bcdedit.exe weigert sich, den Systemspeicher zu öffnen

Sieht aus wie OS X einige Änderungen vornimmt, die inkompatibel sind und bcdedit beschädigen. So konnte ich dieses Problem vorübergehend beheben: Setzen Sie das NVRAM mit ⌘+ Alt+ P+ zurück R, und starten Sie es direkt in die Windows-Partition, indem Sie halten Alt. Ich konnte Windows-Updates installieren, aber nach dem Booten in OS X und dem Installieren von Updates wurde bcdedit erneut beschädigt.

A Does Windows store actual BCD somewhere else? How does windows know on which partition and path to look for system BCD store?

EFI mode works with two legs;

1- a special BIOS (on chip writable area) partition where OS Loader Partition GUIDs are saved.
2- a system (hidden) partition with that GUID named EFI where Bootloader executable located (.efi extension files).

If you have installed/reinstalled several OS'es on EFI mode, then chances are, BIOS SPI chip got cluttered with many records of old OS'es and eventually filled up space on that special 8MB (if I'm not wrong) on-chip partition and became read-only.

Microsoft has a Technet page where it's shown how to clean up EFI duplicate or unneeded guid records (for example OS deleted but EFI record is still there) .
It involves creating a backup of current configuration then resetting it without duplicate records.

on an elevated cmd prompt;

Bcdedit /export savebcd 

this will backup current bootloader configurations.
make a copy of it for recovery purposes (savebcd will be our backup);

Copy savebcd newbcd 

Then export current records to a text file in human-readable format;

Bcdedit /enum firmware > enumfw.txt notepad enumfw.txt 

Load that file with notepad and review it to point duplicate records.

to delete each duplicate/obsolete record:

Bcdedit /store newbcd /delete 

where 93cee840-f524-11db-af62-aa767141e6b3 is just an EXAMPLE guid
replace it with the guid which you think unneeded

once you have gone thru deletion of all unneeded guids;

Bcdedit /import newbcd /clean 

Clears current EFI records and imports the cleaned (file we just cleaned unneeded records from) configuration data.
If you still get "A device attached to the system is not functioning." error,
Then; I don't want to be a bad news bringer but You have two paths to follow;
- Stick to your current system; make a WHOLE disk image backup (including your EFI partition) ASAP, because most possibly your SPI (BIOS) chip has cluttered and you cannot flush it without reflashing/replacing it.
This means current Bootloader pointers on the chip are final and if you try to reinstall another OS in EFI mode, it simply won't finalize installation and installer will be interrupted with an error (Windows OS family) or will finalize but BIOS won't load it (Linux installers, e.g. openSUSE), moreover you'll lose your old config, you'll end up having no booting OS on your device.
- Considering you have a Mac, ask tech support to reflash/replace BIOS.
if that's not the case or not feasible; replace hard drive switch to legacy BIOS mode (if that switch in BIOS still works, for me it just didn't work (Lenovo Ideapad B50)

other than these there are some other options to be ruled out as follows: as they are offered as if they are safe tips in some videos on Youtube about this subject, so I just mention them as not to try, because they are dangerous and/or voids device warranty (removing laptop battery + disassembling device to expose motherboard then removing bios battery + waiting (hoping) bios to reset, or shorting (short-circuiting) SPI chip); especially bios battery removal method never works in most (if not all) laptops, while shorting SPI chip can cause even whole system to get bricked.

Hope these helped.