How do I use Task Manager or Activity Monitor to find what is slowing my computer down?
The column that is pegged tells you the fix. Reading the four resources properly turns "my computer is slow" into a specific, solvable problem.
- Difficulty
- beginner
- Time
- 25 min
- Read
- 4 min
- Safety
- caution
Short answer
Open Task Manager on Windows or Activity Monitor on a Mac, sort by each of the four resources in turn, and see which one is at its limit while the machine is slow. Processor pegged means one program is doing too much work. Memory full means too much open at once, and the machine is now swapping to disk. Disk at its limit means the drive is the bottleneck. Network high means something is uploading or downloading. Each has a different answer.
Most people open the task manager, look at a wall of unfamiliar names, and close it again. The trick is not to read the names at all to begin with. Sort by each column, find the one thing at the top of the one column that is saturated, and only then worry about what it is called.
Safety
Step by step
- Open it while the machine is slow.The reading is only useful during the problem. On Windows, the keyboard shortcut that brings up the security screen offers Task Manager; on a Mac, Activity Monitor is in the Utilities folder and can be kept in the dock. If the slowness is intermittent, leave it open and watch.
- Sort by processor first.Click the CPU column to sort descending. Short spikes are normal. One process sitting at a high figure for minutes is your answer. Note that on Windows a figure near 100 per cent means the whole processor; on a Mac, Activity Monitor counts each core separately, so a single-threaded process can legitimately show several hundred per cent on a multi-core machine.
- Sort by memory.Look at the total in use against the total installed, and at the memory pressure graph on a Mac, which is more informative than the raw figure. Memory near capacity means the system is moving data out to the drive to make room, and that swap is what makes everything feel treacle-like.
- Sort by disk.On Windows the disk column shows a percentage of the drive's capability; on a Mac, look at the disk tab's read and write rates. A drive pinned at its limit while nothing obvious is happening usually means indexing, an update, a backup, antivirus, or a failing drive.
- Sort by network.A large sustained transfer explains both a slow machine and a slow connection. Cloud sync after a large change, an operating system update downloading, or a game updating in the background are the usual causes.
- Identify the culprit before ending it.Search the process name. Many alarming-looking names are legitimate parts of the operating system. If it is a program you recognise and it has hung, end it. If it is a system component, restart the machine instead of ending it.
- Look at what starts automatically.Task Manager has a startup tab and macOS has login items in its settings. A machine that is slow for ten minutes after every start has too much launching at login, and this is the single most effective thing to prune.
- Distinguish the pattern.Slow all the time points to hardware or a resident program. Slow at start points to login items. Slow occasionally in bursts points to scheduled work — backups, indexing, antivirus scans, updates. The pattern narrows it faster than any single reading.
If it doesn't work
One process at high processor usage constantly
Cause: A program stuck in a loop, a browser tab with heavy content, or an update process — Fix: Close and reopen the program. If it recurs, update it or remove it. Browser tabs are the most common cause on modern machines, and browsers have their own task manager that names the offending tab.
Memory nearly full with nothing obviously open
Cause: Browser tabs, background applications, and a memory leak in a long-running program — Fix: Restart the offending application. Restart the machine if you cannot identify it. If it happens daily with modest use, the machine may genuinely need more memory.
Disk pegged for long periods on a new or freshly updated machine
Cause: Search indexing or an update installing in the background — Fix: Leave it alone for an hour or two — indexing genuinely finishes. If it never finishes, look at the drive's health, because a failing drive produces the same reading.
High activity attributed to a process with an unfamiliar name
Cause: Usually a legitimate system service; occasionally unwanted software — Fix: Search the exact name plus the operating system. Check where the file lives — legitimate system processes live in system folders. Do not end it on suspicion alone.
Everything looks idle but the machine is still slow
Cause: Thermal throttling, a failing drive, or a low-power mode — Fix: Check whether it is hot and the fans are running, check the drive's health, and check the power mode and whether the charger is connected.
Questions people ask
Is high memory usage bad?
No. Unused memory is wasted memory, and both systems deliberately fill it with cached data they can discard instantly. What matters is whether the system is under pressure and swapping — the memory pressure graph on a Mac, and the swap or paging figures on Windows.
Should I end processes to speed things up?
Only ones you recognise and want closed. Ending things at random produces instability and does not free anything the system was not already prepared to release.
What does the disk figure of 100 per cent mean on Windows?
That the drive is being asked for as much as it can deliver, not that it is full. On an older mechanical drive this is easy to reach, which is why an SSD upgrade transforms exactly those machines.