[CentOS] free space created during partitioning while installing CentOS5.5

I installed CentOS5.5 on Dell Inspiron N5010. During partitioning, when I
created swap = 6GB then additional 4MB free space was created and when I
created ext3 for linux=217GB, then additional 7MB free space was created.
Didn't understand why these 2 extra free spaces were created.
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