Grey drive block?

I'd just installed a large amount of new windows components, so my laptop wasn't in the greatest state of fragmentation. But running Defraggler to sort this out, as per usual, I noticed a few lighter, grey/blue set of blocks on the drive graphic map that aren't listed on the legend. What are these exactly?

(image attached)

Thanks!

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post-31438-1251656290_thumb.jpg

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Cheers!

I see it in the options now.

=]