Disk Utility Problem/Question

[bearvsshark]

I have just erased my imac startup disk using the lion osx dvd and disk utility. I chose to do a zero pass format and after about 3 hours, it is done. When I click on the partition that was created though, it says there is 851.7mb of used space on the partition. I am confused since I formatted it, shouldn't there be no used space? Or is that 850mb being used for something that I can't prevent?

Here's a screenshot of my drive. Any help would be greatly appreciated.