Partitions. Unable to shrink. And what is this ?

I'm trialling W8.1 Enterprise and have run into something I don't understand regarding partitions.... here is what I did. 1/ I run the W8.1 installation and decide to format ALL partitions from the install disc. 2/ This seemed a good opportunity to rearrange things so I then went on to DELETE all the partitions so that I had 300Gb unallocated space showing. 3/ I install W8.1 onto this...