Using the same Windows 8 Upgrade installer on multiple PCs

As per the article How the new Windows 8 license terms affect you:

You may transfer the software to another computer that belongs to you. … You may not transfer the software to share licenses between computers.

But what if I have a bunch of PCs with a mix of XP/Vista/Windows 7? Can I purchase either the Windows 8 Pro Upgrade $40 (download only) or $70 (DVD) version (both of which come without a key) only once and use it to upgrade all the PCs? Since I'm not sharing the license and each PC has its own valid genuine license, it should be allowed, right, or is it illegal? Even if they want people to shell out $40/$70 for each PC, how would they enforce the use of the installer/media on only one PC each?

I have been given to believe by a source that the installer will only check for the previous OS' key, which is what is confusing me (I have never purchased an upgrade version before this, only full retail or pre-installed versions). Is this true or will I need to enter two keys to make the upgrade work, one for the previous version and then one for Windows 8? If the latter is the case, then the issue is solved since obviously the same Windows 8 key will not be valid for multiple PCs.

Solution 1:

You could buy a blank or thumbdrive and use that create a bootable media using the $40 upgrade. You could purchase 3 licenses for $120. The Upgrade Assistant can create a bootable DVD if you want and you can use that same disc to upgrade multiple computers. When you make your purchase, you can specify the amount of licenses you want.

Step 1: Use the Upgrade Assistant to qualify the PC and pay the $40 (US)

Step 2: When the "Install Windows 8" message appears, select "Install by creating media" to create a bootable USB flash drive or an .iso (a disk image) file. Step 3: Wait for the Assistant to download the Windows 8 Pro installation package and create the bootable media or .iso file. The flash drive must be have 3GB or more of free space available.

Step 4: Burn the .iso file, if that's the path you chose, to a blank DVD. Step 5: Use that USB drive or DVD to boot the PC.

Step 6: When you get to the screen in Setup that asks, "Which type of installation do you want?' choose "Custom."

Step 7: Select a disk partition for the OS in the next screen. At this point, you can create a new partition if there's enough space available, or reformat the drive.

Step 8: Continue with the installation of Windows 8 Pro.

You don't need a separate disk for each machine to install the Windows-8 you have just need the license key which MS provide you via mail after your purchasing.

Source

Solution 2:

You need to buy a new licence for each machine you are updating.

The download or DVD comes with one licence for one PC.

When you upgrade you will be prompted for the licence key that comes with the software. You may well be able to enter it multiple times (to allow for reinstallation) but when it is activated Microsoft will check and mark concurrent usages invalid.

Solution 3:

You can use the same installer to upgrade multiple PCs but you do need different keys and the upgrade license permits you to upgrade one installation of windows to windows 8. So no, you can't use it to upgrade multiple PCs.

From that article:

Anytime you transfer the software to a new computer, you must remove the software from the prior computer.

Whether you can technically or not, it is against the terms and I'd be surprised if it continued working for very long.

Regarding your edit, as Joel Coehoorn says in the comments, you do need seperate keys for each install.

If you have a lot of PCs to upgrade, maybe Volume Licensing could be an option.