Time machine and backups question

Hi,

I'm new to mac and am having a little difficulty with the time machine backup system.
I have a 2011 MBP 15" standard spec

I have about 50GB of data on the 500GB drive but in time machine it says my backup would be 351GB.

And if i go into get info on Macintosh HD it tells me that i have 499.25 total, 448.87 available and 50.38 used, which is fair enough.

But if i go into storage info in about this mac it says i have 147GB free and that there is data to the tune of 301GB in the backups slice.

these add up to the 351GB that time machine is trying to backup but i haven't made a 301GB backup and cant find where this would be on the drive.

Can anyone shed some light on whats happening please?

Thanks

 

I think I worked it out, it said in time machine that it makes these snapshots hourly.

I disabled time machine in system preferences and the 301GB of purple backups vanished.

It seems that the built in time machine is not ideal for how i want to perform backups.

On my Vista laptop i have a program called vice versa which you make a script in a wizard with what exact files you want to backup and it compares and updates as necessary, pretty much like itunes does with the ipod, you update the source and the destination only updates the new info which is good as only the first backup takes a long time, subsequent ones dont.

I enquired vice versa for mac but was told its written in C++ so there is no chance.

Is there a similar program available for mac?

cheers