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Slow running is a very common problem for computers and one which often needlessly leads to their early disposal. But there are many things described here that you can do, often quite simply, to recover lost performance.

Summary

This page gives guidance on how to diagnose problems causing a Windows laptop (or desktop) to run slowly, and what to do about them. Some of the guidance may be applicable to other operating systems (Linux, OS/X), particularly where it relates to hardware. Other ideas may not be directly applicable but may nevertheless inspire lines of investigation.

Safety

Before doing anything, it is vital that the user's data is backed up.

Consider anti-static precautions when handling RAM or deep disassembly, especially when humidity is very low, or at least touch an earthed metal object before starting.

Introduction

Probably the most common reason people ditch their old computer and buy a new one is not that the old one is broken in any way, but that it’s simply running slowly. There are plenty of suggestions online, as well as paid-for products, which claim to fix slowness. Many of these will make little difference and some may make the problem even worse or install unwanted programs. There are a few key things that are well worth trying before giving up on your trusty PC or Windows laptop (and many of these will work for Macs too), but before you attempt anything, it’s vital that you back-up your files.

Preliminary investigation

You should make few simple observations and tests before engaging on a "deep dive".

Check how much RAM installed. Windows XP needs at least 512MB and Vista or later should be given at least 1 - 2GB. (More than 4GB is simply wasted on a 32 bit operating system as it has no way of accessing it.) Upgrading memory is easy, but you must make sure you use the right type, and that more than one module form an acceptable mixture. (For example, it might be acceptable to add a 1GB module (1024MB) to a 512GB module, but not to a 256GB. Check online for the computer's user handbook if it's not to hand.)

If the computer is plagued by pop-ups then this is a strong indication of malware, or at least some very undesirable programs. Getting rid of these will be a priority. Antivirus software (if installed) may show it up as PUPs (Potentially Unwanted Programs).

PUPs are often installed by download sites, from which they make their money. Steer clear of these sites, and any sites which require you to install a "download manager". Always download programs from the developer's own or recommended site, and be very careful of pre-checked tick boxes offering additional "recommended" software or toolbars which are very rarely worth having.

If the computer is overheating (often indicated by the fan running continuously) it may be that the CPU speed has been automatically reduced to limit heat output. Cleaning the fan and air filters is required. Speedfan is useful for showing internal temperatures.

Running Task Manager (from the ctrl-alt-del menu) and sorting the display on the CPU column will indicate whether a particular program is to blame. This might be a browser or browser plug-in or some program which is running wild. Windows Update has sometimes been known to hog the CPU. (Windows Update is one of many system tasks which run in the svchost process, many instances of which will often be seen.)

Microsoft Sysinternals Process Explorer is an enhanced version of the standard Task Manager and and is well worth getting to know as it can give more detailed information than the standard Task Manager. In addition to CPU, see if any processes are doing a lot of I/O (input/output) or using a lot of memory (Private Bytes or Working Set). A very valuable feature of Process Explorer is that it can submit details of unknown processes to Virus Total to check whether they are known malware.

If the hard disk light is on for much of the time then this is likely to be a symptom of an underlying problem, though not of itself much of an indication of its cause. If it's a software problem then Process Explorer should show the offending process, but it could equally be an ageing hard disk - see Hardware.

Tcpview, also from Sysinternals, is another valuable tool which shows network connections and traffic across them. This could give a clue if Internet access seems very slow.

If the computer has low-end graphics then disabling some of the graphical features of Windows through Desktop Properties may help.

Viruses and antivirus software

Viruses or malware on your computer are very likely to slow it down, and worse, may be using your computer to distribute spam, phishing emails, or to conduct other illegal activities.

First of all, check that antivirus software is installed and is being regularly updated. (People often rely on the free trial antivirus that comes with their computer and don't realise that they're unprotected if they don't renew it when the free trial period ends.)

Check also that there is only one antivirus program running. If you have more than one they can fight one another, causing problems. If you want to change antivirus, always follow the sequence: (a) download new antivirus, (b) uninstall old antivirus and reboot, (c) install new antivirus and reboot again for good measure.

There are several lightweight, reliable and free antivirus offerings. Currently, Avast seems to work well but it does nag you to upgrade to the paid version. Sophos Home is quieter but the free version offers few options. This is an advantage for non-technical users but for a more advance user there is nothing to fine tune.

Some of the "big name" antivirus products (e.g. Symantec (Norton) and McAfee) are heavy on system resources. Go into the product's control panel and check the options. Consider whether it would be safe to use less aggressive settings. A full system scan should only be necessary if you have particular concerns, and if required, should be scheduled to run overnight.

If malware manages to gain control of your computer before your antivirus kicks in, it can often use stealth techniques to hide itself. One answer is to run an offline virus scan from a CD or USB memory stick independently of Windows – Sophos Bootable Anti-virus or Kaspersky Rescue Disk are possibilities.

Both Sophos Bootable Antivirus and Kasperky Rescue can be booted either from a CD or a memory stick. Kaspersky is easier to use as it runs from a graphical user interface and can update itself with the latest virus signatures from the Internet. It also allows you to browse the hard disk, and if necessary, save valuable files to a memory stick before proceeding. Sophos is character-based and has to be downloaded afresh to get the latest signatures.

An offline scan should only be used once the installed antivirus has been checked and run, and any malware deleted from quarantine, as there is a slight possibility of it causing more problems.

Background and startup programs

Having cleaned up any viruses and made sure your regular antivirus program is functioning and up to date, the next thing to look at is whether you have any unused programs installed or running in the background. You can do this to some extent from within Windows, but it's easier if you download the free version of CCleaner and run it.

Installed programs

In CCleaner, click the Tools tab on the left. The Uninstall button shows all the installed programs, which you should review. Uninstall any not needed using the Run Uninstaller button on the right.

Startup programs

Programs which start up along with Windows, as well as browser plug-ins, can really slow down a computer. The Startup button on CCleaner shows these start-up programs under Windows and browser tabs. It’s hard to give specific advice on what you can disable, but research the things you don't recognise using your favourite search engine and get rid of what you don't need. And if you’ve collected any of those pesky browser toolbars which come along for the ride, you can disable them too.

An alternative to using CCleaner for this purpose is Microsoft's MSConfig. To launch it, click Start → Run; in the Open box type msconfig; then click on OK or press Enter. Select the Startup tab.

The PACS-portal website describes other options on its Introduction page and offers details on all the programs which may start along Windows on its Database page to help you decide whether they are useful and safe or not.

Disk space clean-up

The Cleaner tab on the left of CCleaner allows you to delete temporary Windows and application files. This is unlikely to improve performance unless you are very low on disk space. You will probably want to take care not to delete browser internet history or saved passwords. If space is at a premium, consider moving infrequently used files to an external hard disk or cloud storage.

Registry cleaning

The Registry tab on CCleaner allows you to fix registry problems such as registry keys left over from a failed or incomplete uninstall. This may be worth trying, and indeed, there are plenty of registry cleaner programs out there which claim they will transform your life, but messing with the registry is never without risk and is unlikely to result in a major improvement. If you try it, be sure to select the option to back-up changes. This will create a file which you can simply double-click in order to revert the registry in case of problems.

Lightweight alternative programs

You may find you're only using a small fraction of the functionality of a particular application, in which case you may be able to find a leaner alternative. Try alternative.net, which allows you to search for an alternative or to browse a large database of applications of all sorts.

If you use Adobe Reader you can download a lightweight alternative such as Foxit Reader or SumatraPDF for viewing PDF files and then uninstall the Adobe offering. The same applies for video players. Media Player Classic is a lightweight alternative to Windows Media Player.

You may find that Opera or Chrome give better performance than other browsers, but most browsers can become slow with plug-ins, toolbars and "accelerators" or with many tabs open.

Hard disks

Software

We've already discussed disk space exhaustion above.

Defragging a disk is often quoted as a cure, but with modern disks, operating systems and the file systems they support it makes little difference. The only time when defragging is really necessary is if you want to enable hibernation for the first time and there is insufficient disk space in a contiguous block for the hibernation file.

You should never defrag a solid state disk (SSD) as it will make virtually no difference and only increase the wear level on all the memory cells.

Hardware

Modern hard disks store data at such high densities that they don't expect to be able to read it all back without error. See Advanced hard disk tools for further details. In brief, automatic retries and sophisticated mathematical error correction tricks are used to correct errors up to a certain maximum number of bits in a block, but these can take a significant amount of time and cause the disk to appear to freeze for as much as several seconds. And if all this fails, the disk has no option but to return an error, causing Windows to retry the read request several times before giving up. Clearly, poor disk health can have a major impact on performance.

Spinrite is a hard disk maintenance tool that can often speed up a hard disk by encouraging it to move data from error-prone areas of the disk to spare sectors.

Modern disks have their own built in health monitoring known as S.M.A.R.T., but unfortunately the health metrics and well-being criteria are not standardised across the industry. There are utilities for reporting S.M.A.R.T. data, which is not easily accessible under Windows itself. Speedfan has the advantage that it can interrogate a large online database containing real-world S.M.A.R.T. data from many other users in order to show how the health of your disk compares with others of the same type and comparable age. On the S.M.A.R.T. tab, select your hard disk from the drop-down list, review the data and then click "Perform online in-depth analysis". If the health appears to be poor, consider cloning the hard disk to a replacement.

Migration to a Solid Sate Disk (SSD) can make a very worthwhile improvement. This is fully discussed in SSD Migration and Troubleshooting.

Reinstall your operating system

If all else fails then the "nuclear option" of reinstalling Windows and all your programs and data will usually help.

However, if you’re still running XP then you’re living dangerously. Think about using Linux, a free and open-source operating system – there are versions that will run happily even on an old laptop from the last century. See Linux migration for further details.

For an unsophisticated user simply doing email, web browsing and maybe a little word processing, reinstallation should be fairly painless provided you have installation media to hand. Newer PCs often have a rescue partition on the hard disk which can be used to restore it to its original state.

Double-check that all user data has been backed up, including any locally held mail files, contacts lists and appointments.

If licence keys are not available, most can be found using the Magical JellyBean KeyFinder.

Before starting it's worth saving device drivers, particularly if installation media for peripherals such as printers, scanners, cameras etc is not available, or if using a generic Windows installation disk rather than one from the laptop manufacturer. Double Driver can be used to save drivers for reinstallation later. It's always preferable to download fresh copies from the manufacturer's website if possible but saved device driver files will get you out of trouble if you later find that any are no longer available.

Don't forget to reinstall antivirus software as one of the first things you do after getting Windows up and running. But first, uninstall any free trial antivirus that might come with a reinstallation from the PC vendor's installation media or recovery partition.

It will take some while and probably several reboots for Windows to auto-update with the latest patches. Wait until this is complete before using the PC in earnest or you may pick up malware and find yourself back at square one!

External links

• Cleaning and optimizing a Windows computer safely contains a wealth of information for in-depth cleaning of a Windows computer.
• How to mend a slow computer The Guardian, 16th June 2014