MS-DOS Commands PDF

4)Segmentation in operating system Segmentation is a memory management technique in which each job is divided into several segments of different sizes, one for each module that contains pieces that perform related functions. Each segment is actually a different logical address space of the program....

4)Segmentation in operating system Segmentation is a memory management technique in which each job is divided into several segments of different sizes, one for each module that contains pieces that perform related functions. Each segment is actually a different logical address space of the program. When a process is to be executed, its corresponding segmentation are loaded into non-contiguous memory though every segment is loaded into a contiguous block of available memory. Segmentation memory management works very similar to paging but here segments are of variable-length where as in paging pages are of fixed size. A program segment contains the program\'s main function, utility functions, data structures, and so on. The operating system maintains a **segment map table** for every process and a list of free memory blocks along with segment numbers, their size and corresponding memory locations in main memory. For each segment, the table stores the starting address of the segment and the length of the segment. A reference to a memory location includes a value that identifies a segment and an offset. Segment table - - **Advantages of segmentation** - It reduces memory usage. - Page table size is limited by the segment size. - Segment table has only one entry corresponding to one actual segment. - External Fragmentation is not there. - It simplifies memory allocation. 1. Disk Operating System (DOS) commands A disk operating system (DOS) is a type of computer software that helps manage files and data stored on a computer\'s disk drive. It is like the traffic cop for a computer\'s hard drive, organizing and directing the flow of information. DOS used to be the primary operating system used on older computers, but nowadays it is mostly used for specific tasks or for troubleshooting older systems. Advantages of using Disk Operating System (DOS) We use disk operating systems (DOS) for several reasons, including − - **File management** − **DOS** provides a command-line interface for managing files and directories on a disk storage device. It allows users to **copy, move, rename, delete,** and **view files** and **directories**. - **Program execution** − **DOS** allows users to execute programs or applications directly from the command line. This was an important feature in the early days of computing when **graphical user interfaces (GUIs)** were not yet widely available. - **Troubleshooting and system maintenance** − **DOS** can be used for troubleshooting and repairing issues on older systems, as it provides a **low-level interface** to the hardware and file system. - **Learning computing basics** − Learning **DOS commands** is a good way to understand the basics of computing, including file systems, operating systems, and programming. Types of DOS Commands - **Internal Commands** − Internal commands are the commands that are built into the command interpreter or the command prompt of the DOS operating system. These commands do not require a separate executable file to run and can be used directly from the command prompt. - **External Commands** − External commands in DOS are commands that are not built into the command interpreter, but are separate executable files that need to be located in the system\'s path or directory to be executed from the command prompt. External commands are usually more complex and are used for more advanced tasks than internal commands. Internal DOS Commands Internal or Basic DOS commands are simple and essential commands that users can use to interact with the file system and execute simple tasks. Here are some examples of basic DOS commands − - **DIR** − Displays a list of files and directories in the current directory. - **CD** − Changes the current directory to a specified directory. - **MD** − Creates a new directory. - **RD** − Removes an empty directory. - **COPY** − Copies a file from one location to another. - **DEL** − Deletes a file. - **REN** − Renames a file or directory. - **TYPE** − Displays the contents of a text file. - **VER** − Displays the version number of the operating system. - **DATE** − Displays or sets the system date. - **TIME** − Displays or sets the system time. - **CLS** − Clears the screen. - **PROMPT** − Change the command prompt. - **TREE** − Displays a graphical representation of the directory structure. - **FC** − Compares two files or sets of files and displays the differences between them. - **SHIFT** − Changes the position of command line arguments. - **SORT** − Sorts the contents of a file alphabetically or numerically. - **BREAK** − Controls the handling of extended keyboard CTRL+C and CTRL+BREAK input. External DOS Commands - **ATTR** − Displays or changes file attributes. - **COMMAND** − Starts a new instance of the command interpreter. - **DRIVERQUERY** − Displays a list of installed device drivers. - **EVENTCREATE** − Writes an entry to the application event log. - **EXIT** − Exits the command interpreter or batch script. - **HELP** − Provides help information for Windows commands. - **OPENFILES** − Displays information about open files and the users who opened them. - **SHUTDOWN** − Shut down or restart the local or remote computer.