What is a Computer System?

A computer is an electronic device that operates under the control of instructions (software) stored in its memory.

It performs three basic operations: it accepts data (Input), manipulates it (Process), and produces information (Output).

A computer system is a collection of hardware, software, and peripheral devices that function together to accomplish tasks.

The Information Processing Cycle

Computers process raw data into useful information. This follows a four-stage cycle:

• Input: Raw facts, figures, and symbols are entered into the computer.
• Process: The computer manipulates the data to create meaningful information.
• Output: The created information is presented to the user.
• Storage: The information is saved for future use.

Primary Components of a Computer

Every computer system is built around four primary functional units that work together.

• Input Units: Allow users to enter data (e.g., keyboard, mouse).
• Processing Unit (CPU): The "brain" that executes instructions.
• Storage Units: Hold data and programs (e.g., RAM, SSD).
• Output Units: Display results (e.g., monitor, printer).

The Central Processing Unit (CPU)

The CPU is the electronic circuitry that executes instructions, making it the core of a computer system. It's often called the "brain" of the computer.

Its primary jobs are to:

• Interpret and execute program instructions.
• Perform arithmetic and logical operations.
• Manage the flow of data throughout the system.

Inside the CPU

The CPU itself is composed of several key components, each with a specific role:

• Control Unit (CU): Directs the processor's operations, fetching and decoding instructions.
• Arithmetic Logic Unit (ALU): Performs all math (+, -, ×) and logical (AND, OR, NOT) operations.
• Registers: Tiny, extremely fast storage locations within the CPU for temporary data.
• Cache: A small, fast memory that stores frequently used data to speed up processing.

Storage Units

Storage units are the devices that hold data, instructions, and information for future use. They are broadly classified into two types.

Primary Storage:

• Directly accessible by the CPU.
• Volatile: data is lost when power is turned off (e.g., RAM).

Secondary Storage:

• Used for long-term, non-volatile storage.
• Slower than primary storage (e.g., SSD, Hard Drive).

A Closer Look at Primary Storage

Primary storage is crucial for active operations. There are three main types:

• RAM (Random Access Memory): Stores data and programs the CPU is actively using. It's fast but volatile.
• ROM (Read-Only Memory): Stores permanent instructions for booting the computer (firmware). It's non-volatile.
• Cache: The fastest and smallest type of memory, acting as a buffer between the CPU and RAM.

The Storage Hierarchy

Computer storage is organized in a hierarchy based on speed, cost, and capacity. As you move up the pyramid, storage gets faster and more expensive, but smaller in capacity.

This structure allows the system to balance performance and cost effectively. The CPU has the quickest access to the data it needs most often.

Hover over the levels in the diagram to learn more.

The Motherboard: The Central Hub

The motherboard is the main printed circuit board that connects all the components of a computer system.

It acts as the central backbone, allowing communication between the CPU, RAM, storage devices, and all peripherals.

Think of it as the nervous system of the computer, ensuring every part can talk to every other part.

Types of Computers by Scale

Computers come in various sizes and processing powers, designed for different tasks.

• Supercomputers: The most powerful, for complex scientific calculations.
• Mainframes: Large systems for bulk data processing (e.g., in banks).
• Minicomputers: Mid-sized servers for businesses.
• Microcomputers: Personal computers like desktops, laptops, and smartphones.

Computer Software Categories

Software is the set of instructions that tells the hardware what to do. It exists in layers, with each layer relying on the one below it.

• Application Software: Programs for user tasks (e.g., browsers, games). This is what you interact with directly.
• System Software: Manages the hardware and provides a platform for applications (e.g., Windows, macOS, drivers).

The Operating System (OS)

The Operating System is the most important piece of system software. It acts as the intermediary between the user and the computer hardware.

Without an OS, a computer is just a collection of electronics. The OS manages all the hardware and software resources, making the computer usable.

Popular examples include Windows, macOS, Linux, Android, and iOS.

Key Functions of an Operating System

The OS performs many critical tasks behind the scenes to keep the computer running smoothly.

• Process Management: Controls the execution of programs (multitasking).
• Memory Management: Allocates RAM to different processes.
• File System Management: Organizes files and folders on storage devices.
• Device Management: Allows software to communicate with hardware like printers and keyboards.

The Boot Process

Booting is the process of starting a computer. It's a sequence of operations that loads the operating system into memory so it can take control.

This step-by-step process ensures all hardware is working correctly before the user can interact with the system.

The animation on the right illustrates the key stages of a typical "cold boot" from a powered-off state.