Essential Operating System Concepts: A Comprehensive Glossary

Operating System (OS)

: A system that manages computer hardware and software resources, acting as the kernel and foundation for tasks such as memory management, resource scheduling, I/O control, and providing a user interface.

Shell

: A program that receives commands from the keyboard and passes them to the OS for execution; historically the only interface on Unix-like systems, now complemented by graphical user interfaces (GUI).

Graphical User Interface (GUI)

: A user interface that allows interaction with electronic devices through graphical icons and audio cues.

Kernel Mode (Supervisior Mode)

: The privileged execution mode where code has unrestricted access to hardware, can execute any CPU instruction, and reference any memory address; crashes in this mode are catastrophic. User Mode: The mode in which the OS runs user applications; transitions to kernel mode occur via system calls, interrupts, or faults. Computer Architecture: The set of rules and methods describing a computer system's functionality, organization, and implementation, including instruction sets, memory management, I/O, and bus structures.

SATA (Serial ATA)

: A serial bus that transfers data between the motherboard and large storage devices such as hard drives and optical drives. Multiplexing: The sharing of resources in time or space, allowing multiple programs or users to use a resource in turn. Mainframes: Large computers known for size, storage capacity, processing power, and high reliability, typically used for critical data‑processing tasks.

Batch System

: An OS where users submit jobs via offline devices; the system groups similar jobs and runs them together without direct user interaction. OS/360: IBM's discontinued batch operating system for the System/360 mainframe, released in 1964. Multitasking: The ability of a computer to run multiple programs concurrently by saving and restoring each program's state. Time‑Sharing: A system that allows many users to share computing resources simultaneously through multiple programs and tasks. Compatible Time‑Sharing System (CTSS): The earliest time‑sharing OS, designed and implemented at MIT's Computation Center. Cloud Computing: On‑demand availability of computing resources such as storage and processing power over the Internet, often delivered from distributed data centers.

UNIX

: A powerful multi‑user, multitasking OS supporting multiple processor architectures; classified as a time‑sharing system. UNIX System V: A branch of the UNIX operating system. BSD (Berkeley Software Distribution): A derivative of UNIX. POSIX: A set of IEEE standards defining portable OS interfaces for UNIX-like systems. MINIX: A miniature UNIX‑like operating system. Linux: A widely used, open‑source UNIX‑like operating system.

DOS (Disk Operating System)

: An OS that uses disk storage devices such as floppy disks, hard drives, or optical discs. MS‑DOS: Microsoft’s widely used DOS for Intel x86 PCs, dominant before Windows 95.

macOS

: Apple’s GUI‑based operating system for Macintosh computers.

Windows NT

: Microsoft’s pure 32‑bit operating system kernel introduced in 1993. Service Pack (SP): A collection of updates, fixes, and enhancements released as a single installable package. DRM (Digital Rights Management): Technologies that restrict the use of copyrighted hardware and software. x86: An instruction‑set architecture originally based on Intel 8086/8088, with 32‑bit default and a 64‑bit extension (x86‑64). FreeBSD: A UNIX‑like operating system developed by the FreeBSD project. X Window System: A bitmap display window system commonly used on UNIX‑like OSes.

GNOME

: A fully free desktop environment primarily targeting Linux, also supported on many BSD systems.

Network Operating System (NOS)

: An OS designed for network devices such as routers, switches, or firewalls.

Distributed Operating System

: Software that runs on a collection of independent, network‑connected computing nodes, providing a global OS view.

Program Counter

: A CPU register that indicates the position of the next instruction to execute. Stack Pointer: A CPU register that tracks the call stack. Program Status Word: An OS‑maintained data collection (8‑byte or 64‑bit) that tracks the current system state. Pipeline: A series of data‑processing elements where the output of one element is the input of the next, often executed in parallel or time‑sliced.

Superscalar

: A CPU architecture that enables instruction‑level parallelism within a single core, increasing throughput at the same clock speed. System Call: A request from a user‑space program to the OS kernel for a privileged service, such as I/O or inter‑process communication. Multithreading: The technique of executing multiple threads concurrently, either via hardware support or software scheduling, to improve overall performance. CPU Core: The processing unit of a CPU that fetches, decodes, and executes instructions; a CPU may contain multiple cores. GPU (Graphics Processing Unit): A specialized processor for rendering graphics, also used for parallel computation in PCs, workstations, game consoles, and mobile devices.

Cache Hierarchy

: A multi‑level storage structure where upper levels (L1, L2, L3) are faster but smaller, and lower levels are larger but slower. Cache Line: A fixed‑size block of data transferred between memory and cache. Cache Hit: When a requested data item is found in the cache, avoiding a slower memory access.

L1 Cache

: The fastest, smallest cache located on the CPU die, also called the primary cache. L2 Cache: A secondary cache that stores data for the L1 cache; slower than L1 but larger. L3 Cache: A tertiary cache, often on the motherboard or CPU module, providing data to L2. RAM (Random Access Memory): Volatile main memory that the CPU can read from and write to directly; used for temporary storage of programs, data, and intermediate results. ROM (Read‑Only Memory): Non‑volatile memory that retains data without power and cannot be altered after manufacturing. EEPROM: Electrically erasable programmable read‑only memory that can be rewritten multiple times. Flash Memory: A type of EEPROM used for general‑purpose data storage and removable media such as USB drives. SSD (Solid State Drive): A storage device that uses flash memory instead of spinning magnetic disks.

Virtual Memory

: A memory‑management technique that gives applications the illusion of a contiguous address space, using both physical RAM and disk storage. MMU (Memory Management Unit): Hardware that translates virtual addresses to physical addresses, provides memory protection, and controls CPU caches.

Context Switch

: The mechanism of saving the state of a running process and restoring the state of another, enabling multitasking. Device Driver: Software that provides an interface between high‑level applications and hardware devices, allowing data exchange.

Busy Waiting (Spin)

: A loop that repeatedly checks a condition, often used for checking keyboard input or lock availability. Interrupt: An asynchronous signal from hardware or a synchronous signal from software that causes the CPU to pause current execution and handle the event. Interrupt Vector: An entry in the interrupt vector table that points to the address of an interrupt handler.

DMA (Direct Memory Access)

: A technique that allows hardware subsystems to read/write system memory without CPU intervention. Bus: A standardized communication pathway that transfers data between computer components. PCIe (Peripheral Component Interconnect Express): A high‑speed serial bus standard derived from PCI, used for connecting peripherals. DMI (Direct Media Interface): Intel’s proprietary bus linking the northbridge and southbridge chips on a motherboard. USB (Universal Serial Bus): A serial bus and I/O standard for connecting computers to external devices, widely used in PCs, mobile devices, cameras, and game consoles.

BIOS (Basic Input Output System)

: Firmware that initializes hardware during boot and provides runtime services to the OS.

Hard Real‑Time System

: A system that must meet every deadline, used in critical applications such as nuclear control, medical devices, defense, and avionics. Soft Real‑Time System: A system that can miss some deadlines without catastrophic failure, e.g., audio playback in computers. Process: The executing instance of a program, containing its own memory space and resources. Address Space: The range of valid memory addresses that a process can use, which may be physical or virtual. Process Table: The OS‑maintained data structure holding information about each process, such as ID, state, priority, registers, and pending signals. Command‑Line Interpreter: The text‑based interface used before GUIs became common, where users type commands via the keyboard.

Interprocess Communication (IPC)

: Techniques that allow two or more processes or threads to exchange data or signals. Superuser: A privileged account (e.g., root, administrator) used for system management. Directory: A virtual container in a file system that holds files and other directories. Path Name: A textual representation that uniquely identifies a file or directory location in a file system. Root Directory: The top‑most directory in a file system hierarchy (e.g., C:\ on Windows, / on Linux). Working Directory: The current directory in which a user or process operates, used for relative file access. File Descriptor: An abstract handle used by programs to refer to an open file or I/O resource. Inode: A data structure in UNIX systems that stores metadata about a file, such as ownership, permissions, and location. Shared Library: A file containing compiled code that can be used by multiple executable files at runtime. DLL (Dynamic‑Link Library): Microsoft’s implementation of shared libraries, with extensions .dll, .ocx, or .drv. Client: A computer or software that requests services from a server. Server: A program or device that provides services to clients. Client‑Server Architecture: A network model that separates responsibilities between clients and servers (also called C/S).

Virtual Machine (VM)

: Software that creates an abstracted environment between the physical hardware and the user, allowing other software to run within that environment.

Java Virtual Machine (JVM)

: An abstract computing machine that executes Java bytecode, providing platform independence. Object File: A file containing machine code that is not directly executable; it must be linked to produce an executable or shared library. C Preprocessor: A tool that processes C/C++ source files before compilation, handling includes, macro expansion, conditional compilation, and line control.

References:

https://blog.csdn.net/zhangjg_blog/article/details/20380971

https://www.techopedia.com/definition/4763/address-space

https://en.wikipedia.org/wiki/Direct_Media_Interface

https://en.wikipedia.org/wiki/Bus_(computing)

https://en.wikipedia.org/wiki/Interrupt_vector_table

https://en.wikipedia.org/wiki/Busy_waiting

https://en.wikipedia.org/wiki/Context_switch

https://en.wikipedia.org/wiki/Read-only_memory

https://www.techopedia.com/definition/6306/cache-hit

https://zhuanlan.zhihu.com/p/37749443

https://en.wikipedia.org/wiki/Pipeline_(computing)

https://en.wikipedia.org/wiki/Stack_register

https://en.wikipedia.org/wiki/Distributed_operating_system

https://en.wikipedia.org/wiki/Time-sharing

https://zh.wikipedia.org/wiki/UNIX

https://zh.wikipedia.org/wiki/UNIX_System_V

https://en.wikipedia.org/wiki/Network_operating_system

https://zh.wikipedia.org/zh/X86-64

https://zh.wikipedia.org/zh/X86

https://en.wikipedia.org/wiki/Cloud_computing

https://www.techopedia.com/definition/24356/mainframe

https://zh.wikipedia.org/wiki/SATA

https://blog.codinghorror.com/understanding-user-and-kernel-mode/

https://en.wikipedia.org/wiki/Protection_ring