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Digital Literacy for Tech & STEM Work · How Computers Work

Hardware, software, and the OS

Reading29mLesson 1 of 3 in this module

Name the main parts of a computer and learn what the operating system does for every program you run.

Why it matters

Every career on this platform runs on computers: a data analyst's laptop, a lab's instrument PC, a PLC in a factory, a cloud server. When something is slow, crashes, or will not install, the people who fix it fastest are the ones who can picture what is going on inside the machine. You do not need to build a computer, but you do need a clear mental model of its parts.

The core idea: input, processing, storage, output

A computer takes input (keys, clicks, sensor readings, network data), processes it, stores results, and produces output (a screen, a file, a signal to a motor). The physical parts that do this are the hardware. The instructions that tell the hardware what to do are the software.

The main hardware parts

  • CPU (processor): runs instructions, one tiny step at a time, billions of times per second. Modern CPUs have several cores, so they can work on several tasks at once.
  • RAM (memory): fast, temporary workspace. Programs and the files you have open live here while you use them. RAM is wiped when the power goes off.
  • Storage (SSD or hard drive): slower, permanent space for files and installed programs. It keeps data when the power is off.
  • GPU (graphics processor): draws the screen and is also used for heavy parallel maths, such as 3D rendering and machine learning.
  • Motherboard: the circuit board that connects everything.
  • Input/output devices: keyboard, mouse, screen, USB ports, camera, and the network adapter (Wi-Fi or Ethernet).

A useful analogy: storage is your filing cabinet, RAM is your desk, and the CPU is you doing the work. A bigger desk (more RAM) lets you keep more things open without walking back to the cabinet.

Software comes in layers

  1. Firmware is built into the hardware and starts the machine (for example UEFI on a PC).
  2. The operating system (OS), such as Windows, macOS, Linux, Android, or iOS, loads next and manages everything.
  3. Applications (a browser, a spreadsheet, a code editor) run on top of the OS.

What the OS actually does

Applications almost never talk to the hardware directly. They ask the OS, and the OS handles:

  • Processes: it decides which program gets the CPU and for how long, switching so fast that many programs seem to run at once.
  • Memory: it gives each program its own area of RAM and stops programs from reading each other's memory.
  • Files: it organises storage into files and folders through a file system.
  • Devices: it uses drivers (small pieces of software) to talk to printers, cameras, graphics cards, and instruments.
  • Users and permissions: it controls who can sign in and which files or settings each person may change.

Worked example: opening a spreadsheet

You double-click results.xlsx.

  1. The OS sees the .xlsx extension and looks up which application is registered to open it.
  2. It loads that program from storage into RAM and creates a new process for it.
  3. The program asks the OS to read results.xlsx. The OS finds the file on the SSD through the file system and copies it into the program's memory.
  4. The CPU runs the program's instructions to work out what to draw, and the GPU puts it on the screen.
  5. When you press save, the program asks the OS to write the changes back to storage.

If your laptop slows to a crawl with 40 browser tabs open, you can now explain why: RAM is full, so the OS starts moving data back and forth to the much slower storage.

Check your own machine

Find out what you are working with:

  • Windows: Settings > System > About shows the processor and installed RAM.
  • macOS: Apple menu > About This Mac.
  • Linux: in a terminal, run:
lscpu | head -n 15   # processor details
free -h              # memory in use and available
df -h                # storage space per drive

Sizes use bytes: 1 KB is about a thousand bytes, 1 MB about a million, 1 GB about a billion, 1 TB about a trillion. A typical laptop has 8-32 GB of RAM and 256 GB-2 TB of storage.

Common mistakes

  • Confusing memory and storage. "My laptop has 512 GB of memory" usually means storage. Memory (RAM) is the smaller, faster number.
  • Thinking the OS is just the desktop. The wallpaper and icons are only the visible part. Most of the OS works in the background.
  • Ignoring updates. OS updates fix security holes and driver bugs. Installing them promptly is one of the cheapest ways to stay safe.
  • Blaming hardware first. Most "slow computer" problems are software: too many programs at start-up, a full disk, or a runaway process. Task Manager (Windows), Activity Monitor (macOS) or top (Linux) shows what is using the CPU and RAM.

Quick recap

  • Hardware is the physical machine: CPU, RAM, storage, GPU, motherboard, and devices.
  • Software runs in layers: firmware, then the OS, then applications.
  • The OS shares out the CPU and memory, manages files, drives devices, and enforces permissions.
  • RAM is fast and temporary; storage is slower and permanent.

Try it

Open the Do tab and take the quiz to check that you can name each part and what the OS does.

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