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Scandisk and Disk Defragmenter - What it is for
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Let us look in more detail at each of these points in turn:
- Mis-written information: this typically happens when the computer crashes. The information in working memory (RAM) is not properly written to the storage memory (HDD). There can be other causes too, such as badly written software, corrupt system files, etc. However, crashes are the major source of this mis-writing. The two most common problems that arise are:
- Lost (Orphaned) File Fragments: The computer cannot properly locate some of the information which has been written to the disk. N.B. This is not the same as "disk fragmentation" which Defrag deals with. (more later).
- Cross-linked Files: Two or more files have become entangled with each other.
Scandisk is the tool which addresses these problems, but it does not always make a good job of it! (More later). In this section, also, we are only really dealing with Windows Scandisk as a general maintenance tool; a DOS version of Scandisk runs routinely after a bad shutdown. More information about how best to manage this tool will be posted soon.
- Physical Damage to the Disk The disk is magnetic and this can be damaged by exposure to magnetic fields or through corruption over time. The heads can touch the surface of the disk and scratch it much like the old-fashionned gramophone needle could scratch the surface of a record. This latter problem is very serious and would likely necessitate buying a new HDD! Suffice to say, do NOT move your system unit while it is switched on! Physical damage to the disk is also addressed by Scandisk, but only when the "Thorough" option is selected (more later).
- Disk Fragmentation When, for example, you are writing a letter on your word processor, the computer does not know in advance how long your letter is going to be and thus how much space will be needed to store it on the hard disk. What your computer does is to find an available space on the hard disk, whenever you save the letter you are writing, and then record the information there. As you carry on typing in your letter and carry on saving it as you go along (as you should always do), the size of your document may grow too large for the space on the disk. The computer thus has to find another space somwhere else on the disk and store the next part of your letter there. The net result is that your letter, which, as far as you are concerned, is all one document, is infact split up among several areas on the hard disk. This process is called "fragmentation". It is as if you stored the various pages of your letter in different parts of your office because you ran out of room to store them in one place (although this is of course unlikely!).
This is where disk defragmentation comes in. It is a process whereby you can easily re-organise the files on the hard disk drive so that they are not split up and spread all over the place. It is in principle no different than your occasional re-organisation of your filing cabinet.
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