Hard Drive for Time Machine

[Nye]

I want to buy a hard drive for OS X Leopard's Time Machine program but I don't know how much memory I need for it. I have an iMac with a 160GB HDD and I have used 60GB of it so far. Would the LaCie 160GB Firewire Mobile Hard Drive be enough or should I buy a 320GB or even 500GB for that extra space?

 

[deadkenny]

That depends on how much data you produce. Time machine makes historical backups of your data. So each change will most likely somehow result in a copy unless Apple found a way to do smart binary diffs.
So when the amount of Data you have is more or less the same and only changes a little, then 160GB will be enough. If you have heavy changes, then you will need more.
When it comes down to what makes sense I would go for the HD which is lowest $/MB - so most likely the 500GB model right now.