i was almost sure that this was a download or application from the Apple website, but i couldn't find it. it's basically the windows desktop - start toolbar and everything - on my Mac.
Macs don't usually come with windows installed, did you buy it used?
Call apple tech support. Their number is on their website apple.com they should be able to figure out how that happened and what needs to be done to reverse it and gget the mac os back.
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