DIYbanter - View Single Post

Diesel

Wed, 05 Apr 2017 21:38:33 GMT in alt.home.repair, wrote:

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.

So you stated there was no MBR on a GPT formatted disk for what
reason, then?

--
I would like to apologize for not having offended you yet.
Please be patient. I will get to you shortly.