If you want to learn how to really clean a computer hard drive, then there are things you must do in order to make it a success and not have to turn around and do it again a few days later. First learn the things that can make it go slow. Some of these things are viruses, spyware and other general malware. These alone can gunk up your computer and make it go real slow more so than people think. You see many people think that viruses are not that bad. But the real truth is malware can account for almost 80 percent of computer slow down problems.
You need a few programs to make this happen for you. One program alone will not do enough. You need good malware protection. Fist get a good anti virus which is always updated and running all the time protecting your computer. Then you will want a good spyware program which will catch the rest of the stuff for you.
If you do not use anything now then you better start. This will always help you computer go faster. You can also get many good free virus programs not on the net so there is no excuses.
Now it also goes a litter farther than this too. Other things can also slow down your computer like bad drivers, a corrupt registry and more. You kind of want a whole suite of things to help you out. As fate would have it also, there are good free tools you can download on the internet to help you with this.
What you really need is a plan to keep your computer hard drive clean. Something like running everything once a month with a few programs will do the trick. Doing this every month alone can help keep your computer running faster and better all the time.