include 'at', which runs a command at a particular time, 'date' and 'time', which displays or changes the system's date and time, 'exit' to close the MS-DOS session, 'cls' to clear the screen, 'prompt' to change the command prompt, and the ever useful 'help' command. There are also a number of commands which are mainly used in the creation of batch files, which are a sequence of commands that can executed as a single action. These include 'echo', which displays a message, 'for', which runs a command for each file in a set of files, 'if', which establishes conditional responses, Batch files will be discussed in greater detail on the Chapter V.