Yes, it depends on what file you have.

Multimedia files are usually encoded in a very compressed format and compressing it again won't help to reduce the file size much.

On the other hand documents like XLS or DOC can be compressed really a lot.

It really depends on the file type

How compression works? Basically by reducing repititive information.

Try duplicating a line "Lowyat.NET rocks" in notepad for 5000 times. The file size might be big but once you compress it the file size will become probably thousand times smaller.

How it works? There are various methods ; give you an easy-to-understand example, it could be the compressed file just stores "Lowyat.NET rocks * 5000" and processing will be done when you uncompress the file.

For encoded video files like RMVB, it is already encoded using other algorithm such that repeated information has been reduced to a very low level, hence when you compress it again you won't get much reduction in file size.

If you are really interested in knowing, why don't read wikipedia?
http://en.wikipedia.org/wiki/Data_compression

Did you mean after extracting out the files from the ISO it goes from 1GB to 4GB?

This post has been edited by samurai1337: May 19 2006, 09:10 AM