You are advised to exercise caution while installing Windows 8 on a system with another operating system. Windows 8's new hybrid Standby mode (Hybrid Boot) really reduces the amount of time needed to boot the system, but in the process it makes changes that are not compatible with other operating systems. These settings may even prevent the other operating systems from booting.
Those who install Windows 8 on a hard drive that already has an operating system installed are safe. The set-up wizard detects the OS and automatically deactivates the Hybrid Boot. It is riskier to install Windows 8 on a separate hard drive and access other hard drives for data exchange. If an operating system does not exist on the second drive, Windows 8 also uses this drive for the hybrid Standby mode. So if you access the drive later with an older Windows system, it will recognise these changes in the file system and try to carry out a lengthy repair. Sometimes this may lead to loss of data.
Those who wish to install Windows 8 on a computer with several hard drives and operating systems should first take a backup of their data. Then, install the system on the same hard disk as the other OS or remove all other hard drives, execute the installation and then manually deactivate the Hybrid Boot. Only after that should you reconnect other hard drives and allow Windows 8 to access it. To switch off Hybrid Boot, open the Control Panel and click on "Hardware and Sound" and then on "Power options". Now select the link "Select what should happen after pressing the power switches".
The next dialogue box will show another link "Some settings are not available at present", which you must also click on. Now, you will be able to view the configuration options for "Shut down".
Here, deactivate the option "Activate Quick start" and confirm the changes with "OK". This ensures that the idle state remains in effect, but the PC always shuts down completely when you switch it off.
You can also make complete shut downs with the command "shutdown.exe /s /t ". However, this might be too risky for dual boot systems.