What's the difference between all the Ubuntu ISO downloads?

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http://askubuntu.com – I just got a new ThinkPad X230, 4 Gigs RAM, core i5 processor (3210m), and Windows 8. I wish to dual boot it with ubuntu 12.04.1 64 bit. I got the release page but it's got several links for downloading ubuntu, also the links are a bit confusing. What is MAC-amd64 for? And what's the difference between desktop and alternate download? The release page: http://releases.ubuntu.com/precise/ (HowTos)