There are actually three states to consider:
- Hibernated. This is the most volatile state. When Windows comes back up, your desktop and running apps will be restored to the same state they were in before.
- Shut down, but with "fast startup" enabled. Windows will come back up as from a full reboot, but the filesystem is left in at state from which Windows can come back up with minimal initialization. Linux might allow read-only access to the filesystem in this state.
- Fully shut down with "fast boot" disabled. This is the only state in which another OS can have full access to the filesystem.
If you tell Windows to "Restart" rather than shut down, it
always does a full shutdown regardless of the "fast boot" option setting. Telling Windows to restart and then directing the reboot into Linux is another way to ensure that the NTFS filesystem is in a safe state.