operating system and design theory

Hello,
I'm looking for some books on OS design theory. I'd really like to get a 
minimal version of the OS running, if possible. Any help here would be 
amazingly awesome. :)
I haven't seen books on bookshare; I'm looking for something that will explain 
different approaches and all that.
Also: Does someone have accessible coppies of the intel manuals?
The ones I seen were in pdf. :(
thanks,

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