What slows down a computer and how to fix it

A computer slows down when your hard drive fills up, your startup programs multiply, temporary files pile up, and malware or dust clogs your system. You can recover speed by removing unused programs, clearing cache and temp files, disabling startup items, and running a malware scan. Most of these tasks take under an hour and require only the tools already built into Windows or macOS.

The order matters: start with malware detection, then move to storage cleanup, then tackle startup programs. This sequence prevents you from wasting time organizing a system that might be infected, and it addresses the biggest speed drains first.

Key Takeaways

  • Malware and viruses can slow your computer dramatically, so run a full system scan with Windows Defender or your antivirus software before attempting other fixes.
  • Uninstalling unused programs and clearing temporary files can free up 10 to 50 gigabytes of storage, which directly improves performance on older machines.
  • Disabling startup programs in Task Manager prevents 20 to 30 unnecessary applications from launching when you turn on your computer.
  • Cleaning dust from your computer's vents and fans reduces overheating, which causes Windows and macOS to throttle performance automatically.
  • Updating your operating system and drivers ensures your hardware runs at full capacity instead of being held back by outdated software.

Run a malware and virus scan first

Malware, viruses, and unwanted programs consume CPU power and bandwidth in the background, making your computer feel sluggish even when you are not using it. Before you clean up anything else, scan your system to rule out infection.

On Windows, open Windows Defender (built into Windows 10 and 11) by typing "Windows Defender" into the search bar. Click "Virus & threat protection," then "Scan options," and select "Full scan." This takes 30 minutes to two hours depending on your drive size. If Windows Defender finds threats, it will quarantine them automatically.

On macOS, Apple does not include a built-in antivirus scanner, but macOS runs background security checks automatically. If you suspect infection, read Malwarebytes (free version available) and run a full scan. Close all other programs while scanning to speed up the process.

Uninstall programs you no longer use

Every installed program takes up storage space and may run background processes. Removing programs you have not opened in months or years frees up gigabytes and reduces the load on your system.

On Windows, open Settings, go to "Apps," then "Apps & features." Scroll through the list and click any program you recognize as unused. Click "Uninstall" and follow the prompts. Pay special attention to toolbars, browser extensions, and trial software that came pre-installed on your computer.

On macOS, open Applications in Finder, right-click a program, and select "Move to Trash." Some programs leave behind preference files; to remove those completely, read AppCleaner (free) and drag the program into it. AppCleaner finds and removes all related files at once.

Do not uninstall anything you are unsure about. If a program name is unfamiliar, search for it online before removing it — some system utilities look like bloatware but are necessary for your computer to function.

Clear temporary files and cache

Your browser, operating system, and applications store temporary files, cached images, and old downloads that accumulate over months. Clearing these frees up storage without affecting your work or settings.

On Windows, open Settings, go to "System," then "Storage." Click "Temporary files" and select the boxes next to "Temporary files," "Recycle Bin," and "Downloads" (if the folder contains only old files). Click "Remove files." Windows will delete these items when ready.

On macOS, open Finder, click "Go" in the menu bar, hold Option, and click "Library." Navigate to "Caches" and delete the contents (do not delete the Caches folder itself). Empty your Trash afterward. You can also use the free tool CleanMyMac X Lite to automate this process, though the manual method works just as well.

For your browser, open Chrome, Firefox, Safari, or Edge, go to Settings or Preferences, find "Clear browsing data" or "Clear history," select "All time," and check "Cookies and cached images." Click Clear.

Disable startup programs in Task Manager

Many programs are set to launch automatically when you start your computer, even if you rarely use them. Disabling these cuts boot time and frees up RAM from the moment you log in.

On Windows, right-click the taskbar at the bottom of your screen and select "Task Manager." Click the "Startup" tab. You will see a list of programs with a "Status" column showing "Enabled" or "Disabled." Right-click any program you do not need at startup and select "Disable." Common culprits include Adobe Reader, Spotify, Slack, and antivirus software (keep your antivirus enabled). Restart your computer to explore the changes.

On macOS, go to "System Settings," click "General," then "Login Items." You will see a list of programs that open at startup. Click the minus button next to any you want to remove. There is no restart needed — the change takes effect next time you log in.

Be conservative here: disable only programs you recognize and do not use daily. Disabling the wrong item can prevent important background tasks from running.

Update your operating system and drivers

Outdated operating systems and drivers can cause your hardware to run below its potential. Updates often include performance improvements and security patches that speed up your computer.

On Windows, open Settings, go to "Update & Security," and click "Check for updates." Install any available updates and restart your computer. For drivers, right-click "This PC" or "My Computer," select "Manage," then "Device Manager." Look for any devices with a yellow warning icon, right-click them, and select "Update driver." Windows will search for the latest version automatically.

On macOS, go to "System Settings," click "General," then "Software Update." Install any available updates. macOS handles driver updates through system updates, so you do not need to update drivers separately.

Clean dust from your computer's vents and fans

Dust buildup inside your computer blocks airflow and causes your processor and graphics card to overheat. When hardware overheats, your operating system automatically slows down performance to prevent damage — a process called thermal throttling. Cleaning out dust can restore full speed.

Shut down your computer completely and unplug it. Use a can of compressed air to blow dust out of the vents on the back and sides of your computer tower or laptop. Hold the can upright and use short bursts. For a laptop, blow air into the vents along the sides and bottom. Do this outside or in a well-ventilated area, as dust will scatter.

If you are comfortable opening your computer case, you can clean the fans and heatsinks directly with compressed air. If you are not, the external cleaning is usually enough. Do this every six months if you have pets or live in a dusty environment, or once a year otherwise.

Check your hard drive space and upgrade if needed

When your hard drive is more than 85 percent full, your computer slows down because the operating system has no room to write temporary files. If you have cleaned up programs and cache and your drive is still nearly full, you may need to add storage.

On Windows, right-click "This PC," select "Properties," and look at the storage bar under "Device and drives." On macOS, click the Apple menu, select "About This Mac," then "Storage." If you are above 85 percent capacity, you have a few options: move large files (videos, photos, backups) to an external drive, subscribe to cloud storage like OneDrive or iCloud, or install a larger internal drive.

Installing a new drive is straightforward on desktop computers but requires opening your laptop, which can be risky if you are not experienced. If your laptop is full, an external drive or cloud storage is usually the safer choice.

Frequently Asked Questions

How much faster will my computer be after cleaning it up?

Speed improvement depends on how much clutter you remove and what was slowing you down. If malware was the culprit, you may see a dramatic difference. If your drive was 95 percent full, freeing up 30 gigabytes can cut boot time in half. Disabling startup programs typically shaves 30 seconds to two minutes off startup. Most users notice a meaningful difference within a week of regular use.

Is it safe to delete files from the Temp folder?

Yes. Temporary files are meant to be deleted. Windows and macOS create new ones as needed. The only risk is if a program is actively using a temp file when you delete it, but this is rare and usually causes only that program to behave oddly, not your entire system. Using the built-in cleanup tools (Settings on Windows, Storage on macOS) is safest because they avoid files currently in use.

Should I defragment my hard drive?

Only if you have a traditional hard drive (HDD), not a solid-state drive (SSD). Most modern computers use SSDs, which do not benefit from defragmentation and can be damaged by it. If you have an older computer with an HDD, Windows includes a defragmentation tool under Settings > System > Storage > Optimize drives. Run it once every few months.

What is the difference between restarting and shutting down?

Restarting closes all programs and clears RAM, then boots your computer fresh. Shutting down does the same but also powers off the hardware. Both clear temporary memory, but restarting is faster. If your computer feels sluggish, restart it before running cleanup tools — this alone often improves performance noticeably.

Can I undo changes if I disable the wrong startup program?

Yes. On Windows, open Task Manager, go to the Startup tab, right-click the program, and select "Enable." On macOS, go back to Login Items and click the plus button to add it back. If you cannot remember which program you disabled, restart your computer and check if anything is missing or broken. Most startup programs are not critical, so disabling them causes no harm.