Popular IT support questions: Why do computers slow down?

We deal with all sorts of IT support questions here at Dave’s Computers in Hillsborough. One of the most common is why a computer starts off fast and slows down so much? If the hardware is still working at 100 percent, why does everything run so slowly? From doing a little research, this question is also a common one in the wider community so I’m going to answer it here for the benefit of all.

When you first boot a new computer, one of the best things about it is when it boots in a couple of seconds. Then, over time, it seems to take longer and longer to start. Loading programs or browsing the internet gradually gets slower too. But why?

Use it and lose it

Computer operating systems aren’t that efficient at managing space or working tidily. Windows is the worst for this but MacOS and Linux have issues too. Imagine a set of bookshelves in your room. You pick one book up to read it and don’t put it back in the same place. You read different books over a period of months and leave them in different spaces than you found them. After a while it takes longer and longer to find the book you’re looking for.

This is one of the reasons why a computer slows down. The bookcase is the file system on your hard drive and the books are the files it needs to work. Your operating system picks up a file, uses it and doesn’t always put it back where it found it, meaning it has to search for it when it needs it next time.

The more you use your computer, the more this happens. I use this analogy all the time when answering IT support calls about slow computers.

If you still use hard drives and not Solid State Drives, you can use defragmentation to tidy things up. This sorts out all those files and puts them back in a logical order so the operating system can find them quickly again.

  1. Select a hard drive in Windows Explorer.
  2. Right click and select Properties then Tools.
  3. Select Optimize and let Windows tidy your files up.

Do not use defragmentation is you’re using an SSD. It doesn’t work the same way and can shorten the operating life of your drive.


Many Windows programs love to add themselves to the startup menu as they think they are important. As Windows loads, not only does it have to load the operating system and your security software, it also has to load these programs too, just in case you want them. As users, we don’t always want that.

Fortunately, there is a simple say to control that and you don’t need IT support to do it.

  1. Right click on the Windows task bar and select Task Manager.
  2. Select the Start-up tab and click Status. This should sort Enabled and Disabled into order.
  3. Select a program you don’t want to start with Windows, right click and select Disable.
  4. Work through the list until only core programs and security software is left enabled.

Aside from adding themselves to startup, running too many programs at once can seriously slow things down. Having only those programs you need right now open gives them more computer resources to use. This helps them work faster.

Now you know how to open Task Manager, you can use it to see how many programs are running and what system resources you have left. Check the percentages of CPU, Memory and Disk at the top of each column in Task Manager. If you’re using a high percentage shut down some of the running programs you aren’t using right now.

Security software

Security software has to load with the operating system in order to work effectively. It needs to integrate into the OS in order to keep an eye on everything. Trouble is, some software can slow things down a lot. Some of this delay is inevitable, some of it is not. Some antivirus for example is notorious for hogging computer resources and being slow. Some products are not.

If you find your security software slowing things down find a replacement. There are dozens of very good products on the market. Some is free, some is paid for. Try a different program and see how it works on your computer. Some will make no difference while others can seriously speed things up.

Check out AV-Test or AV-Comparatives for the best antivirus products out there. I use these sites regularly to advise my IT support customers. Never use a computer online without security software. No speed boost is worth the risk!

Hoarding files

As we use our computers, we collect files. Whether that’s cookies, browsing history, downloads, movies, music or whatever. If we don’t spring clean once in a while, it slows the computer down as it has to search it all to find what it wants. If your computer is slowing down and you want to avoid a IT support call you should tidy things up a bit.

  1. Open Windows Explorer and select This PC.
  2. Look at your drive(s) and see what percentage is being used and how much disk space you have free.
  3. Right click a drive that doesn’t have much free space and select Properties.
  4. Select Disk Clean-up and let Windows analyze how much space it can save.
  5. Select all files taking up a lot of space in the results window and let it clean them.
  6. Repeat for any other drives you have that are nearly full.

I use a product called CCleaner that is very good at housekeeping. It’s free and very good at what it does. Try it.

Malware or virus

If you have deleted files, removed startup items, defragmented your HDD and had a general tidy up of your computer and it still runs slow, you may have an infection. Note I said may. One symptom of a virus is a slowdown of the host computer while it works to fulfill whatever purpose the virus is designed for.

Run a virus scan and then a malware scan using one of the recommended products listed above. Then run it again. Leave it overnight if you need to, but run the scan and allow the software to fix anything it finds.

Those are just some of the suggestions I make to my IT support customers when they ask about slow computers. If you can get into the habit of housekeeping every once in a while, your computer shouldn’t slow down all that much.

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