I was having this same error 0xc1900101-0x20017 with my teen's computer. A nVidia 680i mobo with the first Intel quad-core chip. I mention teen since he likes to download risky software. A good sign of an infected computer is you have various toolbars installed on your system.
I was having some issues with System File Checker (sfc) but got those cleared up. I uninstalled stuff and ran Defender scans and CCleaner several times. The system apeeared to be working well and seemed to be virus free but no luck installing W8.1 without same ramdisk error reoccurring.
Solution: I installed W8 clean from DVD. Did the Media Center update, and then did the W8.1 update. I had absolutely no issues with the updates. The ramdisk error never happened again.
Moral of the story, I had remnants of a virus or malware somewhere that was affecting the update to W8.1. It wasn't drivers or anything else I found people suggesting to try on various web sites. You can't really blame your infected computer on Microsoft when you, or someone else using your computer, gives the malware or virus permission to install itself. In my case, it looks like Microsoft is off the hook since I had an infected computer preventing the W8.1 update from happening.