diskpart - detail partition Active flag missing

Railtech · 07 Apr 2021

So I had the need today to find what partition on a system disk was marked as Active. The installed Windows version is Windows 10 Pro 20H2 build 19042.867. I proceeded as I normally do opening an admin command prompt and running diskpart commands:

list disk
select disk
list partition
detail partition

In the past detail partition would display the Active flag as either Yes or NO. Now nothing, does anyone know what happened to this flag? Without it there is no way to know what partition on disk is active, is this an oversight by MS?

diskpart - detail partition Active flag missing-detail-partition.png

topgundcp · 07 Apr 2021

I think your disk is a GPT disk. There's no such thing as Active Flag. It's only applied to MBR disk.
Your 1st partition is MSR reserved partition, the 100MB(partition 2) is the EFI System partition.

Bree · 07 Apr 2021

Railtech said:

So I had the need today to find what partition on a system disk was marked as Active....
In the past detail partition would display the Active flag as either Yes or NO. Now nothing, does anyone know what happened to this flag? Without it there is no way to know what partition on disk is active, is this an oversight by MS?

No, its not an oversight. It is because the disk you are looking at is a GPT formated disk. There is no such thing as an 'active' partition for a GPT disk, that concept only exists for a Legacy bios/MBR system. A UEFI system always boots from the EFI partition.

And your partition 2 can be identified as an EFI partition on a GPT drive for two reasons, the first is that the 'Type' is given as a GUID string (on an MBR drive it is a two digit hex number) and the second is that it is 100MB, formatted as Fat32, which is typical for an EFI partition.

the GUID for an EFI system partition is C12A7328-F81F-11D2-BA4B-00A0C93EC93B.

GUID Partition Table - Wikipedia

Bree · 07 Apr 2021

topgundcp said:

I think your disk is a GPT disk....

Our posts crossed

Yes, the GUID of the EFI partition confirms that.

Railtech · 07 Apr 2021

Thanks all, come to think of it, I have not had need to look at Active partition since changing to GPT format. I had thoughts that this may be the reason but could not find anything to support that. You provided that.

zbook · 07 Apr 2021

See this link:

https://docs.microsoft.com/en-us/win...rtition-active

Code:

Active specifies whether to mark the partition as active. 
On a BIOS-based system, the active partition is the partition the system will boot to. 
This partition must be a primary partition.

On a Unified Extensible Firmware Interface (UEFI)-based system, this setting is not used. 
The system will always boot to the EFI System Partition (ESP). 
If Active is set for this partition type, it is ignored.

Only one active partition can be set on a hard disk. 
If an active partition already exists on the disk when this setting is changed to true, 
the existing active setting is removed and the selected partition is marked as active.

Only primary partitions can be marked as active. 
If Active is set for other partition types, the setting is ignored.