Operating Systems: Chapter 1 Definitions

• Important key definitions from Chapter 1 for a midterm exam

General Concepts

• Operating System (OS): Manages computer hardware, provides a basis for applications, and acts as an intermediary between the user and hardware.
• Kernel: The core of the OS; the one program running at all times.
• System Programs: Programs associated with the OS but not necessarily part of the kernel.
• Application Programs: Programs not associated with the operation of the system.
• Middleware: Software frameworks providing additional services to application developers, mainly in mobile OSes.
• Resource Allocator: Manages and allocates resources.
• Control Program: Controls the execution of user programs.

What Operating Systems Do

• Hardware: The physical components of a computer system like the CPU, memory, and I/O devices.
• User: Anyone who uses the computer.

Computer-System Organization

• CPU (Central Processing Unit): Executes instructions.
• Memory: Storage where the CPU can directly access instructions and data, typically RAM.
• I/O (Input/Output) Devices: Devices that allow computer interaction with the outside world (e.g., keyboard, mouse, monitor, disk drive).
• System Bus: A communication pathway connecting the CPU, memory, and I/O devices.
• Device Controller: Hardware that manages a specific type of device.
• Device Driver: Software providing a uniform interface to the OS for a specific device controller.
• Interrupt: A signal to the CPU that an event requires attention.
• Interrupt Service Routine (ISR): A routine that handles a specific type of interrupt.
• Interrupt Vector: A table of addresses pointing to the ISRs for different interrupt types.
• Interrupt-Request Line: A wire that the CPU senses to detect interrupts.
• Trap (or Exception): A software-generated interrupt, caused by an error or a system call.
• Nonmaskable Interrupt: High priority interrupt
• Maskable Interrupt: Low priority interrupt
• Bootstrap Program: The first program that runs when a computer powers on; it loads the OS.
• RAM (Random-Access Memory): Volatile main memory.
• Firmware: Storage that is infrequently written to and is nonvolatile (e.g., EEPROM).
• Volatile Storage: Loses its contents when power is lost.
• Nonvolatile Storage: Retains its contents when power is lost.
• Secondary Storage: Nonvolatile storage used for long-term data and program storage (e.g., HDDs, NVM devices).
• HDD (Hard-Disk Drive): A mechanical secondary storage device.
• NVM (Nonvolatile Memory) Device: An electrical secondary storage device (e.g., SSD, flash memory).
• DMA (Direct Memory Access): A method for transferring data between I/O devices and memory without CPU intervention.
• Bit: Smallest storage unit, either a one or a zero.
• Byte: A set of 8 bits.
• Word: One or more bytes, dependent on architecture.
• Kilobyte: 1024 bytes
• Megabyte: 1024^2 bytes
• Gigabyte: 1024^3 bytes
• Terabyte: 1024^4 bytes
• Petabyte: 1024^5 bytes

Computer-System Architecture

• Processor: A physical chip containing one or more CPUs.
• Core: The basic computation unit of the CPU.
• Multicore System: A system with multiple processing cores on a single CPU chip.
• Multiprocessor System: A system with multiple processors (which may be single-core or multicore).
• SMP (Symmetric Multiprocessing): A multiprocessor system where all CPUs are peers and can perform any task.
• NUMA (Non-Uniform Memory Access): A multiprocessor system where each CPU (or group) has its own local memory, but all CPUs can access all memory.
• Clustered System: Multiple independent computer systems working together, often for high availability.
• High Availability: The ability of a system to continue providing service even if some components fail.
• Parallelization: Breaking down an application into smaller pieces to be run at the same time

Operating-System Operations

• System Daemons: Background processes that provide system services.
• Multiprogramming: Keeping multiple processes in memory at the same time to increase CPU utilization.
• Multitasking (Time Sharing): Rapidly switching the CPU between processes to give the illusion of simultaneous execution and provide fast response times.
• Process: A program in execution.
• Virtual Memory: A technique that allows the execution of processes that are not completely in memory.
• User Mode: A CPU mode in which only non-privileged instructions can be executed.
• Kernel Mode (Supervisor Mode, System Mode, Privileged Mode): A CPU mode in which all instructions, including privileged ones, can be executed.
• Mode Bit: A hardware bit that indicates the current CPU mode (user or kernel).
• Privileged Instruction: An instruction that can only be executed in kernel mode.
• System Call: A request from a user program for the OS to perform a service.
• Timer: A hardware mechanism that can generate an interrupt after a specified period.
• Protection Rings: Levels of protection for system resources.

Resource Management

• File: A logical storage unit, representing a collection of related information.
• Cache: A set of faster storage locations

Security and Protection

• Protection: Any mechanism that controls access
• Security: Defending against attacks
• User Identifier: Unique per user, how the user is referenced in the system.
• Group Identifier: Allows a set of users to have specific permissions

Virtualization

• Virtualization: Abstracting hardware to provide different execution environments
• Emulation: Running a set of hardware using software