Remember the HiRen's boot CD?
This was a self booting Windows OS project that booted the OS directly from CD and contained a lot of utilities, tools and hardware drivers. It was very useful for testing, diagnosing and repairing a PC. Fixing HD issues, removing malware and viruses and running benchmarks.
There haven't been any official HiRen's releases since 2012, but I just discovered the community decided to resurrect the project recently. It now runs a self booting Windows 10 64bit PE (preinstallation environment).
They seem to be keeping it fairly up to date which is useful for virus and malware removal.
https://www.hirensbootcd.org/