Computer Running Slow
Diagnose and fix a slow computer by finding what's hogging CPU, memory, and disk
A slow computer is almost always caused by something specific – not just "getting old." The usual suspects are a runaway process eating CPU, too many apps launching at startup, low disk space, or not enough RAM. Here's how to find and fix the problem on your OS.
- Open Activity Monitor – press Cmd + Space, type
Activity Monitor, and hit Return - Click the CPU tab and sort by % CPU (click the column header) to see what's using the most processor time
- If something you don't recognize is pinned near the top at 80%+ CPU, select it and click the X button in the toolbar to quit it
- Click the Memory tab and check the Memory Pressure graph at the bottom – if it's yellow or red, you're running low on RAM
- Sort by Memory to find the biggest consumers – web browsers with many tabs are usually the culprit
- Check your startup apps: go to Apple menu > System Settings > General > Login Items & Extensions and remove anything you don't need launching at boot (see the startup apps guide for details)
- Check free disk space: go to Apple menu > System Settings > General > Storage – if you're under 10-15 GB free, your Mac will slow down noticeably (see the disk cleanup guide for what to delete)
- Check for system updates: Apple menu > System Settings > General > Software Update – updates often include performance fixes
If Activity Monitor shows nothing unusual but your Mac still feels slow, check whether the issue is just in your browser (see browser running slow). If your Mac is physically hot and the fans are loud, it may be thermal throttling – see the overheating guide.
Frequently Asked Questions
How do I know if I need more RAM?▾
On Mac, check the Memory Pressure graph in Activity Monitor – if it's consistently yellow or red, you need more RAM. On Windows, open Task Manager and look at the Performance tab; if memory is consistently above 85-90%, more RAM would help. On Linux, check htop – if swap is heavily used, you're memory-constrained. 8 GB is the bare minimum for modern use; 16 GB is comfortable for most people.
Will restarting actually help?▾
Yes, genuinely. Restarting clears out memory leaks, finishes pending updates, and kills stuck processes. If your computer has been on for days or weeks, a restart alone may fix the slowness. Make it the first thing you try before digging deeper.
Is my computer just too old?▾
Maybe, but probably not. Computers from the last 5-7 years should still handle everyday tasks fine. The most impactful upgrade is adding an SSD if you still have a spinning hard drive – it makes everything dramatically faster. Adding more RAM is the second-best upgrade. A "slow old computer" with an SSD and 16 GB of RAM often feels brand new.
Why is my computer slow only when browsing the internet?▾
That's a browser problem, not a computer problem. See the browser running slow guide – the usual causes are too many open tabs, heavy extensions, or a bloated browser cache.
Why does my computer slow down after being on for a while?▾
Memory leaks. Some apps gradually consume more RAM the longer they run without being restarted. Browsers are the worst offenders. Restarting the app (or your whole computer) reclaims that memory. If it happens constantly, check Activity Monitor or Task Manager to identify which app is the leak.