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Make, Mark, or Set a partition or drive Active or Boot in Windows or Linux

Last reviewed: May 2010

On this page:

Facts you need to know about the Active or /boot partition

When you install an operating system (OS), the installation process usually and automatically sets a marker (just a one bit flag) near the start of the partition that will contain the boot files for that OS. When this bit marker is set (on) then that partition is the Active partition and can be bootable.

The partition (drive) marked Active should always contains the boot sector and boot files that will load an operating system (OS) whose operating files may be installed on that same partition, or on a different partition (even a Logical partition). Sometimes you need to change the location of the Active flag to a different partition. This most likely occurs when dual-booting, or recovering from a failed dual-boot installation, or when removing one OS from a dual-boot or multi-boot. The following characteristics apply

  1. Only a Primary partition (formatted) can be marked Active.
  2. Each hard disk should have one Active partition.
  3. The computer will boot from the first Active partition encountered (according to the disk boot order in the BIOS which is often user-changeable).

Just setting the correct partition as Active will not always make your computer bootable to the desired operating system (OS). Other items must also be in place.

  1. One Primary partition on the first hard disk (first in the BIOS disk boot order) is set as Active.
  2. The Active partition must then have a Boot Sector created by the desired operating system.
  3. This Active partition must also contain the Boot Loader and other Boot Files specific to that OS.
  4. The Boot Loader itself must know the correct physical location (address) of the OS.
  5. Finally, the OS's installed folders and files must be at that correct location on the hard disk.

Explanation:
During bootup, an Active partition is looked for on one of four possible Primary partitions on the hard disk first looked at by the BIOS (normally the first hard disk). The Boot Sector at the start of the Active partition knows which Boot Loader file to use and that's run if it's found on the Active partition. The Boot Loader knows the location of the OS (and other OSs in natural dual-boots) and passes control to the initialization file(s) of the selected OS at that location which then runs.

Windows and Linux use different terminology for the same bootable partition or drive

The term "active" is used for the bootable partition when you are in a Windows/DOS-type environment.
The term "boot" is used for the bootable partition when in a Linux environment.

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Use Disk Management if Windows 7, Vista, or XP boots, to make a Windows drive Active)

How to set the Active partition from a booted Windows 7, Vista or XP

This method will only allow you to make a Windows/DOS type of partition Active. It will not work with Linux partitions.

Caution: Using this method will make your computer unbootable if you make an incorrect Primary partition Active i.e. you will not be able to boot back to Windows to rectify the alteration you made.

Note: The warning you will receive from Disk Management is not entirely accurate. It should read "... . If the selected partition does not contain the boot files for an installed operating system, ...". It's the boot files that load the operating system which itself may be installed on a different Primary or Logical partition.
  1. Boot to Windows.
  2. Open Disk Management
    • In Win7 or Vista: Click Start > in the Search box, type diskmgmt.msc and then click the diskmgmt.msc higher up.
    • In Win XP: Click Start > click Run > type diskmgmt.msc and click OK > Select Disk Management.
  3. Right-click on the Primary partition you want to mark as Active and select Mark Partition as Active.
    Read the warning and click Yes to confirm your alteration.
  4. Restart computer.

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Use Diskpart command to make a Windows or Linux drive Active

How to make a partition Active using a Windows installation CD/DVD

  1. Bootup from any full Windows 7 or Vista installation DVD or even from NeoSmart's free Windows 7 System Recovery Disk or Vista Recovery Disk. All four perform identically in this situation. A Restore/Repair CD from an OEM is not sufficient.
    It must be a 64-bit version if a 64-bit Windows is installed.
  2. Select Repair your computer at the Install now screen.
    Click No if asked to Repair and Restart.
    Click Cancel if it looks for a Disk Image.
  3. Now in System Recovery Options,
    click the Command Prompt option.
    Press ENTER after you type in each of these commands which are not case-sensitive:
    • DISKPART     (to open the partition utility)
    • LIST DISK     (disk number(s) will be shown)
    • SELECT DISK n     (where n is the number of the disk - probably 0)
    • LIST PARTITION     (partition number(s) will be shown)
    • SELECT PARTITION n     (where n is the number of the Primary partition you wish to make Active)
    • ACTIVE     (the selected partition on the selected disk will be made Active)
    • EXIT     (to exit DiskPart)
    • EXIT     (to exit the Command Prompt)
  4. Restart computer.

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Use System Configuration (MSConfig), if Windows 7/Vista boots, to make a partition Active

How to make a Windows partition Active using the in-built MSConfig utility in Windows 7 or Vista

This method will allow you to make Active only a partition containing a Windows 7, Vista or Server installation.

Caution: Using this method will make your computer unbootable if the selected Windows cannot boot for a different reason i.e. you will not be able to boot back to Windows to rectify the alteration you made.

  1. Click Start , enter MSCONFIG in the Search box, and click msconfig up under Programs.
  2. In System Configuration, click the Boot tab.
    You will be presented with a list of available Windows installations.
    The installation currently Active is marked Current OS; Default OS.
  3. Highlight the Windows partition you want to be marked as Active.
    • Click Set as default.
    • Click Apply, click OK.
    • Click Restart.

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Use a GParted Live CD to make a Linux or Windows drive Active

How to use the free GParted CD to mark a Linux or Windows Primary partition Active.

  1. Download the lasest stable release of GParted
    and create the Live CD from the ISO file.
  2. Boot from the Linux Live CD and complete the three user-input requests.
    GParted will run automatically.
    • Right-click the Primary partition you wish to make Active
      and select Manage Flags.
    • In Manage Flags on ..., tick (to enable) the boot check box to make the partition Active.
    • Click Close and exit the partition utility.
  3. Restart your computer.

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Use a Linux Live CD to make a Linux or Windows drive Active

How to set the Active partition when Linux is running from a Live CD

This example uses Ubuntu 10. 04 Live CD. If using a different Linux distro look for the disk utility that comes with it - like Partition Editor, Disk Utility, Disk Editor, or similar. In this example you will actually be using GParted from the Ubuntu Live CD (as in the previous method).

  1. Boot from the Linux Live CD and run Linux from the CD ("Try Ubuntu ...").
  2. Click System > Administration > GParted.
    • Right-click the Primary partition you wish to make Active
      and select Manage Flags.
    • In Manage Flags on ..., tick (to enable) the boot check box to make the partition Active.
    • Click Close and exit the partition utility.
  3. Restart your computer.

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Use FDisk from booted Win9x/Me, or from 9x/Me floppy or bootable 98/Me CD/USB

Advanced users can mark a Primary partition as Active using a booted Win98/Me or 98/DOS floppy or CD/USB

The good old Win9x Startup Disk or MS-DOS Disk! Well, not so good any more. Sure, we can now run it from a bootable CD or USB Flash drive but, unfortunately, this Fdisk cannot correctly report the size of partitions greater that 64 GB! It attempts to do so, even for Non-DOS partitions like NTFS and Linux, but the sizes are totally incorrect (the Type and total Mbytes of a partition are very important for correct identification of a target partition). A WinMe floppy/CD is best (up to 137 GB) but is not faultless.

Nevertheless, some experienced users still find it convenient and useful. It's still quite accurate if you have just two partitions or if the partition is not very large, especially the tiny System Reserved partition in Win7 (normally just about 100 - 200 MB). It does allow you to mark a non-DOS Primary partition as Active.

  1. Open a MS-DOS Prompt in a Win9x/Me that's already running
    - or - boot from your Win9x/Me Startup floppy or bootable CD.
  2. Type FDISK at the prompt.
    Accept Y for "Do you wish to enable large disk support (Y/N)....?"
    Accept Y for "Should NTFS partitions on all drives be treated as large (Y/N)"
    • Type 4 to harmlessly Display partition information.
      Carefully read what's on the screen.
      If it's unclear to you, Press ESC twice to exit Fdisk now.
      Otherwise press ESC just once to continue.
    • Type 2 to Set active partition (you're on the FDISK Options screen).
    • Note which partition is currently marked A under Status (it's Active).
    • Enter the number that represents the partition you wish to be marked Active.
  3. Press ESC until out of Fdisk.
  4. Restart computer.

Recommendation: Don't use this method if targeting a large partition unless you have few partitions or unless you are experienced in such matters!

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Use Repair Your Computer from Windows 7 or Vista DVD

How to make NTFS, FAT32 or FAT partition Active using Repair Your Computer

Running "Repair your computer" after booting from the Win7/Vista DVD will not alter the Active location. Selecting Startup Repair on a second repair run still does not alter the Active location.

However the second run will add the required boot files (including bootmgr and Boot folder) to the currently Active partition and will boot Win7/Vista from that partition! That's not very satisfactory but at least you can now boot to Win7/Vista and use Disk Management to make the correct partition Active again, and then you're fine.

  1. Boot a Windows 7/Vista installation DVD or even from NeoSmart's free Windows 7 System Recovery Disk.
    It must be a 64-bit version if a 64-bit Windows is installed.
    • Press a key when you see Press any key to boot from a CD or DVD.
    • Select your Language and then Time....
    • Select Repair your computer (bottom left of the Install now screen).
      An automatic check of your system will run.
    • Click Repair and restart
  2. Bootup again from the same CD/DVD
    • Select Repair your computer again.
    • In System Recovery Options, select Windows 7/Vista, and click Next.
    • Click Startup Repair.
    • Click Finish when it's complete, and then Restart.
      Windows 7/Vista should boot normally.
  3. Open Disk Management in Windows 7/Vista (right-click Computer, select Manage, click Disk Management).
    • Right-click the Primary partition you wish to mark as Active,
      and select Mark Partition as Active. Read the warning and click Yes to confirm your alteration.
  4. Restart computer.

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Use a second computer

How to make the required partition Active on a second computer

Some users will have access to another computer and can transfer the hard disk to it. Then they can make the target partition Active from there before returning the hard disk to its original computer.
 

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Please remember that you alone are responsible for the consequences of any changes you make to your computer hardware or software.

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