UEFI and the GPT

As I said in my previus post, I've not kept myself much up to date with the evolution of hardware for the last decade, so I had missed another huge change (not so noticeable as the SSD-NVMe thing, but highly important anyway). I'm talking about the modern UEFI and GPT partitions vs the old BIOS and MBR. You can read a short and clarifying article here.

In the past, we had the BIOS and in order to boot our OS's it needed a MBR in the first sector of the disk. This MBR could store information of up to 4 primary partitions as long with the boot loader. In order to have more than 4 partitions you needed to set one of those partitions as an extended partition.

Modern computers (since 2011 I think) come with UEFI rather than the old BIOS. UEFI can work with a MBR, but it's intended to work with a GPT. This new partitioning scheme is much more powerful, allowing for up to 128 primary partitions. There's still a MBR in the first sector of the disk, the Protective MBR, in case you want to use this disk with a BIOS based computer. After that you have the GPT lied over the next disk sectors (and with a backup copy right at the end of the disk), like this:

UEFI systems use an EFI System Partition that is normally the first disk partition and contains:

An ESP contains the boot loaders or kernel images for all installed operating systems (which are contained in other partitions), device driver files for hardware devices present in a computer and used by the firmware at boot time, system utility programs that are intended to be run before an operating system is booted, and data files such as error logs.

Usually USB drives and external disks come with a MBR partitioning scheme, but if you intend use it as a bootable USB device with multiple partitions you could find useful to change it to use a GPT scheme.