If you have a bootcamp partition on your Mac, you may notice degraded performance on Mac OS X. This could be because spotlight tries to index the bootcamp partition.
Simply change the spotlight preferences to not index the bootcamp partition by making it private. Here’s how to do just that:
System Preferences > Spotlight > Privacy then either click the
'+' sign and add your Bootcamp partition, or, if your Bootcamp Partition is visible on your desktop, just drag it into the Privacy section.