Why is my computer so slow?

A slow computer is the most common complaint there is, and the usual advice is either to buy a new one or to install a “cleaner” program. Both are frequently wrong.

Here is what actually causes it, roughly in order of how often I find each one.

1. It has a spinning hard drive

This is the biggest single cause of slowness in older machines, and the easiest to fix.

Computers made before about 2016, and cheap ones made since, often use a mechanical hard drive: a physical spinning disk with a moving arm, essentially a record player. Modern machines use an SSD, which has no moving parts.

The difference is not incremental. Replacing a mechanical drive with an SSD typically takes a machine that needs three minutes to start up down to about fifteen seconds. Everything feels immediate again.

An SSD costs well under a hundred dollars for a size most people will never fill. Fitting one, moving your files across and reinstalling Windows is a couple of hours of work.

If your computer is slow, is over five years old, and has a mechanical drive, this one change will do more than everything else on this list combined. It is the difference between a frustrating machine and a perfectly pleasant one.

You can check which you have: press Ctrl, Shift and Escape together to open Task Manager, click Performance, and look at the Disk entry. It will say either HDD (mechanical) or SSD.

2. Too many programs starting with the computer

Software installs itself into the startup list constantly, usually without asking clearly. Years of that accumulates.

Windows: Ctrl, Shift and Escape, then the Startup tab. You will probably see a long list. Right click and disable anything that does not need to run from the moment the computer turns on. Almost nothing genuinely does.

Do not disable anything from your antivirus, or anything with “audio”, “graphics” or “touchpad” in the name. Everything else is fair game and can be re-enabled if you miss it.

Mac: System Settings, General, Login Items.

3. Not enough memory

Memory, or RAM, is the working space the computer uses while running things. Run out and it starts shuffling data to the much slower drive, which is exactly when everything crawls.

4GB is not enough for a modern computer with a browser open. 8GB is a workable minimum. 16GB is comfortable.

Check in Task Manager under Performance, Memory. If it sits above 80% during normal use, more memory would help. It is often an inexpensive upgrade on a desktop and sometimes possible on a laptop.

4. Far too many browser tabs

An unfashionable answer, but a common one. Each open tab consumes memory, and people routinely run forty or more without noticing.

If the computer is only slow while browsing, this is very likely the cause. Close what you are not using, and bookmark instead of leaving tabs open.

5. Extensions and toolbars

Browser add-ons accumulate, and many arrive bundled with other software. Some are outright malicious, and a great many simply slow everything down.

In your browser’s settings, find Extensions and remove anything you did not deliberately install and do not actively use.

6. It is genuinely full

A drive with almost no free space slows down noticeably, because Windows needs working room. Aim to keep at least 10% free, and preferably 20%.

Windows: Settings, System, Storage, and turn on Storage Sense. Then look at what is using the space. Usually it is videos, downloads and old restore points.

7. Something unwanted is running

Malware, unwanted advertising software and bundled “optimisers” all consume resources.

Windows Defender is built into Windows, is genuinely good, and needs no help. Run a full scan from Windows Security. Malwarebytes is worth a free scan too.

Then remove any program you did not intend to install, from Settings, Apps.

What does not help

“PC cleaner” and “speed booster” programs. These are, almost without exception, a waste of money at best. Many are the problem rather than the solution: they nag, they run constantly, and some quietly install advertising. Windows already includes everything genuinely useful that they claim to do.

Deleting temporary files daily. It reclaims a little space and does essentially nothing for speed.

Defragmenting. This mattered on mechanical drives twenty years ago. Windows handles it automatically now, and on an SSD it should not be done at all.

Registry cleaners. No measurable benefit, and a real risk of breaking things.

When it genuinely is time for a new one

Sometimes it is. Consider replacing rather than repairing if:

• It cannot run a supported version of Windows and no longer receives security updates
• Adding memory and an SSD would cost more than half the price of a new machine
• It is more than about eight years old and you use it heavily
• The screen, keyboard or battery have failed as well

Before you buy anything, though, it is worth having someone look at it honestly. I regularly see machines that people had written off entirely, where an SSD and an hour of tidying produced something they were happy with for another three years.

That is not a sales pitch. It is the opposite: ask before you spend money, because the answer is often that you do not need to.