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I am able to install Debian 9.9. My query is: how does the Debian installer decide whether to use MBR or GPT? I don't see that option while installing Debian.

  • MBR and GPT refer to the way the disk will have a partition table, since the Debian installer gives you the choice when partitioning, it looks like you are asking the wrong question or, at least, a partial one. – Paradox May 11 at 9:10
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The type of partitioning to use is determined by partman-partitioning. The rules depend on the architecture; for 64-bit x86 systems, if the installer detects a Mac or an EFI (which means the installer was booted in EFI mode, not BIOS-compatibility mode), or if the disk to be partitioned is 2 TiB or more in size, it chooses GPT, otherwise it chooses MBR.

  • I don't understand the desire to cling to the old MBR partitioning scheme. Choose MBR by default, unless this or that or that, in which case choose GPT. Why even bother with this complex selection procedure, why not go straight for GPT? GPT is better than MBR in so many ways. What speaks for MBR other than fear of change? – Johan Myréen May 11 at 15:08
  • @Johan I suspect the main concern is ensuring that the installation is bootable. On Macs, or with an EFI boot, GPT is guaranteed to be bootable; in other scenarios it’s not. – Stephen Kitt May 11 at 15:43
  • Thanks for your comment, but I still don't see why GPT wouldn't be bootable even on a non-EFI PC, and how does it magically become bootable on a disk larger than 2TB? Grub knows what to do with a GPT disk, and with GPT you can avoid potential problems like storing boot code outside of partitions. I'm talking about Grub Stage 1.5 which is stored in a "no man's land" right after the MBR. – Johan Myréen May 11 at 16:06
  • @Johan I have a couple of non-UEFI PCs which ignore non-MBR disks when booting; so even though Grub can handle GPT, if the BIOS never loads the boot sector it’s not going to help much. I imagine there might be issues booting other OSs off a GPT disk on a BIOS system, even if Grub loads. – Stephen Kitt May 11 at 16:36
  • Most such problems can be worked around, but it’s better for most users if the installer tries to ensure the reboot won’t leave the user stuck... – Stephen Kitt May 11 at 16:39

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