Backup using LOADS of disk space - why?

I have a default backup set up on my computer, backing up the C: drive to the E: drive (partition).  I've been having some problems with disk space on E: so checked out the file named N360_BACKUP - seems it's about 63GB in size!  I was wondering  firstly, why the file is so big, what it is and if I can delete it.

 

When I open 'Computer', there is a Norton Backup Drive there which contains 'Default set on E:', so what is this extra file thing on E:?

 

Thanks to anyone who can help (I am a complete novice when it comes to this stuff...)

 

Sarah :)