Microsoft released the 1st service pack for Windows 7, apart from combining all the previous updates into 1 package there are a couple of new updates included for improved reliability when connecting to HDMI audio devices, printing using the XPS Viewer, and restoring previous folders in Windows Explorer after restarting.
So apart from those 3 new updates, most computers should already have the rest installed, so it should be a small download of 40MB-100MB compared to 750MB for the full SP1 32-bit or 1050MB for the 64-bit download.
Having installed SP1 it only needed to download about 60MB for my computer and took about 20-30 minutes to install after several restarts, but if you are downloading the full amount it could take much longer.
Happy installing.
