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Mark a partition as active (or unmark it so it isn't bootable)

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What is an active partition?

If a disk partition is marked as active then this tells the BIOS that the partition contains an operating system and can be booted from.

When your computer first starts up it will look for an operating system. The BIOS has rules for how it does this, the most notable of which is the "boot order" which is simply the order in which it considers devices. The other thing it considers is whether any partition found on those devices is marked as "active". If it is marked as active then the BIOS will attempt to boot from it (i.e. load an operating system).

If there is no operating system on the active partition then the BIOS won't look for another active partition it will give an unhelpful message such as:

No operating system found

So it is very important that you only mark a partition as active if you know it contains (or will contain) an operating system. This is normally done for you when you install Windows.

How to mark a partition as active

There are two ways to mark a partition as active:

  • The simple way using the Disk Management GUI
  • A more difficult way using the command line

Either of these can be used to mark a partition as active.

Using the Disk Management GUI to mark as active

Probably the simplest way is to use Disk Management.

  1. Open Disk Management

    The exact way to open Disk Management does vary slightly according to the version of windows, but this should be a good guide:

    Start → Control Panel → System and Maintenance → Administrative Tools → Computer Management

    and then you will find Disk Management under Storage.

  2. On the right hand side you will see a list of all the partitions (drives to Windows), and in brackets whether the drive is marked as Active (Windows may also show the drive it booted from as "Boot" rather than Active).

    Right click the partition you want to mark as Active and select "Mark Partition As Active".

Be aware that using the Disk Management GUI you can only mark a parititon as active but you cannot unmark it as active, for that you must use the command line.

Using the command line to mark as active

This technique uses the command line utility "DiskPart" to mark a partion as active.

  1. Start by running DiskPart.

    Possibly the easiest way to run this is "Windows key" + "R", which will open run a "Run" dialog, enter "diskpart" (without the quotes) and click [OK]. Windows User Account Control may ask you to confirm that you want to run this, select yes.

    You should now see a new window similar to the following:

    Microsoft DiskPart version 6.2.9200

    Copyright (C) 1999-2012 Microsoft Corporation.
    On computer: DEV6

    DISKPART>

    The version number, copyright years and computer name may be different for you.

  2. Now you need to identify which disk you need to work with. Type the command:

    list disk

    and this will list all the drives connected to your computer, eg:

    DISKPART> list disk

     

      Disk ###  Status     Size     Free     Dyn  Gpt

      --------  ---------  -------  -------  ---  ---

      Disk 0    Online      931 GB      0 B

      Disk 1    Online     1863 GB      0 B

      Disk 2    Online     4092 MB      0 B

      Disk 3    No Media       0 B      0 B

      Disk 4    No Media       0 B      0 B

      Disk 5    Online       14 GB      0 B

     

    DISKPART>

    In my case it is disk 5 that I wanted mark as active.

    If you are not sure which disk you want then Disk Management uses the same drive numbers.

  3. To select the disk enter the command:

    select disk 5

    Substituting the correct drive on your system. It was disk 5 for me, but it will most likely be a different disk number for you. Be very confident that you are selecting the correct drive - you don't want to end up deleting the partition that has Windows on it.

    DISKPART> select disk 5

     

    Disk 5 is now the selected disk.

     

    DISKPART>

     

  4. It is a partition which is set to "active", not the disk. To see the partitions on that drive use:

    list partition

    eg

    DISKPART> list partition

     

      Partition ###  Type    Size     Offset

      -------------  ------  -------  -------

      Partition 1    Primary    14GB     31KB

     

    DISKPART>

    Be aware that diskpart does not show whether or not the partition is already marked as active.

  5. Even if you only have one partition you still need to select it. If you have more than one partition then you will need to select which partition you want to work with.

    To select a partition use:

    select partition n

    so since in my case I only had one partition and that was the partition I wanted to use the command is simply:

    select partition 1

    eg.

    DISKPART> select partition 1

     

    Partition 1 is now the selected partition.

     

    DISKPART>

  6. To mark the current partition as active simply use:

    active

    eg.

    DISKPART> active

     

    DiskPart marked the current parition as active.

     

    DISKPART>

    You can then use "exit" to quit DiskPart.

How to unmark a partition as active

In the same way as you can use DiskPart utility to mark a partition as active, you can also use DiskPart utiliyt to unmark a partition as active. You cannot use Disk Manager to do this.

  1. Start by running DiskPart.

    Possibly the easiest way to run this is "Windows key" + "R", which will open run a "Run" dialog, enter "diskpart" (without the quotes) and click [OK]. Windows User Account Control may ask you to confirm that you want to run this, select yes.

    You should now see a new window similar to the following:

    Microsoft DiskPart version 6.2.9200

    Copyright (C) 1999-2012 Microsoft Corporation.
    On computer: DEV6

    DISKPART>

    The version number, copyright years and computer name may be different for you.

  2. Now you need to identify which disk you need to work with. Type the command:

    list disk

    and this will list all the drives connected to your computer, eg:

    DISKPART> list disk

     

      Disk ###  Status     Size     Free     Dyn  Gpt

      --------  ---------  -------  -------  ---  ---

      Disk 0    Online      931 GB      0 B

      Disk 1    Online     1863 GB      0 B

      Disk 2    Online     4092 MB      0 B

      Disk 3    No Media       0 B      0 B

      Disk 4    No Media       0 B      0 B

      Disk 5    Online       14 GB      0 B

     

    DISKPART>

    In my case it is disk 5 that was marked as active and I wanted to clear that. (It was a USB disk and I didn't want the computer trying to boot from it.)

    If you are not sure which disk you want then Disk Management uses the same drive numbers.

  3. To select the disk enter the command:

    select disk 5

    Substituting the correct drive on your system. It was disk 5 for me, but it will most likely be a different disk number for you. Be very confident that you are selecting the correct drive - you don't want to end up deleting the partition that has Windows on it.

    DISKPART> select disk 5

     

    Disk 5 is now the selected disk.

     

    DISKPART>

     

  4. To see the partitions on that drive use:

    list partition

    eg

    DISKPART> list partition

     

      Partition ###  Type    Size     Offset

      -------------  ------  -------  -------

      Partition 1    Primary    14GB     31KB

     

    DISKPART>

    Be aware that diskpart does not show whether or not the partition is marked as active.

  5. Even if you only have one partition you still need to select it. If you have more than one partition then you will need to select which partition you want to work with.

    To select a partition use:

    select partition n

    so since in my case I only had one partition and that was the partition I wanted to use the command is simply:

    select partition 1

    eg.

    DISKPART> select partition 1

     

    Partition 1 is now the selected partition.

     

    DISKPART>

  6. To unmark the current partition as active simply use:

    inactive

    eg.

    DISKPART> inactive

     

    DiskPart marked the current parition as inactive.

     

    DISKPART>

    You can then use "exit" to quit DiskPart.

Be aware that if you are using Disk Managment it won't display this change (even if you tell it to do a refresh). It will display the change after a reboot or after the drive has been removed and inserted (in the case of removeable USB drives).

These notes have been tested with Windows Windows 8 and Windows 7.

About the author: is a dedicated software developer and webmaster. For his day job he develops websites and desktop applications as well as providing IT services. He moonlights as a technical author and consultant.