Stupid partition mistake

drumrocker365 · Feb 26, 2015

So, I got the stupid idea to try and partition my external hard drive so I could install windows 10. It said set it to active so I did. I decided not to install it after I set it to active. Is this harmful? If so, how do I set it back?

Thanks,
Christian

i7Baby · Feb 26, 2015

https://social.technet.microsoft.com/Forums/windows/en-US/af3a1e24-214f-4e0e-b917-9530a27534de/how-to-deactivate-an-active-partition -

1. Open Command Prompt.
2. Type: diskpart
3. At the DISKPART prompt, type: list disk (This command will list all the disks that you have)
4. In the next prompt, type: select disk # ( # means the number of the disk which contain the wrong active partition )
5. At the DISKPART prompt, type: list partition
6. Use the command: select partition # (# means the number of the partition that you want to mark as active)
7. Inactive the active partition with command: inactive

xcrossroadsx · Feb 26, 2015

i7Baby :

Slightly quicker, you can just type "select volume X" where X is the drive letter of the partition you marked as active after entering diskpart, then type inactive. Either way is just fine.

drumrocker365 · Feb 27, 2015

Awesome, thanks guys! I am wondering though, what exactly did that do? (Marking it as active).

xcrossroadsx · Mar 10, 2015

drumrocker365 :

Bit late, but you seem interested

On an MBR (master boot record) disk, if the disk has a bootable partition, it will be marked with an active flag. This active flag tells the BIOS where the code to start the boot process is located on the disk (in reality, the BIOS speaks to the MBR on the disk, the MBR points to the active partition which holds the volume boot sector, which will hold the code that will locate and launch bootmgr on Vista+ machines or ntldr on XP machines). Each MBR disk can only have one active partition, so marking a partition as active while another partition is active on the same disk will necessarily mark the old active partition as inactive. A disk with no active partitions can not be used to boot, however it will still have an MBR as the MBR has other necessary information about the disk (where partitions start and end, etc). Do note that all of this information is becoming less and less used as Windows 8 finally has native support for GPT (a different partition scheme than MBR) and the boot process is quite a bit different when it comes to the UEFI launching the code to start the boot process.

drumrocker365 · Mar 16, 2015

xcrossroadsx :

drumrocker365 :

Bit late, but you seem interested

On an MBR (master boot record) disk, if the disk has a bootable partition, it will be marked with an active flag. This active flag tells the BIOS where the code to start the boot process is located on the disk (in reality, the BIOS speaks to the MBR on the disk, the MBR points to the active partition which holds the volume boot sector, which will hold the code that will locate and launch bootmgr on Vista+ machines or ntldr on XP machines). Each MBR disk can only have one active partition, so marking a partition as active while another partition is active on the same disk will necessarily mark the old active partition as inactive. A disk with no active partitions can not be used to boot, however it will still have an MBR as the MBR has other necessary information about the disk (where partitions start and end, etc). Do note that all of this information is becoming less and less used as Windows 8 finally has native support for GPT (a different partition scheme than MBR) and the boot process is quite a bit different when it comes to the UEFI launching the code to start the boot process.

Thanks! Very informative. +1

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