When I erase my external hard drive in Disk Utility, I find Master Boot Record is listed in the scheme drop-down menu. What it is, should I choose Master Boot Record or the commonly used GUID Partition Map? I also see MBR when I format a hard drive on a Windows PC, so I wonder if MBR is widely used, right?
Master Boot Record, short for MBR, is a special type of boot sector located at the very beginning of a storage device, like a hard disk or USB drive. It is stored in the first sector of a storage device, specifically at sector 0, cylinder 0, and head 0, and is only 512 bytes in size.
MBR plays two critical roles, one is helping boot a Windows computer while the other is managing partitions on disks.
As the boot loader that helps boot the OS, MBR contains the initial code (boot loader) necessary to launch the boot of the system. When a Windows computer is powered on, the system’s BIOS (on legacy systems) or UEFI (on modern systems operating in BIOS compatibility mode) looks for MBR on the primary storage device. The boot loader code of MBR will then load the full operating system from a bootable partition on the disk. If the boot loader in the MBR is corrupt or missing, the computer won’t start the operating system.
As a partition scheme, MBR contains a partition table that defines how the disk is divided into partitions. This allows the disk can be partitioned into different sections for different uses and meanwhile guarantees the system to access different sections of the disk freely.
MBR supports up to four primary partitions on a hard disk, and one of these can be an extended partition containing multiple logical partitions.
MBR is not widely used now. MBR is more commonly used on older Windows versions, but newer versions typically use GPT (GUID Partition Map). In macOS, MBR is usually not chosen as the partition scheme. The first choice is the GUID Partition Map. macOS can read and write to MBR-formatted disks (like USB drives). I think that’s the reason why it is listed in the scheme menu in Disk Utility.
In terms of MBR vs GPT, although both the two partition schemes are used to define how data is organized on a storage device, they have different features.
Usage: MBR is older and more commonly associated with Windows legacy systems, GPT is the modern standard and offers many advantages in both Windows and macOS.
Storage Capacity: MBR supports disks up to 2 TB in size while GPT supports drives up to 9.4 ZB (zettabytes), a massive size far beyond current storage needs.
Partition numbers: MBR can only support four primary partitions. When more partitions are needed, one of the primary partitions can be an extended partition, within which multiple logical partitions can be created. GPT can allow up to 128 primary partitions.
OS compatibility: MBR is compatible with older operating systems like Windows XP, Windows 7 (32-bit), and earlier versions of Linux, but macOS can also support MBR. GPT is widely used on modern versions of Windows (such as Windows 10 and 11, on UEFI systems), macOS, and Linux.
Read more details about MBR vs. GPT.