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Operating Systems Basics

The software that manages everything else.

10 parts

Scroll to begin ↓

Applications ask the OS; the OS handles the hardware.

🧩 The partsWhat the OS actually doesPart 2 of 10

🔍 In detailFiles, folders and pathsPart 3 of 10

✏️ Worked exampleWhy a computer slows downPart 4 of 10

🔍 In detailTypes of operating systemPart 5 of 10

✏️ Worked exampleKeeping a system healthyPart 6 of 10

🌍 In the real worldWhy this is worth knowingPart 7 of 10

⚠️ Common mistakesWhere it usually goes wrongPart 8 of 10

✅ SummaryWhat to rememberPart 9 of 10

✏️ Worked exampleWatch one worked throughPart 10 of 10

1📘 DefinitionPart 1 / 10

The layer in the middle

An operating system manages the hardware and provides services that applications use.

Applications never touch hardware directly. A word processor does not know how your particular printer works. It asks the OS, which handles it.

Why that arrangement exists: without it, every program would need to support every possible printer, graphics card and disk. The OS provides one common interface, so software written once runs on thousands of different machines.

2🧩 The partsPart 2 / 10

What the OS actually does

Process management: decides which program uses the CPU and when. Your computer appears to run many programs at once by switching between them extremely fast.
Memory management: allocates RAM to each program and stops one from overwriting another's memory.
File management: organises data into files and folders on storage.
Device management: communicates with hardware through drivers.
Security: user accounts, passwords, permissions.
User interface: the desktop, or a command line.

3🔍 In detailPart 3 / 10

Files, folders and paths

Files are organised in a hierarchy: folders inside folders, forming a tree.

C:\Users\Ayesha\Documents\science\report.docx

That is a path, the full route to the file.

The extension after the dot tells the OS which program opens it: .docx .pdf .jpg .mp3 .exe.

A security point worth knowing: extensions can be misleading. A file named photo.jpg.exe is a program, not an image, and many systems hide the final extension by default, which is exactly what attackers rely on.

4✏️ Worked examplePart 4 / 10

Why a computer slows down

Understanding OS memory management explains the most common complaint about computers.

1. The CPU can only work with data in RAM.

2. When RAM fills, the OS moves less-used data to the much slower disk, called swapping or paging.

3. When that data is needed again, it must be read back from disk.

4. If this happens constantly, the computer spends its time shuffling data instead of working. Everything crawls.

What follows practically:

Closing unused programs and browser tabs frees RAM immediately.
Adding RAM often transforms an old machine; adding storage does nothing for speed.
An SSD helps because swapping becomes far less painful.

5🔍 In detailPart 5 / 10

Types of operating system

Windows: the most widely used on desktops; broad hardware and software support.
macOS: Apple hardware only; tightly integrated.
Linux: free and open source. Dominant on servers and the basis of Android.
Android / iOS: designed for touch, battery life and app sandboxing.

Open source means the code is public, so anyone can inspect, modify and share it. That has two consequences: security flaws can be found by anyone, and the software is free.

Why Linux dominates servers, no licence cost per machine, and it can be stripped down to exactly what is needed.

6✏️ Worked examplePart 6 / 10

Keeping a system healthy

Most computer problems are preventable with a few habits.

Update the OS. Updates are mostly security fixes for flaws that are already publicly known, which means postponing them leaves a known door open.

Back up, following the 3-2-1 rule: three copies, on two different types of media, one of them stored elsewhere. A backup on the same disk protects against deletion, not against the disk failing.

Do not install software you did not seek out. Most malware arrives with the user's permission.

Use a standard account, not an administrator account, for daily work. Malware runs with your permissions, fewer permissions means less damage.

Leave free disk space. A nearly full disk slows everything, because the OS needs room for swapping and temporary files.

7🌍 In the real worldPart 7 / 10

Why this is worth knowing

Diagnosing rather than guessing. Knowing what the OS manages lets you reason about whether a problem is RAM, disk, CPU or network.

Choosing hardware. Understanding the RAM/storage distinction prevents buying the wrong upgrade.

Security. Understanding permissions and file extensions defends against the most common attacks.

Careers. System administration is a substantial field, and it begins with exactly these ideas.

And a broader point: the OS is a good example of abstraction, hiding complexity behind a simple interface. That idea appears everywhere in computing.

8⚠️ Common mistakesPart 8 / 10

Where it usually goes wrong

"The OS is just the desktop." The interface is a small part.
"More storage makes it faster." RAM and CPU do.
"Apps talk to hardware directly."
"Updates are unnecessary." They are mostly security fixes.
"A backup on the same disk is a backup."
"Free software is low quality." Linux runs most servers.

9✅ SummaryPart 9 / 10

What to remember

The OS sits between applications and hardware.
It manages processes, memory, files, devices, security.
Slowness usually means RAM exhausted and swapping.
Update, back up 3-2-1, and avoid admin accounts for daily use.

10✏️ Worked examplePart 10 / 10

Watch one worked through

Here is one done slowly, with the reason for every move. Then one for you.

Watch one first

You have a browser, a music player and a word processor open at once on a computer with one processor. Explain how all three appear to run together.

Note the problem: one processor can only execute one instruction at a time.
1 CPU core = 1 task at any instant
Start from the limitation. The whole answer is about how the operating system works around it.
The operating system switches between them very fast.
browser → music → word → browser → ... milliseconds each
This is scheduling. Each program gets a slice of time in turn, which is why it is called time slicing.
The switching is faster than you can notice.
switch rate >> human perception → looks simultaneous
The programs are not really running at the same time. They take turns so quickly that it looks that way.
Name the other jobs the OS is doing meanwhile.
OS also: memory, files, devices
Scheduling is one of several jobs. The OS also stops one program reading another one's memory.

Answer: The operating system schedules them, giving each a tiny slice of processor time in turn, too fast to notice

Now you try

What is the name for the OS giving each program a small slice of CPU time? Two words.

Show the answer

time slicing

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Class 8 Computer Science: Operating Systems Basics

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