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Old 09-17-2013, 06:33 PM   #16
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Originally Posted by pgmer6809 View Post
So the bottom line is:
1. If you have a 64bit OS you can use GPT disks. I am not sure if you need GPT support in firmware, i.e. UEFI. You might not.
2. GPT disks can boot in MBR mode.
3. I don't see any advantage to booting in UEFI mode frankly. Of course if you are running Windows8 you have to, but for any other OS why?

Be careful assuming too much from your one experience with GPT and UEFI.

1. A 32-bit OS can support booting from a GPT (using either BIOS or UEFI). Not all 64-bit operating systems support GPT booting with a BIOS (Windows doesn't support BIOS booting for GPT). Although they are not common, there are 32-bit UEFI systems that require a 32-bit OS. Windows 32-bit doesn't support UEFI booting or GPT.

2. This is true only if the computer's motherboard firmware supports BIOS booting. Some UEFI motherboards do not support BIOS booting from a hard disk. In that case the only way to boot is using an EFI system partition (the MBR boot sector is ignored). Some UEFI firmware can support an MBR with no GPT but it still ignores the MBR boot sector (and uses the EFI system partition).

3. At the moment you are probably right assuming that BIOS booting works on the motherboard. However, BIOS booting will be supported less and less as time goes on. Some new computers may not support BIOS booting, and even if they do that may not be tested very well. Of course, UEFI may turn into another VESA bus or RDRAM and fade away without really becoming popular.

The configuration that you have does not use or require the EFI System Partition, although it doesn't hurt to have one. You can install a boot loader such as GRUB 2 in the EFI System Partition and then have the ability to boot using either BIOS or UEFI. I'm assuming that your motherboard has UEFI firmware.

The computer landscape is much different now than when BIOS was first introduced. Computer retailers are the normal way to buy computers, so they are more likely to affect what boot methods and operating systems are supported. It is nearly impossible to buy a consumer computer without Windows or to get support for a different OS. Some business class computers support Linux, but they may be limited to a specific distro and version of Linux. I think that we are going to see a separation between embedded computers, consumer PCs and business PCs as time goes on. They may have vastly different hardware, operating systems, applications and prices. In a way that is a return to the past when we had that sort of separation. For a while the IBM compatible PC filled all three roles.

Where does Linux fit in? I think that we are going to eventually see "Linux computers" versus "Windows computers". I don't want that, but it seems to be likely. Windows computers are becoming less and less standard, and Linux is going to be challenged to keep up with the sheer number of hardware variations. What's really needed to avoid that is a universal instruction language for writing hardware drivers that are compatible with any OS. Microsoft doesn't want that, of course, for many reasons. UEFI tries to do something like that but its drivers (especially graphics) are much too slow to be used as a replacement for OS drivers. They are fine for booting.

One reason to use UEFI booting is to learn how and be prepared for the eventuality that BIOS booting becomes unsupported.
Old 09-18-2013, 07:09 AM   #17
Alien Bob
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Originally Posted by pgmer6809 View Post
I don't see any advantage to booting in UEFI mode frankly. Of course if you are running Windows8 you have to, but for any other OS why?
If your boot disk is larger than 2 TB, then UEFI boot is a requirement.

Old 09-18-2013, 03:07 PM   #18
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Originally Posted by Alien Bob View Post
If your boot disk is larger than 2 TB, then UEFI boot is a requirement.

Can you explain why UEFI is a requirement for booting Linux? (I know GPT would be a requirement, but why UEFI?)

As I understand it a GPT disk can/does have a 'compatibility' sort of MBR at the front, before the GPT tables.
So Grub could put its IPL there, the IPL could then load the rest of the startup part of Grub (Grub 1.5) from a small GPT partition at the front of the disk (grub_bios), and the Grub 1.5 can now load the rest of Grub (the Grub Boot loader) from the ESP. This would be the same Grub Bootloader that the UEFI would load from the ESP. (That is in fact what is happening on my 1TB disk. I don't know why the same thing could not happen on a larger disk, provided it is a GPT disk.)

Provided that Grub 1.5 can access the ESP (and I am not sure what the requirement there is; maybe the ESP has to be in the first 2TB of the disk, or maybe Grub 1.5 is smart enough to read GPT tables, I don't know) then there is no real need to have the UEFI access the ESP.
My thinking is that if the UEFI can get at the ESP to load the GRUB bootloader, then GRub1.5 can probably do the same thing.
Once the Grub Boot loader is executing, you can then load any OS the Grub Bootloader can see and handle.
Hence no need for UEFI to boot even for large disks. Just need GPT support in Grub1.5 which I think it now has.
Old 09-18-2013, 04:06 PM   #19
Alien Bob
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Actually you are right and thank you for pointing me; GRUB2 can boot a 3TB disk without UEFI, provided that:

1) your legacy BIOS recognizes the disk as a 3TB disk
2) the disk has a GPT table
3) you create a small "BIOS boot" partition at the beginning of the disk and set the "bios_grub" flag to "1" using gdisk or parted
4) you install GRUB2 as your bootloader. GRUB2 will recognize the bios boot partition and install itself to it

The full 3 TB (or any disk size > 2 TB) should then be available to the OS then, you can create further partitions the way you like it.
Note: theoretical wisdom only...

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