Why is my Windows computer running slowly?

On this page:

• Computer always on
• Unneeded programs
• Insufficient RAM
• Defective or incompatible RAM
• Hard disk errors
• Fragmented hard drive
• Overheating CPU

Computer always on

If you usually leave your computer on and don't restart it very often, the Random Access Memory (RAM) can become full. Applications do not have space to function freely, and you may then see both a significant slowdown in performance and perhaps "out of memory" error messages. Simply restarting your computer should flush the RAM and speed up the computer.

Unneeded programs

If your computer is still running slowly, you may need to free some space on the hard drive by removing unneeded programs; see In Windows, how do I uninstall programs?

Insufficient RAM

UITS recommends the following minimum amounts of RAM, depending on your operating system:

These limits are much higher than those suggested by Microsoft, but are more realistic.

Defective or incompatible RAM

In most cases, a computer with either defective or incompatible RAM will simply not function. Other times, it will give clear and unambiguous blue-screen errors. In a few cases, the computer will function, but badly. The fix is to identify the incompatible or defective RAM and replace it. The best thing to do is to identify the proper amount of RAM for your computer and use only that, and, when problems occur, to run burn-in tests (some free ones are available for download) to ensure the RAM is still physically good.

Hard disk errors

Your disk may contain errors (e.g., file allocation errors), which can cause error messages as well as slow performance. To fix these errors, run ScanDisk.

Note: Be sure to run ScanDisk before you run DEFRAG or the Disk Defragmenter. ScanDisk will mark all the bad sectors on the disk; if you run DEFRAG or the Disk Defragmenter before ScanDisk, it might move good information into a bad sector, causing the information to be lost.

To run ScanDisk from Windows 2000, XP, or Vista:

1. Double-click My Computer.
   
   
2. Right-click the icon for the drive you want to defragment (usually (C:)), and then select Properties.
   
   
3. Click the Tools tab.
   
   
4. In the "Error-checking" section, click the Check Now... button.
   
   
5. Check the Automatically fix file system errors and the Scan for and attempt recovery of bad sectors boxes, and then click Start.
   
   
6. A dialog box will appear, saying:

   "The disk check could not be performed because exclusive access to the drive could not be obtained. Do you want to schedule this disk check to occur the next time you restart the computer?"

   Do not worry; this is expected behavior. The C: drive is busy because Windows is running, and the scan runs best before Windows loads. Simply click Yes to schedule the scan, and then restart the computer.

Fragmented hard drive

A fragmented hard drive will make the computer search the hard drive to find pieces of files. Fix this by using a defragmenter; see In Windows 2000, XP, and Vista, how do I defragment my hard drive?

Overheating CPU

Every Pentium-class and newer computer has fans and heat sinks specifically for cooling the CPU. When the fan wears out or becomes ineffective because it's clogged with dust or other debris, the temperature of the CPU rises. In most cases, the computer simply stops operating, but in some cases, the whole computer will appear to be running slowly or taking long pauses. Often this happens because the CPU is repeatedly locking up for a few seconds at a time. Sometimes it happens when the CPU is running just hot enough to affect its performance but not hot enough to lock up. Either clean the CPU fan so it spins at the proper rate, clean out the heat sink so it dissipates heat properly, or replace the fan/heat sink unit.

Also see:

• In DOS, what does the CHKDSK (check disk) command do?
• In Windows 2000 and XP, what is Disk Cleanup?
• In Windows 2000, XP, and Vista, how do I defragment my hard drive?
• In Windows XP, how can I work with compressed folders?