Difficulty: Beginner | Prerequisites: None
This is the opening material for an introductory computer science course. It covers what a computer actually is at a foundational level, the distinction between hardware and software, and the major physical components that make up a computer system. You need this vocabulary and these mental models before anything else in the course makes sense. If you are joining late, start here. Everything from programming to networking builds on these basics.
A computer is a machine that processes information under the control of stored programs. It is made up of hardware (the physical parts) and software (the instructions that tell the hardware what to do). The main hardware components are input devices, output devices, primary memory (RAM), secondary storage, and the CPU.
Computer
A machine that performs calculations and processes information, operating under the control of a computer program. Think of it as a general-purpose information processor that does exactly what its instructions tell it to do.
Computer program
A set of instructions that tells the computer what operations to perform. In simple terms, this is the recipe the computer follows.
Information processor
A way of describing what a computer fundamentally is: a device that takes in data, manipulates it according to instructions, and produces output.
Program control
The principle that a computer's actions are dictated by the software currently running. In simple terms, the computer does nothing on its own; it only does what a program tells it to.
Hardware
The electronic and mechanical components of a computer: the physical parts you can touch. This includes the CPU, memory chips, input/output devices, storage devices, and circuitry.
Software
The programs and instructions that control and coordinate hardware. Think of it as the invisible layer that makes the physical machine useful.
Application software
Programs designed for end users to perform specific tasks, such as word processors, spreadsheets, web browsers, and games.
System software
Programs that manage the hardware and provide a platform for running application software. The operating system is the most important example.
General-purpose computer
A computer that can store many different programs and perform a wide variety of tasks. Your laptop or desktop is a general-purpose computer.
Special-purpose computer
A computer designed for one specific task, with a fixed control program that cannot be changed. The microcontroller inside a microwave oven is a good example.
Input devices
Hardware that brings data into the computer, such as keyboards, mice, microphones, and scanners.
Output devices
Hardware that presents processed data in a human-readable form, such as monitors, printers, and speakers.
Human-computer interaction (HCI)
The exchange of data and information between a user and a computer, facilitated by input and output devices.
A computer performs calculations and processes information under the control of a stored program.
The core idea is program control: the machine does nothing without software directing it.
Computers handle everything from basic arithmetic to complex data analysis by executing instructions stored in memory.
Hardware is the physical infrastructure: CPU, memory, storage, circuitry, input/output devices.
Software is the set of instructions that tells the hardware what to do.
Neither is useful without the other. Hardware without software is an expensive paperweight. Software without hardware has nowhere to run.
Software splits into two broad categories:
Application software (word processors, browsers, games) serves the end user directly.
System software (the operating system, utilities) manages the hardware and provides a platform for applications.
General-purpose computers can store and run many different programs, making them flexible. Your laptop, phone, and tablet all fall here.
Special-purpose computers have fixed control programs built for one job. Examples include the chip in a microwave, a digital watch, or a basic calculator.
The trade-off: special-purpose machines are often more efficient at their one task, but they cannot do anything else.
Input devices bring data in (keyboard, mouse, microphone, scanner).
Output devices present results to the user (monitor, printer, speakers).
Primary memory (RAM) holds data and programs temporarily while the computer is on.
Secondary storage holds data permanently or long-term (hard drives, USB flash drives, optical discs).
Central Processing Unit (CPU) executes instructions and coordinates everything.
These five subsystems work together through a continuous flow of information.
Input devices convert human actions into signals the computer can process. A keyboard translates keystrokes; a microphone translates sound waves.
Output devices convert processed data back into a form humans can use. A monitor displays pixels; speakers produce audio.
Together, they form the bridge for human-computer interaction.
Every device you interact with daily, from your phone to a self-checkout machine, is built from these same fundamental components: input, output, processing, memory, and storage. Understanding this model is how engineers reason about any computing system, whether it is a smartwatch or a server rack.
Students often think "hardware" means just the computer case or the screen. It includes every physical component, down to the circuitry on the motherboard.
Students sometimes assume software is only the apps they download. The operating system is also software, and it is running before any app launches.
A special-purpose computer is still a computer. Students sometimes think the chip in a microwave "isn't really a computer," but it is: it processes instructions, just fixed ones.
"Memory" and "storage" are not interchangeable. RAM is temporary (volatile) memory. A hard drive is long-term (non-volatile) storage. Exams test this distinction.
⚠️ The distinction between hardware and software is foundational and appears in nearly every intro CS exam.
⚠️ Know the difference between general-purpose and special-purpose computers, with examples of each.
⚠️ Be able to list and describe the five main subsystems of a computer (input, output, RAM, secondary storage, CPU).
⚠️ Understand that a computer operates under program control, not on its own initiative.
True or false: A computer can operate without software. (False)
Fill in the blank: The principle that a computer's behaviour is dictated by its running program is called _______ _______. (Program control)
True or false: A calculator is an example of a general-purpose computer. (False, it is special-purpose)
Fill in the blank: Hardware that presents processed data to the user is called an _______ device. (Output)
True or false: Application software manages hardware resources. (False, that is system software)
Q: What is the fundamental definition of a computer?
A: A machine that performs calculations and processes information, operating under the control of a stored program.
Q: Name two differences between hardware and software.
A: Hardware refers to the physical, tangible components of a computer (CPU, memory chips, circuitry). Software refers to the programs and instructions that direct the hardware. Hardware provides the platform; software provides the purpose.
Q: Give two examples of special-purpose computers and explain why they are not general-purpose.
A: A microwave oven's microcontroller and a digital watch. They are special-purpose because they contain fixed control programs designed for a single task, and those programs cannot be changed or replaced with different software.
Q: What are the five main subsystems of a typical computer system?
A: Input devices, output devices, primary memory (RAM), secondary storage devices, and the central processing unit (CPU).
Q: Explain the difference between application software and system software, with one example of each.
A: Application software performs specific tasks for the user (e.g. a web browser). System software manages the hardware and provides a platform for applications to run (e.g. the operating system).
This material connects directly to the next set of topics on CPU architecture, memory hierarchies, and operating systems. The hardware/software distinction also sets the stage for understanding programming: when you write code, you are creating software that will control hardware through program control.
computer definition, hardware vs software, input devices, output devices, general-purpose computer, special-purpose computer, application software, system software, computer components, computer subsystems, information processor, program control, HCI, human-computer interaction, intro to computer science, CSCE 110