AP CSP Big Idea 4 (Computer Systems): How Computers Are Built and Managed

Computer system

A coordinated set of hardware and software that accepts input, processes it, stores data, and produces output.

Hardware

The physical components you can touch (chips, wires, keyboard, screen, storage devices, sensors, etc.).

Software

Programs/instructions that tell hardware what to do; can exist in layers (OS, drivers, firmware, apps).

General-purpose machine

A computer that can perform many different tasks because software can reconfigure how the same hardware behaves.

CPU (Central Processing Unit)

The main processor that executes program instructions step-by-step.

Fetch–decode–execute cycle

The repeated CPU process of fetching an instruction from memory, decoding it, executing it, and repeating rapidly.

ALU (Arithmetic Logic Unit)

The CPU subcomponent that performs arithmetic operations and logical comparisons.

RAM (Random Access Memory)

Fast, short-term working memory that holds the data and instructions the CPU needs right now; typically volatile (clears when power is off).

Storage (persistent storage)

Long-term data storage (e.g., SSD, HDD, flash) that keeps files and programs even when power is off.

Input device

Hardware that sends data into the computer (keyboard, mouse, touchscreen, microphone, camera, sensors, scanner).

Output device

Hardware that presents results from the computer (display, speakers, printer, vibration motor).

Network interface hardware

Hardware that connects a device to networks (NIC, Wi‑Fi chip, cellular modem) by sending/receiving bits over a medium.

System software

Software that runs and manages the computer and provides a platform for apps (especially the operating system; also utilities/tools).

Application software

Software used by people to perform tasks (browser, game, photo editor, spreadsheet).

Operating system (OS)

Foundational system software that manages hardware resources and provides common services for applications (CPU, memory, files, devices, security).

Kernel

The core part of an operating system responsible for controlling and allocating hardware resources.

Process

A program that is currently running, including its current state and allocated resources.

Thread

A smaller unit of execution within a process; multiple threads can run within one process.

CPU scheduling

The OS task of deciding which process/thread gets CPU time at a given moment (enables multitasking via rapid switching).

Memory management

The OS function that tracks and allocates RAM, enforces memory protection, and handles situations when memory is scarce.

File system

The OS method for organizing and managing files on storage using abstractions like files, folders/directories, paths, and permissions.

Firmware

Low-level software stored on hardware (often non-volatile) that helps control hardware and initialize devices during startup.

Device driver

Software that lets the OS communicate with a specific hardware device by translating OS requests into device-specific commands.

API (Application Programming Interface)

A set of functions/rules that software uses to interact with other software (often provided by the OS or libraries).

System call

A mechanism by which an application requests a service from the OS (e.g., read a file, use the network) instead of controlling hardware directly.