For those that have Windows 8 and want to upgrade to 8.1,,,,,, DON'T, just yet.
The update, at this time, is only available through the Windows app store and may be 3.5GB's in size.
Each of your computers with Windows 8 will have to download individually, unless you find a way to cache the download.
No ISO service pack download at this time. Maybe in a month that will change, or not.
Microsoft pisses off users, again.
The download itself may be a bit frustrating, though. The size of the update varies based on which version of Windows 8 you have installed, but it's generally about 3.5GB, so you'll want to have a reliable broadband connection.
Note, also, that the update has only just shipped, so Microsoft's servers are swamped and downloads may be slow going. Fortunately, you can keep using your PC while the files come down in the background and if the download is interrupted for any reason, you can pick it up from where it left off by starting the update again from the Windows Store.
Further complicating matters, however, if you have multiple devices to upgrade, you won't be able to download the update just once and apply it to all of your machines. El Reg asked Microsoft for clarification on this point and this is what we were told:
The Windows Store is the only way for consumers (non-enterprise, non-IT Pro) to download and install Windows 8.1. No ISOs will be made available, so each device needs to be updated individually via the Windows Store.
It actually goes further than that, though. "Consumers" here really means any copies of Windows 8 that weren't purchased through Microsoft's Volume Licensing programs. So a small business with 20 PCs to upgrade, for example, will have to do them one at a time via the Windows Store – so that's 20 separate 3.5GB downloads.