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 Post subject: UEFI/GPT/CSM/MBR
PostPosted: Fri Jul 05, 2019 1:00 pm 
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In would like to learn a bit more about exactly what these acronyms actually mean. I caught this comment elsewhere:

"Make sure your system is utilizing the new UEFI platform rather than the old BIOS platform to take full advantage of the latest tricknology and all of its advantages. This means your system drive (where you install Windows) will have a "GPT" Volume rather than a "MBR" Volume. You'll have to boot into your UEFI interface, and turn off "CSM" likely under BOOT Options before installing Windows or directly afterwards as well as when you update your UEFI/BIOS. It's good to double-check the CSM setting stays off whenever you add another storage drive as well.
If you type "Disk Management" in Windows start menu search box, double click to open screen, right click on your system drive, select "Properties", and choose "Volumes" tab, you'll see either "GPT" or 'MBR" listed under "Partition Style".

I kinda/sorta that I ended up in MBR mode (the Mac side sees that). What does this all mean?


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 Post subject: Re: UEFI/GPT/CSM/MBR
PostPosted: Mon Jul 08, 2019 6:27 pm 
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In the beginning, IBM created the BIOS, and yea it was good. At around the same time IBM created the MBR, and yea it was good. And lo the PC compatible era was born.

But Intel, seeing that systems based around its hardware would soon exceed the limitations of BIOS and MBR, both designed in the 1980s, came up with EFI and GPT. And yea the modern PC era was born.

However Intel, knowing that people would want to run older operating systems on its new EFI, created CSM, the Compatibility Support Module, which is effectively a BIOS emulator that hides EFI from the operating system. With this people were able to run their existing operating systems until EFI-compatible operating systems came about.

GPT was a welcome replacement since MBR can only address a disk of a maximum of 2TB in size, leading to horrible messes of arrays >2TB being split into 2TB virtual disks and then glommed together at the application layer. Database administrators everywhere breathed sighs of relief. Or at least the ones who were also responsible for managing hardware did (while the slackers who don't deign to touch hardware were wondering what all the fuss was about).

EFI discards all of BIOS's 1980s era problems (e.g. at boot only 1MB is available for the OS to use, as the processor is running in 16-bit mode) as well as discarding the requirement to boot off an MBR volume (which, remember, is limited to 2TB). It also allows CPUs of any architecture, as Intel came up with it during their failed Itanium (commonly known as the Itanic) development & production push. Open Firmware implemented pretty much everything EFI does except for the pretty mouse-driven configuration that PCs get to deal with.

UEFI is essentially a later version of EFI. Apple got on board before UEFI was finalized and of course views it as a NIH (Not Invented Here) so it mostly ignores the UEFI group in favor of doing things its own proprietary way. Which is one reason Macs are becoming less compatible over time. The other reason is they create their own part#s for otherwise off-the-shelf parts that the manufacturers drivers won't recognize (because the numbers don't line up) leading difficulty running non-Apple OSes until some clever individuals modify drivers to recognize their stupid new part#s and sanity is again restored to the world. Until the next model comes out with different part#s and the process starts all over again.

Another interesting quirk of Apple's EFI is that everyone else in the known universe implements CSM as part of their BIOS. Apple, instead, installs it on the drive in a hidden partition (technically in unallocated space on one side of the "BOOT CAMP" partition they create). As you may imagine this makes moving to a new disk kind of, well, impossible. Why? Probably because CSM was Not Invented Here.


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 Post subject: Re: UEFI/GPT/CSM/MBR
PostPosted: Mon Jul 08, 2019 7:50 pm 
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Wow, impressive coverage MB, thanks! :)


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 Post subject: Re: UEFI/GPT/CSM/MBR
PostPosted: Tue Jul 09, 2019 5:46 am 
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Wow, GREAT write up MB, I thank you SO much. I take it that whatever BIOS is essentially software, hardware plays little role, correct? X at least at 10.12.x is EFI, correct (EFI partitions spotted on most HFS formatted volumes, right?)? Does EFI get along with GUID/GPT/MBR, os if the CSM needed? GUID/GPT and MBR are available to disk utility in setting up whichever scheme on any specific drive.

Here is where I cheated a bit. Given the procedures for setting up a drive to take win10 without BC doing any partitioning, I discovered if I made the target drive GUID/GPT, when I ran the installer, there was no drive name. Making it MBR DID give me a name so I was sure I had the correct drive. I assumed that doing that "clean" thing,the windows installer would know exactly what needed to be done. DU tells me that drive is still MBR. So I take it win10 is using a CSM to deal with the disk it's on, right?

Of course, why would I care? I'll never deal with even a T drive under win10. IF I was to restart the whole install process, I assume if I had the target drive GUID/GPT, it would stay that way and the only thing gained is access to larger drive space that I don't need in the first place. Correct?


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 Post subject: Re: UEFI/GPT/CSM/MBR
PostPosted: Tue Jul 09, 2019 2:52 pm 
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BIOS/EFI/UEFI is basically the firmware of the PC, it initializes the hardware before the OS takes over and acts as a middleman between the OS and the hardware in some respects.

I don't know precisely how your copy of Windows is dealing with the MBR disk. I believe it can still run in EFI mode and boot off an MBR disk without running through CSM, which, because CSM isn't simply an option in the firmware on Macs, is unavailable without using Apple's Boot Camp utility in macOS to setup the Windows partition for you. Because you didn't use Boot Camp CSM is simply not an option. It's not a feature Windows can install on its own (each copy of CSM is unique to each model or at least product family in Mac terms), nor is it something the Windows-based Boot Camp drivers install.


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