Will two OSes work on the same computer if they are on different hard drives?

by on March 31, 2010

Q: Will two OSes work on the same computer if they are on different hard drives? For example Windows 7 on one laptop and Windows XP on another?

One Response to “Will two OSes work on the same computer if they are on different hard drives?”
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    First you need to understand a little on how booting works. When your computer turns on the first main piece of software that gets to work is the BIOS. This is located on the motherboard. One very important piece of data kept there is your *drive boot order*. This is a list of drives (DVD, Hard Drive, USB, etc.) that the computer will work down until it finds one that is bootable.

    Once its finds a drive that is bootable, it reads the boot sector of the harddrive. This is a small block of data at the start of the drive that tells about the operating system or systems available. From here the OS will start loading or if there are multiple options a menu may get displayed.

    So, if you want a dual boot configuration where you boot to this menu and then make a choice of what OS you want to load up, both OSs need to have some data written to the boot sector of your main harddrive. You can still have that 2nd OS installed on a 2nd harddrive, but it won’t be truly independent. So if main harddrive died, and you removed it, you wouldn’t be able to boot from the 2nd harddrive, because the boot sector data for all the operating systems is on the main drive.

    Also, I’ve always found cleaning up the boot sector from a dual or multi boot setup to be a total pain in the neck. It’ an easy way to totally screw up a computer.

    That leaves you with two other options.

    1. Use some drive bays – Get two of those fast swap hard drive racks (example: http://www.newegg.com/Product/Product.aspx?Item=N82E16817993031 ). Install just one drive, install Win7. Then power down and swap drives in the rack and install your other OS.

    This keeps both OSes totally independent.

    2. Go Virtual. Install your main operating system (Windows 7), then install http://www.virtualbox.org/ (free). You can use Virtual box to have Windows XP or another operating system running within Windows 7, in its own Window.