On Wed, 5 Apr 2017 16:13:44 -0500, Mark Lloyd
wrote:

On 04/05/2017 03:05 PM, wrote:

[snip]

Unless I read things wrong, UEFI doesn't look for or need the MBR.
No MBR on a GPT disk, for sure.


There IS a MBR. If nothing else, it has one unknown partition for the
whole drive (up to 2TB) to protect against old utilities. I don't know
if UEFI ever checks this unless you try to do a "legacy boot". This
would fail if only the protective partition is listed.

GPT drives tend to include a “protective MBR.” This type of MBR says
that the GPT drive has a single partition that extends across the
entire drive. If you try to manage a GPT disk with an old tool that
can only read MBRs, it will see a single partition that extends across
the entire drive. This protective MBR ensures the old tools won’t
mistake the GPT drive for an unpartitioned drive and overwrite its GPT
data with a new MBR. In other words, the protective MBR protects the
GPT data from being overwritten.

Note it says "tend to have" - it is not required and some OEM
installs do not have an MBR - if the drive is installed in a non-uefi
machine, the drive IS seen as unformatted..

Been there, wore out the Tee Shirt.