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Why your computer is so slow and how to fix it

We’ve become so used to our computers just working that when they suddenly become sluggish, we find it incredibly frustrating. 

Modern computers are built to run many programs at the same time, however, this added complexity can make it difficult to determine what’s making a computer slow. Is it due to the amount of programs running, or is there another underlying issue?

Here, we’ll break down some common reasons why your computer might be running slowly and some actions you can take to fix the issue.

Your hard drive is too full

Your computer will either have a Solid-State Drive (SSD) or a Hard Disk Drive (HDD) for its internal storage. SSDs are considered superior to HDDs because they are more reliable, use less power, and can access data faster. For this reason, most new devices will come equipped with an SSD rather than a HDD, but some older computers (or some inexpensive newer machines), may still come with an HDD. ‘Why is this important?’, you might ask. Well, the type of hard drive you help determine what’s slowing your machine.

If you have a HDD that is over 80% capacity, then it’s likely that your PC is slowing down because it is running out of space to store data. When this happens, it’ll split up data and store it at different places on the hard drive, which is a process called ‘fragmentation’. When you next read the data, your computer has to search harder to find it and make sense of it. This process will be processor-intensive and slow your computer down. 

As time goes on, you may start to delete files from your computer because you no longer need that file or program, and this leaves a free space where that file once was. If you install a new large file, your computer may decide to use that free space for part of the new file, and another space for the remainder of it. This process can make more sense if you think about your hard drive as a library that is running out of shelf space for its books. If the library gets a new book, and this book is very thick, the librarian may struggle to find a slot in the bookshelf to put it.

The solution here is to either remove some books to make space (delete files) or split the book into parts and slotting the parts on different shelves. Your computer isn’t going to delete files without asking you, so the second solution is the favored one.

Defragmentation, or defragging, is the reverse of this, and the solution to this problem. When you defrag your hard drive, you are reassembling broken files into a complete file and storing it in one place as a whole entity. Defragging also rearranges the remaining free space on your drive into one block. We offer a defragging tool which has a free version - you can download Defraggler here.

Some programs are using too much memory

A common reason for your computer being slow is that it has resource-hungry programs installed, which are taking up a high proportion of its CPU and memory. You may also have programs running in the background that you aren’t even aware are running. Maybe programs have permission to open on startup, and even if you close the window they may continue to idly run in the background and take up resources.

You can identify if you have any problem programs taking up an unusually large percentage of memory and CPU by opening the Task Manager program. On all versions of Windows 7, 8 and 10, you can open Task Manager by holding Ctrl + Shift + Esc. This is known as a hotkey feature, and it will take you straight to the Task Manager window.

Once Task Manager is open, click the ‘CPU’, ‘Memory’, and ‘Disk’ headers at the top of the table to filter the programs in descending order based on their usage. If a program is using a lot of memory you can try and close it through the program’s interface, or by right-clicking on the program in Task Manager and selecting ‘End Task’. 

CCleaner can help you manage and improve your computer performance by letting you quickly and easily see which apps are automatically set to run at startup. Simply download CCleaner and go to ‘Tools’ > ‘Startup’ and you can disable the apps that you don’t need to run when your machine boots. CCleaner can also uninstall programs for you - even when the Windows applet says otherwise.

Your computer is infected with malware or viruses

Malware is software that is specifically designed to damage your computer or gather unauthorized information about your activity. Cybercriminals and hackers design malware for a whole bunch of reasons. Keylogger malware, for example, is designed to store every keystroke you make on your keyboard, save it in a file, and send that file to a server controlled by the hacker. Other malware is more obviously destructive, such as ransomware, which will lock your files and demand you pay money to the hackers in order to release them. 

You may have a virus on your computer if you are experiencing frequent error messages for an unknown reason, or if files that you don’t recognize are using a large amount of memory. Your computer can become infected in many ways, for example, by downloading software from untrusted websites or clicking on suspicious email links.

It’s strongly advised to have antivirus (AV) software installed to your machine, as well as practicing strong privacy in order to identify viruses and also protect yourself from further viruses. If you’re not running AV, download it now. Both Avast and AVG come out top in independent testing and are free to install and use.

You haven’t updated your software

You should always ensure that your operating system is running on the latest version available. Your computer should prompt you when a new update is available, but if for some reason it doesn’t, you can download the latest version of the update from the Microsoft website. 

Failing to update your computer can leave it vulnerable to viruses because updates usually provide fixes to known vulnerabilities. Hackers often rely on exploiting known bugs and targeting users, hoping that a good percentage of them won’t have updated their system to include the latest security patches.

While keeping your operating system up to date is essential, this logic applies to all software. You should ensure that your browser is running on the latest version and that your antivirus software is too. If you’re asking ‘Why is my computer running slow?’, the answer could be that your old software has left you vulnerable to a cyberattack, and you have been successfully targeted. CCleaner can make managing updates really easy by updating your installed software for you - in one go.

We recommend CCleaner to keep your computer safe and improve performance. CCleaner helps you browse more safely by erasing your search history and online trackers, can delete junk files that are using valuable space, update software, and help you to manage your PC so it can perform at its best. You can download CCleaner here.


  • Why is my computer so slow?

    Computers become slow for a variety of reasons, whether it’s an unnecessary build up of junk files and settings, too many apps running in the background, a fragmented hard drive or malware and viruses.

  • How do you fix a slow computer?

    You don’t have to resort to a brand new computer or hardware. There’s a lot you can do before reaching this stage. CCleaner can help you manage your PC’s processing power to unlock more speed, plus can save 34GB of free space each year.

  • How can you boost a PC’s speed?

    You can boost your PC’s speed by putting any inactive programs to sleep. CCleaner’s patented Performance Optimizer feature can do this for you automatically, making your computer run up to 34% faster. It then enables dormant programs when you need them.