File Storage and Maintenances 
Inside your computer is a data storage device referred to as a Hard Disk Drive (HDD). We call that drive C:\. I compare it to a 'file cabinet'. The data we store and the programs we install are kept in this 'file cabinet'. When we either turn off our computer close our programs, they are kept in the 'file cabinet' for use later. Just like a file cabinet, there are folders, and folders within those main folders and so on. In the folder are our files, data files, pictures files, etc..
Everything seems so organized within this system, 'not quite'. It starts that way, but as we open, use, and close our programs, things get messy. 
We double click the program WORD. Now the 'workers' (RAM-Random Access Memory) go to the file cabinet, find the folder named WORD, get the necessary files and provide us with what we requested (opening WORD). 
Note: Not enough workers (RAM) in the system, the longer it takes for things to happen.
We type a letter and 'save as' Letter to Bill. We specify for it to be saved in the folder 'My Documents' and in a sub folder named 'My Letters'. The we close the program either by going to FILE and choosing Close or by clicking the X in the uppermost right corner of the WORD program 'window'. Now the workers go to put the files away, but they might not put them back where they got them from, so they put them where ever there is some free space in the file cabinet. Now this is the beginning of 'Fragmentation'. There are a number of things that could interfere with this closing procedure. A file could get put 1/2 in one folder and 1/2 in another. This is referred to as a 'crossed link file'. On occasion a file could even miss the folder and just be a bunch of lost data in the file cabinet. This is referred to as a 'lost cluster or 'file fragment'. We use Scandisk to 'clean' these kind of errors from our file system. Disk Defragmenter is used to put all the files back into their correct folders and organize the file cabinet to help with speedy access.

Drive C:\ is our main storage device. 'Our File Cabinet'.
RAM is Random Access Memory and represents our 'Work Crew'.
Scandisk is a program used to check and clean the file cabinet.
Disk Defragmenter is a program to organize the contents of our 'File Cabinet' (Drive C:)
* Both the above programs are located in System Tools. START-PROGRAMS-ACCESSORIES-SYSTEM TOOLS.