I've seen that few years ago on some machines I bought for my job. 
I bet it was Dell Poweredge servers. Dell likes to have its own OS 
installed for maintenance purpose. If you don't care the maintenance, 
you can overwrite it, but why not dual boot? Maybe they offer that on 
laptops. Actually, if you buy a Dell computer "without OS", it certainly 
means "with FreeDOS".

     Didier