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Dual boot: Two operating systems on one computer

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Dual boot: Two operating systems on one computer

In short: Two operating systems (for example Windows and Linux) are installed on one computer, and at startup you choose which one is loaded.

In more detail: With dual boot the systems share the same hardware but not at the same time: you start either one or the other. Each gets its own partitions. A boot loader (for example GRUB or the Windows Boot Manager) shows a menu at power-on. This is more powerful than a virtual machine because the system has direct access to processor, graphics card and memory.

In Depth

Preparation

  1. Back up all important data (mistakes when partitioning can delete everything).
  2. In Windows turn off fast startup and, with BitLocker encryption, note the recovery key.
  3. In Disk Management shrink the Windows partition to create unallocated space (at least about 30 to 50 GB for Linux).
  4. Create an installation stick of the Linux distribution.

Installation

Boot from the stick (boot menu, usually F12, Esc or F2). In the installer choose “Install alongside Windows” or create partitions manually in the free space (root /, optionally /home and swap). An entry is added to the EFI system partition. Do not reinstall Windows afterwards if Linux is already there, since Windows usually overwrites the boot loader.

Boot loader and problems

GRUB usually detects Windows automatically (os-prober). If you see only Windows after a Windows update, a restart from a Linux stick and sudo update-grub or the entry in the UEFI menu helps. Secure Boot is supported by the large distributions. Unfamiliar: Windows stores the hardware clock in local time, Linux in UTC; the time offset can be fixed with timedatectl set-local-rtc 1.

Sharing files and alternatives

Linux reads Windows’ NTFS partition; conversely Windows needs extra software for ext4. A shared data partition with exFAT or NTFS makes exchange easier. Whoever just wants to try things uses a live stick, WSL (Linux under Windows) or a virtual machine. On a separate second disk Windows stays untouched; that is the safest dual-boot variant.

See also: Trying out Linux, Boot process, NTFS, FAT32 and exFAT, BitLocker

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