What is a file descriptor?

Interrupt requests (IRQs) are signals sent to the CPU indicating that a device needs attention. IRQs help manage hardware communication and prioritize tasks. For instance, pressing a key on the keyboard generates an IRQ to notify the OS to read the keystroke.

A file system manages the storage and retrieval of files on a disk. It organizes files into directories and handles metadata such as file size and permissions. For example, NTFS in Windows and ext4 in Linux are file systems that manage data storage and access.

Virtual memory is a memory management technique that creates an illusion of a larger physical memory by using disk space. It allows for more efficient memory utilization and process isolation. For example, a system with 4GB RAM can use virtual memory to handle more data by paging to disk.

Paging is a memory management scheme that eliminates the need for contiguous allocation of physical memory. It divides memory into fixed-size pages and maps them to physical memory frames. This allows for efficient and flexible memory use, as pages can be loaded and swapped as needed.

Deadlock occurs when two or more processes are stuck in a state where each is waiting for the other to release resources, causing none to proceed. For instance, if two processes are each holding a lock and waiting for the other to release its lock, neither can continue.

A program is a static set of instructions stored on disk, whereas a process is a dynamic entity that executes the program's instructions. A program becomes a process when it is loaded into memory and executed. For example, a word processor application (program) runs as a process when opened.

A race condition occurs when the outcome of a process depends on the sequence or timing of uncontrollable events. It can lead to unpredictable results. To prevent race conditions, synchronization mechanisms like mutexes and semaphores are used to ensure orderly access to shared resources.

Context switching is the process of saving the state of a currently running process and loading the state of the next process to be executed. It involves saving registers, program counter, and other context information. For example, switching between multiple applications on a computer involves context switching.

A file descriptor is an integer handle used by the OS to access files and I/O resources. It is returned by system calls like 'open' and used in subsequent operations such as 'read' or 'write'. For example, in Unix-like systems, file descriptor 0 refers to standard input.

A process is an independent program in execution, while a thread is a smaller unit of a process that can run concurrently. Threads share resources of the process but have their own execution path. For example, a web browser (process) might have multiple tabs (threads) running simultaneously.

A semaphore is a synchronization primitive used to control access to shared resources by multiple processes. It consists of a counter and operations (wait and signal) to manage resource allocation. For example, semaphores can prevent race conditions in concurrent programming by ensuring mutual exclusion.