Why is my computer so slow?

Slowness has a small number of causes and they are diagnosable. Guessing at fixes wastes an afternoon; spending ten minutes finding out which resource is exhausted tells you exactly what to do.

What you'll need

• Your computer
• External drive for backup (optional)

Step by step

1. Check free disk space first.Below about 10-15% free, both Windows and macOS slow down noticeably. This is the most common cause and the easiest to fix.
2. Open the task manager and look at what is using the machine.Windows: Ctrl+Shift+Esc. Mac: Activity Monitor. Sort by CPU, then by memory. One process at 100% explains a lot.
3. Check the startup list.Windows Task Manager's Startup tab, or Mac System Settings, General, Login Items. Programs launching at boot run all day whether you use them or not.
4. Check memory pressure.If memory is consistently full, the machine is swapping to disk, which is dramatically slower. Closing browser tabs is the fastest test of this.
5. Check for overheating.A hot machine with loud fans throttles its own speed to protect itself. Blocked vents and dust are the usual reason.
6. Check whether the drive is a hard disk rather than an SSD.A mechanical hard drive is the single biggest bottleneck in an older machine. An SSD upgrade transforms it more than any other change.
7. Restart properly, and do it regularly.Not sleep or shut lid — a full restart. Memory leaks and stuck processes accumulate over weeks of uptime.
8. Check for pending updates.A machine mid-update or with a large backlog runs background work constantly until it finishes.

Tips

• Browsers are usually the largest memory consumer on a modern machine. Thirty open tabs is a real workload, not an idle state.
• If the machine is slow only in a browser, the problem is extensions or tabs, not the computer.
• An SSD and more memory will rejuvenate a machine that is otherwise sound, and both are usually far cheaper than replacing it.

Common mistakes

• Installing an optimiser or cleaner tool — They rarely address the actual bottleneck, add their own background load, and some are outright malware.
• Assuming it needs replacing — Full disk, startup bloat and a mechanical hard drive are all fixable, often for very little money.
• Never restarting — Closing the lid is not a restart. Weeks of uptime accumulate leaked memory and stuck processes.

Questions people ask