On linux, you can check this via the `gdisk` tool which should be available for any distro.

 gdisk -l /dev/sda

Here, `/dev/sda` is the device node *of the physical drive*, not a partition (`/dev/sda1`, `/dev/sda2`, etc. are partitions).

If you see something that includes:

 ***************************************************************
 Found invalid GPT and valid MBR; converting MBR to GPT format
 in memory. 
 ***************************************************************
You have a MBR style disk. Don't worry, this did not do any harm. 

If you don't see this warning, you have a GPT disk, or a *[hybrid GPT/MBR][1]* disk. The later are used mostly on Apple machines intended to dual-boot versions of MS Windows which do not support GPT. `gdisk` will indicate this with:

 Found valid GPT with hybrid MBR; using GPT

They may also be used in other situations where support for both styles is required.


 [1]: http://www.rodsbooks.com/gdisk/hybrid.html