Looks like there's THREE different downloads. one from Windows Update, one that's for downloadable for IT Professionals, and a downloadable ISO. The Windows Update one can be as little as 69 MB. I guess the installer checks to see if you've already updated for some of the components. The IT one is 316 MB The ISO one is 545 MB I like having a copy of service packs on my hard drive to use when I reload. I started with downloading the IT one. Now I'm leaning towards the ISO one. Bigger's better. Just thought I'd let everyone know about the choices.