Lenovo ideapad 100S-11IBY User Manual page 21

When do I need to change the boot mode?
The default boot mode for your computer is UEFI mode. If you need to install a legacy operating
system, such as Windows, Linux or Dos, etc. (that is, any operating system before Windows 8)
on your computer, you must change the boot mode to Legacy Support. The legacy operating
system, such as Windows, Linux or Dos, etc. cannot be installed if you don't change the boot
mode.
Getting help

How can I contact the customer support center?
See "Chapter 3. Getting help and service" in the Lenovo Safety and General Information Guide.
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Chapter 4. Troubleshooting