Computer basics

What is an operating system

An operating system is the software that stands between the hardware and every other program: it decides which program gets the processor and when, where files are written, and who is allowed to touch what. Without it every program would have to talk to every component directly, and no two programs could share one machine.

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Four families, and the work each one actually sits in

The columns are the families and the cards are where they actually get used. Note that the last column is itself two operating systems, and one of them is Linux underneath.

  1. Windows

    2
    • Office and home computers

      On hardware from thousands of makers

    • Industrial and accounting software

      The thing that takes the choice out of your hands

  2. macOS

    2
    • Creative work: video, graphics, audio

      Only on Apple own hardware

    • Building iOS apps

      A registered UNIX, so its command line is a relative of servers

  3. Linux

    2
    • Servers and web infrastructure

      Including the one that handed you this page

    • Keeping an old laptop alive

      Test it with your own real files first

  4. Mobile

    2
    • Android

      Its kernel is based on a long term supported Linux kernel

    • iOS

      Apps from one store, each in its own box

This chart says where each is common, not which is better. There are no market share numbers here, because we had no primary source for any.

Last checked: Facts and tool names in this lesson are re-checked against their sources on this date.

What does an operating system actually do

An operating system does four things, and all four resemble the work of a building manager: sharing out something scarce among people who each want all of it.

It shares processor time. At any instant a processor does as many things as it has cores, and the number of things wanting to run is far larger. The operating system gives each one a few thousandths of a second and moves on to the next, fast enough that they all appear to run together. None of the programs knows it is being set aside over and over.

It shares memory and holds the borders. Every program believes the memory is its own. The operating system builds that illusion and at the same time stops any program from reaching into another one memory. When one program crashes and the rest survive, that border is what worked.

It organises files. A disk is really a long row of numbered blocks, and there is no such thing as a folder on it. Folders, files and paths are made by the operating system so that you never have to work with block numbers.

It enforces permissions. This is the least visible part and the one with the widest effect. Every file has an owner, and it is written down who may read it, change it or run it. A program without permission does not negotiate; the answer is no, and that is the end of it.

There is a fifth job that stays out of sight: the operating system talks to components through drivers, the code the maker of each component wrote. That is why an old printer stops working on a new Windows: the printer is fine, its driver was never written for this version.

A glass layer between a red hardware block and green and blue app blocks with a white controller light

You are standing on the outermost layer

No program talks to the components directly. Every request is passed from the outside inwards, and the answer comes back the same way.

Hardware
  1. 1

    Kernel and drivers

    The only part that genuinely touches the components

  2. 2

    Operating system services

    Files, networking, permissions, scheduling

  3. 3

    Programs

    Browser, office, games; none is allowed into the inner layer

  4. 4

    You

    Clicks and typing; everything moves inward from here

The border between the two middle layers is not in exactly the same place on every system; this model is for grasping the order, not a technical map of any one operating system.

How Windows, macOS, Linux and mobile differ

All four families do the same four jobs from the previous part. The difference is elsewhere: who each one was built for, and what hardware it is allowed to run on.

Windows installs on hardware from thousands of different makers, and the largest body of office, industrial and gaming software was written for it. That same breadth is its biggest weakness: it has to cope with every odd combination of parts anyone assembles.

macOS runs only on Apple own hardware, and that restriction is what produces its consistency. One thing that gets said less often: macOS is a formally registered UNIX, not something UNIX like; The Open Group register currently carries two separate registrations for macOS version 26 on Apple silicon and on Intel Macs. The practical consequence for you is that its command line is a relative of Linux and of servers.

Linux turns up everywhere except where people go looking for it. Most of the web servers in the world, including the one handing you this page, run it. On the desktop it is entirely usable, but the next part says where the cost sits.

Android and iOS are the mobile operating systems, and they differ from the other three in two ways: programs come from one central store, and each program runs in a separate box with no direct access to the rest of the device. Android is Linux underneath as well; Google own documentation states that the Android kernel is based on an upstream Linux Long Term Supported kernel. So your phone, contrary to how it looks, belongs to the same family as the servers.

We have deliberately printed no market share numbers. The figures traded around on this subject rarely come from a primary source, disagree with each other in strange ways, and do nothing at all for your decision.

Why an old operating system is dangerous

An old operating system does not turn slow or broken on day one. What changes is this: from a certain date, the security flaws that get found are no longer patched for it.

A precise, dated example: Microsoft ended support for Windows 10 on 14 October 2025. Their own page states that after that date, Windows 10 computers no longer receive technical support, software updates or security fixes. The machine still switches on, everything still works, and that is exactly what fools people.

The arithmetic is simple. Every security flaw found in that version from that day onward is, for an attacker, an open door that will never be closed. A current operating system has flaws too; the difference is that its flaws get shut. So the risk accumulates with time rather than staying level.

And here is the boundary of the claim, because without it this becomes scaremongering: a computer that never touches a network and only drives one old machine is fine on an old operating system. In workshops that situation genuinely exists. The danger belongs to the machine that has a browser, receives email and opens files from outside.

What switching operating systems really costs

The usual question is which one is better. The more useful question is what moving from this one to that one takes away from you.

There are three real costs and none of them is the price of the operating system. First, software that exists on only one of them. If your work is tied to an accounting package or an industrial application that is Windows only, the discussion is over and no other argument matters. Second, habit. The first week everything goes slower, and that is a real cost even when it never appears on paper. Third, attached hardware: printers, scanners, card readers, anything that needs a driver.

There is a cost in the other direction too, and it gets mentioned less. Moving an old laptop to Linux usually keeps that machine usable, but if your work involves office files that have to open exactly as they do for your client, the layout sometimes shifts, and that one item can wipe out the whole saving. You cannot learn this from marketing pages; you have to try it with your own real files.

There is a middle route that is often overlooked: run the new operating system from a USB stick, without installing it, and do one real working day on it. If something breaks that day, you have lost nothing yet.

Staying or switching, with the real cost of each side

The two pans are deliberately level. The right answer depends on your work, not on which operating system has more supporters.

Staying on this operating system

  • Every work program keeps running with no testing
  • Printer, scanner and the other peripherals stay as they are
  • But if the version is out of support, security fixes stop arriving

Moving to another operating system

  • Security updates come back
  • An old laptop usually stays usable for a few more years
  • But you work slower for a week and every peripheral has to be tested again

One cost sits in neither pan because it cannot be measured: the day you hit a problem mid job and nobody near you knows that system.

So which one should I pick

Our position: for most people this is not really a choice. The work you have to do, and the software that work needs, decide the answer, and the rest is taste.

Three clear cases: if one essential program exists on only one of them, take that one and do not argue about it. If your work is video, graphics or iOS app development, Apple hardware is a defensible choice, though not the only one. And if you have a laptop of a few years old that cannot breathe under a new Windows, Linux buys it the most extra life, provided you test it with your own real files first.

One point that carries over to running a website: the server your site sits on is almost always Linux, even when your own computer is Windows. If you work with Linux hosting, the file ownership and permission ideas from the first part of this lesson are exactly what you meet there.

The natural next step is to see how this same operating system keeps files and folders, and why a file extension is not the thing you think it is.

The fast path, with AI

The usual route for any operating system error message is to paste it into a search engine and land on the first forum. The faster route is to hand the error to a model, but not with the question "how do I fix this". The move that changes everything is to make the model take apart any command it proposes before you run it, and say plainly which step is irreversible.

  1. Copy the error text exactly, not from memory. An error number with one digit changed is a different problem.
  2. Give it the recipe below. The job here is translation and dissection, not judgement, so a fast cheap model is enough; see the AI section of this site for the current pick.
  3. Read the answer from the bottom. If the "irreversible" column is marked for a step, do not run that step until a second source confirms it.
  4. Before any change that touches files, take a backup. No model does this step for you.

Copy-ready recipe

Operating system: {e.g. Windows 11 version 24H2}
What I was doing: {exactly what}
The error message, verbatim: {full text}

1. What this message means in plain words.
2. Three likely causes, most likely first.
3. For each cause, one way to check it that changes nothing.
4. Then the fixes, as a table with these columns:
   step | what it changes | irreversible or not
5. For every command you write, break it apart and say what each piece does.
If you are not sure, write that you are not sure. Do not give a guess as an answer.

Before you trust the output: The fourth step is not a formality, and this lesson itself is the reason: permissions are enforced by the operating system and it does not negotiate. A command run with administrator rights does not ask twice, and a deletion made that way has no recycle bin. Never run a command you cannot explain yourself, word by word, however confidently it was written.

AI in this kind of work

On this subject AI has one real advantage, and it is translation: operating system error messages are written in engineer language and models turn them into human language well. The second thing they do well is finding the path to a setting, because those paths move with every version. Our position: use a model to understand, not to execute.

Tools that actually help

  • Gemini For translating an error message and finding the path to a setting in newer versions. Iran is not on Google own supported countries list; the detail is on this tool page on this site.
  • Claude Answers the "break this command apart before I run it" job well and is readier to say it does not know. Iran is on neither of the company two supported countries lists.
  • ChatGPT For common Windows error messages that have been repeated thousands of times online. Same access limitation, and its accuracy drops for very recent versions.

Where it backfires

The main risk here has a particular shape and differs from other subjects: a command the model writes is one you then run with full authority. And the operating system, as we said above, does not negotiate; an order given with administrator rights is carried out, full stop. Google own privacy page for Gemini says plainly that responses may be inaccurate, and in this subject "inaccurate" means a command that looked right and emptied the wrong folder. The second risk is the familiar screenshot one: a picture of your desktop carries file names, tab titles and notification text along with it, and that same Google page says not to enter information you would not want a human reviewer to see. Type the error text; do not send the picture of the screen.

Sources: Google: Gemini Apps Privacy Hub (last updated 10 August 2026) Anthropic: is my data used for model training

Where this advice stops

This lesson is about desktop and mobile operating systems for an ordinary user. It does not tell you which Linux distribution to take, because that answer depends on your patience and skill rather than on a rule. The "an old operating system is dangerous" rule has one real exception, stated in the text: a machine attached to no network at all. And the last boundary, which is the most important: very often the choice is not yours. A work laptop, or one required application that exists on one system only, ends the discussion before it starts.

From our own work

How an operating system shares processor time can be seen on this very server. The machine runs Ubuntu 24.04.4 with kernel 6.8.0-139 and has 4 cores. At the moment we looked, 238 processes and 576 threads of execution were open on it and the system load average was 0.39. That is 576 things entitled to run, 4 of them actually on the processor at any instant, and not one of the sites on this machine noticed. The second half of the lesson, permissions, is where we have paid the price ourselves: the web server runs as the user www with id 1000, and every file under the site root has to belong to that user. One file written as root is enough for the web server to be unable to write to it, and it happens silently. That is why the header of our own tool for this section, /root/seo-engine/bin/learnhub.sh, records that the WordPress command line tool is never run as root, because the cache directory ends up owned by root and the cache layer quietly stops writing. The operating system makes no exceptions.

Real follow-up questions

My Windows 10 still works; do I have to change it?

If that computer connects to the internet, receives email or opens files from outside, then yes, and the longer you wait the more it costs. If it is a machine that never touches a network and does one specific job, it can stay. Support ended on 14 October 2025, and no security fixes have come for that version since.

Is Linux hard for an ordinary user?

For browsing, email, video and ordinary office work, today no; installing it is no harder than installing Windows. The difficulty is elsewhere: one specific program that is Windows only, or a printer with no Linux driver. So the right question is not "is it hard" but "does my one essential program exist on it".

Does changing the operating system make a computer faster?

Sometimes noticeably, but not as much as it is advertised and not always. A lighter operating system on an old machine takes less memory for itself, and that is the difference it makes. But if the real problem is a mechanical drive or too little memory, changing the operating system only covers part of it, and the computer hardware lesson explains why.

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