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Configuring a Multiboot System

If your computer already has any version of Windows installed and you have a second disk partition available (or enough unallocated space to create a second partition), you can install a clean copy of Windows 10 without disturbing your existing Windows installation. At boot time, you choose your Windows version from a startup menu. Although this is typically called a dual-boot system, it's more accurate to call it a multiboot configuration, because you can install multiple copies of Windows or other PC-compatible operating systems.

Having the capability to choose your operating system at startup is handy if you have a program or device that simply won't work under Windows 10. When you need to use the legacy program or device, you can boot into your earlier Windows version without too much fuss. This capability is also useful for software developers and IT professionals who need to be able to test how programs work under different operating systems using physical (not virtual) hardware.

For experienced Windows users, installing a second copy of Windows 10 in its own partition can also be helpful as a way to experiment with a potentially problematic program or device driver without compromising a working system. After you finish setting up the second, clean version of Windows 10, you'll see an additional entry on the startup menu that corresponds to your new installation. (The newly installed version is the default menu choice; it runs automatically if 30 seconds pass and you haven't made a choice.) Experiment with the program or driver and see how well it works. If, after testing thoroughly, you're satisfied that the program is safe to use, you can add it to the Windows 10 installation you use every day.

Use virtual machines instead of hassling with multiboot menus:
You can create truly elaborate multiboot configurations using more than a decade's worth of Windows versions. But unless you're running a hardware testing lab, there's no good reason to do that. The much simpler, smoother alternative is to use virtual hardware that faithfully re-creates the operating environment.
We strongly recommend Microsoft's Hyper-V virtualization software, which is a standard feature in the Pro editions of Windows 8.1 and Windows 10 and on recent Windows Server releases.
To run Windows 10 on a Mac, try Parallels, available at http://parallels.com. For other operating systems, check out VMware (http://vmware.com), which offers excellent virtualization software for use on desktop Windows machines and servers, and the free VirtualBox package from Oracle (http://virtualbox.org).
Using any of these solutions, you can install even the most ancient Windows version. Backing up a machine's configuration and restoring it is as simple as copying a file. Legally, you'll need a license for every operating system you install in a virtual machine. If you have a license to use Windows for evaluation purposes, the option to run Windows in a virtual machine can be a lifesaver.

To add Windows 10 to a system on which an existing version of Windows is already installed, first make sure that you have an available partition (or unformatted disk space) separate from the partition that contains the system files for your current Windows version.

The target partition can be a separate partition on the same physical disk, or it can be on a different hard disk. If your system contains a single disk with a single partition used as drive C, you cannot create a multiboot system unless you add a new disk or use software tools to shrink the existing partition and create a new partition from the free space. (The Disk Management console, Diskmgmt.msc, includes this capability; to shrink partitions on a system running an older Windows version, you'll need third-party software.) The new partition does not need to be empty; if it contains system files for another Windows installation, they will be moved to Windows.old. Run Setup, choose the Custom (Advanced) option, and select the disk and partition you want to use for the new installation.

The setup program automatically handles details of adding the newly installed operating system to the Boot Configuration Data store.

And how do you edit and configure the Boot Configuration Data store? Surprisingly, the only official tool is a command-line utility called Bcdedit. Bcdedit isn't an interactive program; instead, you perform tasks by appending switches and parameters to the Bcdedit command line. To display the complete syntax for this tool, open an elevated Command Prompt window (using the Run As Administrator option) and type the command bcdedit /?.

For everyday use, most Bcdedit options are esoteric, unnecessary-and risky. In fact, the only option that we remember using more than once in the past four years is the command to change the text for each entry in the boot menu. By default, the setup program adds the generic entry "Windows 10" for each installation. If you set up a dual-boot system using two copies of Windows 10 (one for everyday use, one for testing), you'll be unable to tell which is which because the menu text will be the same for each. To make the menu more informative, follow these steps:

  1. Start your computer, and choose either entry from the boot menu. After startup is complete, make a note of which installation is running.
  2. Right-click Start, or press Windows key+X, and choose Command Prompt (Admin) from the Quick Link menu. Click Yes in the User Account Control box to open an elevated Command Prompt window.
  3. Type the following command: bcdedit /set description "Menu description goes here" (substitute your own description for the placeholder text, and be sure to include the quotation marks). Press Enter.
  4. Restart your computer, and note that the menu description you just entered now appears on the menu. Select the other menu option.
  5. Repeat steps 2 and 3, again adding a menu description to replace the generic text and distinguish this installation from the other one.

A few startup options are available when you click or tap Change Defaults at the bottom of the boot menu.

You can choose which installation is the default operating system (this is where descriptive menu choices come in handy) and change the timer that determines how long you want to display the list of operating systems. The default is 30 seconds; you can choose 5 seconds (allowing the default operating system to start virtually automatically) or 5 minutes, if you want to ensure that you have a choice even if you're distracted while the system is restarting. These options write data directly to the Boot Configuration Data store.

For slightly more control over the boot menu timer, use the System Configuration utility, Msconfig.exe. The Boot tab allows you to change the default operating system and set the Timeout interval in any amount between 3 and 999 seconds.

Installing Windows 10 and Linux in a multiboot configuration

It's possible to install Windows 10 and Linux in a multiboot configuration that works much like the Windows multiboot setup described on the preceding pages. You can set it up to use the Windows 10 boot menu, or you can use a Linux boot loader (most commonly, GRUB) if you prefer. The procedure is a bit more complex than the procedure for installing another version of Windows, and it varies somewhat depending on which Linux distribution you use and which Linux tools (such as partition editors, boot loaders, and the like) you prefer. It's generally easier to set up such a system if the Windows partition is set up first, but it can be done either way: Windows and then Linux, or Linux and then Windows.

An Internet search for "dual boot Linux Windows" turns up plenty of detailed instructions, and if you add the name of your Linux distribution to the search input, you're likely to find the specific steps needed to make it work with Windows 8.1 or Windows 10.

More: Windows 10 Tutorials