UK How MBR works
The master boot record (MBR) is the first 512-byte sector of a disk. It holds three things: up to 446 bytes of boot code, a 64-byte partition table with room for four entries, and a two-byte signature that marks the sector as valid. It arrived with PC DOS 2.0 in 1983 and was the standard on PCs for nearly 30 years.
On a legacy BIOS system, the firmware reads this sector and runs the boot code, which finds the active partition and loads the operating system from there. Each partition entry stores its start and size as 32-bit sector numbers, which is where the size limit comes from: 232 sectors of 512 bytes is about 2 TiB. More than four partitions needs a workaround, an extended partition that holds a chain of logical partitions.
How GPT works
The GUID partition table (GPT) was designed as part of Intel’s Extensible Firmware Interface and is now defined in the UEFI specification. It uses 64-bit sector numbers, so the size limit is no longer a practical concern, and gives every partition a globally unique identifier (GUID).
A GPT disk starts with a protective MBR, a dummy entry that covers the whole disk so that older tools do not mistake it for empty space. The GPT header follows in the next sector, then the partition entries. A second copy of the header and table sits at the end of the disk, and both carry CRC32 checksums, so damage to one copy can be detected and repaired from the other.
MBR vs GPT compared
The practical differences come down to size, partition count, resilience and how the computer boots.
| Feature | MBR | GPT |
|---|---|---|
| Introduced | 1983, with PC DOS 2.0 | Around 2000, as part of Intel’s EFI, now the UEFI specification |
| Maximum disk size | About 2 TiB with 512-byte sectors | About 8 ZiB with 512-byte sectors |
| Partitions | Four primary, or three plus an extended partition | 128 by default on Windows |
| Partition table copies | One, in the first sector | Two: a primary at the start and a backup at the end |
| Error checking | None | CRC32 checksums on the header and table |
| Partition identifiers | One-byte type code | Unique GUID for each partition and type |
| Boots with | Legacy BIOS (or UEFI in CSM mode) | UEFI (and legacy BIOS on Linux with a BIOS boot partition) |
Microsoft only boots Windows from GPT on UEFI systems, and from MBR on legacy BIOS systems. Since Windows 11 requires UEFI, its system disk is always GPT. Linux is more flexible and can boot from either, which is one reason older embedded Linux images still use MBR.
The boot path differs too. With MBR, the boot code lives in that first sector and is easy to overwrite, which is how many old boot-sector viruses spread. With GPT and UEFI, the bootloader is an ordinary file on a small EFI System Partition, so it can be backed up, replaced and checked by Secure Boot like any other signed file.
Which to use on industrial and embedded systems
For a new build, GPT is the default. Current Windows IoT Enterprise industrial PCs boot in UEFI mode, and industrial NVMe drives of 2 TB and above already sit at the edge of what MBR can address. There are still a few places where MBR is the right call:
-
//
Legacy BIOS boards. Older x86 boards, including some long-life PC/104 stackable embedded computers, boot only in legacy mode, so the system disk must be MBR.
-
//
Validated older images. A qualified Windows 7 or DOS image built on MBR may be cheaper to keep than to requalify, as long as the disk stays under 2 TiB.
-
//
Removable media for older devices. SD cards, CFast cards and USB drives that must be read by older equipment are often safest as MBR.
-
//
Data disks. A second drive used only for data can be either. Choose GPT for anything over 2 TiB.
Partition tables and power loss
The partition table is a few sectors on the disk, and a corrupted one can leave a system that will not boot even though the data is still there. GPT’s backup copy and checksums make that easier to recover, but they do not stop the damage happening.
The bigger risk on site is a power cut during a write. Industrial SSDs with power loss protection that finishes cached writes reduce it, as does a read-only or write-filtered system partition, which Windows IoT Enterprise supports through its Unified Write Filter.
Quick answers on MBR and GPT
MBR and GPT: common questions
Should I use MBR or GPT for an SSD?
GPT, on any current computer. UEFI systems boot from GPT, Windows 11 requires it for the system disk, and GPT has no 2 TiB limit. MBR only makes sense for a legacy BIOS system or an older operating system that cannot boot otherwise.
How do I check if a drive is MBR or GPT?
Look at the partition style. In Windows Disk Management, open the disk’s Properties and the Volumes tab, or run Get-Disk in PowerShell. On Linux, lsblk -o NAME,PTTYPE shows “gpt” or “dos” for MBR.
How do I convert MBR to GPT without losing data?
Use MBR2GPT on Windows. MBR2GPT.exe, included since Windows 10 version 1703, converts the system disk in place. Switch the firmware to UEFI mode afterwards. The diskpart convert command only works on an empty disk.
Can I convert GPT back to MBR?
Only by wiping the disk, in most cases. Windows has no in-place tool for that direction. Back up the data, delete the partitions, convert and restore.
Is GPT faster than MBR?
No. The partition style does not change read or write speed. GPT is chosen for capacity, reliability and UEFI boot, not performance.
We partition, image and test the drives in every industrial PC we supply as standard, using GPT and UEFI unless an older operating system needs legacy boot.