Just A Minute

Indeed, zipping (or RARing) any already-compressed format (MP3, JPG, DivX, WMV, Quicktime etc) will not benefit in size reduction.  In fact, compressing them again could actually increase their size.

In these cases, Zipping's benefit (as mentioned before) is to neatly gather them into a single object.  This is particularly useful if you have thousands of small files (e.g. 20K) you want to archive.  Note with zip that you can set the aggression of the compression, and in fact you can set it to 'store' (i.e. don't compress at all) and just gather the files into one container.

Also, because every file system have a minimum segment (e.g. 64K), any small file will be allocated at least one entire disk segment for storage, resulting in large waste of space (e.g. 64K of space minus 20K used = 44K wasted).  It's a bit like parking a mini in a parking space: there's empty space left in the bay, but it can't be used by anyone else.  By zipping many small files into one big one, there is hardly any wasted space on disk.

Also, copying and upload/download times are reduced because every file handled has a minimum amount of "housekeeping" processing required (opening file, closing file etc) which takes the same amount of time regardless of the size of the files involved.  The fewer the files handled, the less processing is required. 

Also, every time a new file starts copying/transmitting, its speed starts at a safe minimum and increases from there up to its maximum; especially with optical disks which take time to spin up to full speed.  Try copying 10,000 files of 10K each as opposed to one file of 100,000K - the speed difference is remarkable.

So Zip or RAR (which is similar to zip, but with a few neat benefits) is (as mentioned before) well worth mastering for transmitting or storing purposes.  And while Windows has Zip support built in, you get more control and power from a dedicated and free utility like 7-Zip (http://www.7-zip.org).

nylon@...