Operating Systems: Process Management

• An operating system (OS) is system software that manages computer hardware and software resources and provides common services for computer programs
• It acts as an intermediary between the user and the hardware, managing resources like the CPU, memory, storage, and peripherals

Process Management

• A process is an instance of a computer program that is being executed
• Process management involves creating, scheduling, and terminating processes
• The OS assigns resources to processes, allowing them to execute
• Key aspects include process scheduling, inter-process communication, and synchronization
  • Process scheduling determines which process gets to run on the CPU and for how long
  • Scheduling algorithms include First-Come, First-Served (FCFS), Shortest Job First (SJF), Priority Scheduling, and Round Robin
  • Inter-Process Communication (IPC) refers to the mechanisms by which processes can communicate with each other
  • Common IPC methods include message passing and shared memory
  • Synchronization ensures that multiple processes can access shared resources without creating data inconsistencies
  • Mechanisms for synchronization include mutexes, semaphores, and monitors
• Process States: A process can be in one of several states, such as new, ready, running, waiting/blocked, or terminated

Memory Management

• Memory management is the function of the OS that manages the computer's main memory
• Main memory is a resource that must be allocated and deallocated to processes
• Memory management techniques include:
  • Allocation which involves assigning memory space to different programs or processes
  • Processes request memory, the OS allocates available memory blocks
  • Deallocation releases previously allocated memory blocks when they are no longer needed
  • Efficient allocation and deallocation prevent memory leaks and fragmentation
• Virtual memory is a technique that allows processes to execute even if they are not entirely in memory
• It creates the illusion of a larger address space by using disk space as an extension of RAM
• Paging and segmentation are virtual memory techniques
  • Paging divides memory into fixed-size blocks called pages
  • Segmentation divides memory into variable-size blocks called segments
• Address translation maps virtual addresses to physical addresses
• Page tables are used to store the mapping between virtual pages and physical frames
• Memory protection ensures that processes can only access memory locations that are allocated to them
• This prevents processes from interfering with each other's memory space

File Systems

• A file system is a method of organizing and storing files on a storage device
• It provides a way to manage files and directories (folders)
• Key functions of a file system include:
  • Directory management which involves creating, deleting, and organizing directories
  • File allocation which involves allocating storage space to files, usually in contiguous blocks
  • Naming conventions which are rules for naming files and directories
  • Metadata management which involves storing information about files, such as their size, creation date, and permissions
• Common file systems include FAT32, NTFS, ext4, and APFS
  • FAT32 is an older file system that is widely compatible with various operating systems
  • NTFS (New Technology File System) is the standard file system for Windows
  • ext4 is a journaling file system commonly used in Linux
  • APFS (Apple File System) is the default file system for macOS
• File access methods include sequential access, random access, and indexed sequential access
• File permissions control who can access a file and what they can do with it
• Typical permissions include read, write, and execute
• File system integrity is maintained through techniques like journaling, which records changes to the file system before they are made

Security and Access Control

• Security in operating systems refers to mechanisms that protect the system and user data from unauthorized access and malicious activities
• Access control mechanisms determine who can access system resources and what they can do with them
• Authentication verifies the identity of users, commonly through passwords, biometrics, or multi-factor authentication
• Authorization determines what resources a user can access after they have been authenticated
• Access control lists (ACLs) specify permissions for each user or group of users
• Role-Based Access Control (RBAC) assigns permissions based on the roles that users have within an organization
• Security threats include malware, viruses, worms, and trojan horses
• Firewalls are used to block unauthorized network access
• Intrusion detection systems (IDS) monitor network traffic for suspicious activity
• Encryption protects data by encoding it so that it can only be read by authorized users
  • Encryption can be used to protect data at rest (stored data) and data in transit (data being transmitted over a network)
• Security policies define the rules and procedures for maintaining a secure computing environment
• Regular security audits help to identify vulnerabilities and ensure that security policies are being followed

System Calls

• System calls are the interface between user-level processes and the OS kernel
• They allow user programs to request services from the OS, such as file I/O, memory allocation, and process creation
• System calls are typically invoked through a software interrupt
• The OS kernel handles the system call and returns the result to the user process
• Examples of system calls include:
  • read() and write(): Used for file I/O
  • malloc() and free(): Used for memory allocation
  • fork() and exec(): Used for process creation
  • open() and close(): Used for file management
• System call interface provides a layer of abstraction that protects the OS kernel from user-level programs
• It ensures that user programs cannot directly access or modify kernel data structures
• System calls are essential for building a wide range of applications, from simple command-line tools to complex graphical user interfaces
• The implementation of system calls varies from one OS to another
• However, the basic principles remain the same: user programs request services from the OS kernel through a well-defined interface