Operating System: Process Management

• An operating system (OS) manages computer hardware and software resources and provides common services for computer programs
• It acts as an intermediary between the user and the hardware

Process Management

• Process management involves creating, scheduling, and terminating processes
• A process is an instance of a computer program that is being executed
• Process scheduling algorithms determine which process will be executed by the CPU
• Common scheduling algorithms include First-Come, First-Served (FCFS), Shortest Job First (SJF), Priority Scheduling, and Round Robin
• FCFS executes processes in the order they arrive
• SJF executes the process with the shortest execution time first
• Priority scheduling executes processes based on assigned priorities
• Round Robin allocates a fixed time slice to each process
• Inter-process communication (IPC) enables processes to exchange data and synchronize execution
• Common IPC mechanisms include shared memory, message passing, and pipes
• Process synchronization ensures that multiple processes access shared resources in a controlled manner to prevent data inconsistency
• Synchronization mechanisms include mutex locks, semaphores, and monitors
• Deadlock occurs when two or more processes are blocked indefinitely, waiting for each other

Memory Management

• Memory management allocates and deallocates memory space to programs
• The goal is to efficiently utilize memory and prevent processes from interfering with each other
• Virtual memory allows a process to access more memory than is physically available
• It uses techniques like paging and segmentation to map virtual addresses to physical addresses
• Paging divides memory into fixed-size blocks called pages
• Segmentation divides memory into variable-size blocks called segments
• Page replacement algorithms are used to decide which page to evict from memory when a new page needs to be loaded
• Common page replacement algorithms include FIFO (First-In, First-Out), LRU (Least Recently Used), and Optimal
• Memory fragmentation occurs when memory is allocated and deallocated over time, leading to unused memory gaps
• Fragmentation can be internal (within a partition) or external (between partitions)
• Compaction is a technique used to reduce external fragmentation by moving allocated memory blocks to contiguous locations

File Systems

• A file system organizes and manages files on storage devices
• It provides a hierarchical structure of directories (folders) and files
• File systems define how data is stored, accessed, and retrieved
• Common file system operations include creating, reading, writing, and deleting files
• Different file systems have different characteristics, such as maximum file size, filename length, and supported features
• Examples of file systems include FAT32, NTFS, ext4, and APFS
• File system metadata stores information about files, such as name, size, permissions, and timestamps
• Access control mechanisms regulate who can access and modify files
• File system security features include permissions, access control lists (ACLs), and encryption
• Disk scheduling algorithms optimize the order in which disk I/O requests are serviced
• Common disk scheduling algorithms include FCFS, SSTF (Shortest Seek Time First), SCAN, and C-SCAN

Security in OS

• OS security protects the system from unauthorized access, malware, and other threats
• User authentication verifies the identity of users trying to access the system
• Common authentication methods include passwords, biometrics, and multi-factor authentication
• Access control mechanisms restrict users' access to system resources based on their roles and permissions
• Privilege escalation occurs when a user gains unauthorized access to higher-level privileges
• Security policies define the rules and guidelines for maintaining system security
• Firewalls protect the system by filtering network traffic and blocking malicious connections
• Intrusion detection systems (IDS) monitor the system for suspicious activity and alert administrators
• Antivirus software detects and removes malware from the system
• Encryption protects data confidentiality by converting it into an unreadable format
• Security vulnerabilities are weaknesses in the system that can be exploited by attackers
• Regular security updates and patches are essential to address vulnerabilities

System Calls

• System calls are the interface between user-level programs and the OS kernel
• User programs request services from the OS kernel through system calls
• System calls provide access to hardware resources and privileged operations
• Examples of system calls include file I/O, memory allocation, process creation, and network communication
• When a user program makes a system call, the OS kernel takes over and performs the requested operation
• System call handling involves switching from user mode to kernel mode
• System calls are typically implemented using a software interrupt or trap
• The system call interface provides a level of abstraction, shielding user programs from the complexities of the underlying hardware
• Different operating systems have different system call interfaces
• System call overhead can impact performance, so it's important to minimize the number of system calls