1. Trying with USB drive or mounting the ISO. Same results. The update doesn't show up in the store.
2. Nope. Trying to install regularly.
3. I Installed Windows 8 From USB drive. Fresh install.
4. DIY PC, processor is AMD Opteron 185.
As the 2 replies above added, all AMD Athlon 64, FX, Opteron 1xx, 2xx and 8xx (as far as I could check) don't have CMPXCHG16b instruction set and therefor do not support Windows 8.1. Again, Windows 8 works perfectly.
In all versions up to Windows 8 (apparently) there was a workaround by Microsoft that was implemented in the OS (Software solution) to support 16bit compare (CMPXCHG16b) instruction set.
I wanted to know why it was omitted from Windows 8.1 and what are the benefits of removing such workaround.
I was looking for some blog post, a KB article, something to ease my mind.
Of course those systems we are using are 8 years old by now and dropping support for them was an inevitable move that was bound to happen some day. I just didn't expect it do come with a minor version upgrade!
My system with Windows 8 running on AMD Athlon 64 4000+ had the same issues. I read in another thread on a different site that 8.1 will only work if installed as 32 bit on these older processors. It's a shame, but worth considering.