Which command is used to list files in DOS?

An Operating System (OS) is system software that manages computer hardware and software resources. Main functions: Process Management, Memory Management, File System Management, I/O Management, Security, and User Interface. Common OS: Windows (Microsoft), macOS (Apple), Linux/Ubuntu (open-source), Android and iOS (mobile). OS is an important topic in Computer Awareness for SSC, IBPS Bank, and Railway exams.

Types of Operating Systems: Batch OS (processes jobs in batches without user interaction), Time-Sharing OS (multiple users share computer time, UNIX), Real-Time OS (used in embedded systems, RTOS), Network OS (manages network resources, Windows Server), Distributed OS (manages group of computers as a single system), and Mobile OS (Android, iOS). Windows, Linux, and macOS are the most common desktop operating systems.

Process Management handles creation, scheduling, and termination of processes. A process is a program in execution. Process states: New, Ready, Running, Waiting, Terminated. Process Scheduling algorithms: FCFS (First Come First Serve), SJF (Shortest Job First), Round Robin (time quantum based), Priority Scheduling. The OS uses PCB (Process Control Block) to store process information. Deadlock is when two processes wait for each other's resources.

Memory Management allocates and deallocates memory for processes. Techniques: Paging (divides memory into fixed-size pages), Segmentation (divides into variable-size segments), Virtual Memory (uses disk space as extended RAM), and Swapping (moves processes between RAM and disk). Internal fragmentation occurs with paging; external fragmentation occurs with variable partitions.

A Process is an independent program in execution with its own memory space and resources. Processes are isolated from each other. A Thread is the smallest unit of execution within a process. Threads within the same process share memory space and resources. Multi-threading allows concurrent execution within a process. Threads are lighter than processes with faster context switching.