The Master Boot Record (MBR) is the information in the first sector of any hard disk or diskette that identifies how and where an operating system is located so that it can be boot (loaded) into the computer’s main storage or random access memory. The Master Boot Record is also sometimes called the “partition sector” or the “master partition table” because it includes a table that locates each partition that the hard disk has been formatted into. In addition to this table, the MBR also includes a program that reads the boot sector record of the partition containing the operating system to be booted into RAM. In turn, that record contains a program that loads the rest of the operating system into RAM.


The GUID Partition Table (GPT) is a standard for the layout of partition tables of a physical computer storage device, such as a hard disk drive or solid-state drive, using universally unique identifiers, which are also known as globally unique identifiers (GUIDs).


An overview of MBR and GPT partitions

Before a drive can be divided into individual partitions, it needs to be configured to use a specific partition scheme or table.

A partition table tells the operating system how the partitions and data on the drive are organized. For example, the screenshots above show the partition tables on the drive, and each individual partition is shown as a rectangular block.

There are two main types of partition tables: MBR and GPT.

MBR stands for Master Boot Record, and is a bit of reserved space at the beginning of the drive that contains the information about how the partitions are organized. The MBR also contains code to launch the operating system, and it’s sometimes called the Boot Loader.

GPT is an abbreviation of GUID Partition Table, and is a newer standard that’s slowly replacing MBR.

Unlike an MBR partition table, GPT stores the data about how all the partitions are organized and how to boot the OS throughout the drive. That way if one partition is erased or corrupted, it’s still possible to boot and recover some of the data.

If you bought your computer within the last five years or so, it’s very likely that it’s using GPT partition tables rather than the older MBR tables.

Differences between MBR vs GPT partitions

There are a number of differences between MBR and GPT partitions, but we’ll cover some of the main ones here.

First, the maximum capacity of MBR partition tables is only about 2 terabytes. You can use a drive that’s larger than 2 terabytes with MBR, but only the first 2 terabytes of the drive will be used. The rest of the storage on the drive will be wasted.

In contrast, GPT partition tables offer a maximum capacity of 9.7 zetabytes. 1 zetabyte is about 1 billion terabytes, so you’re unlikely to run out of space anytime soon.

Next, MBR partition tables can have a maximum of 4 separate partitions. However, one of those partitions can be configured to be an extended partition, which is a partition that can be split up into an 23 additional partitions. So the absolute maximum number of partitions an MBR partition table can have is 26 partitions.

GPT partition tables allow for up to 128 separate partitions, which is more than enough for most real world applications.

As MBR is older, it’s usually paired with older Legacy BIOS systems, while GPT is found on newer UEFI systems. This means that MBR partitions have better software and hardware compatibility, though GPT is starting to catch up.


 Convert MBR to GPT Using DiskPart

If you want to convert MBR to GPT without data loss via CMD, you need to back up your files in advance and then perform data restoring after the conversion. If there are lots of files on your disk, you are recommended to back up your data effectively using the free back up softwares on the internet. 

After backing up the files and delete all the partitions on the disk, you can now follow the steps below to convert your disk using CMD.

Step 1. Open Command Prompt and type in DiskPart and press “Enter”.

Step 2. Then type in list disk (Note down the number of the disk you which you want to convert to GPT).

Step 3. Then type in select disk X (the number of the disk).

Step 4. Finally, type in convert gpt. and thats all you can now exit diskpart.

Convert MBR to GPT Disk with Disk Management

Similar to using CMD, you also need to delete all partitions on your disk using Disk Management. Before you convert the disk from MBR to GPT or from GPT to MBR, you should back up your disk. If you want to recover a deleted partition, you can use a partition recovery software tool to get your lost data and partition back.

Step 1. Right-click on “This PC”, choose “Manage”, then head to “Disk Management”.

Step 2. Right-click the volumes on your target disk and choose “Delete Volume…”

Step 3. When your disk becomes empty (shows as unallocated space), right-click your disk and choose “Convert to GPT Disk”.

Convert MBR to GPT in Disk Management

Convert MBR to GPT without data loss using Gptgen

Convert MBR to GPT

You can convert MBR to GPT without losing data – using a command-line utility called gptgen.

Gptgen is a tool designed to non-destructively convert hard disks partitioned in the common, “MSDOS-style” MBR scheme (including extended partitions) to use a GUID partition table (GPT).

It’s a very extensive tool but a bit complicated to run. According to the tool’s ‘read me’ file, the syntax of the tool is “gptgen [-w] \\.\physicaldriveX”,

  • Here X is the drive number reported by the Disk Management console or the “list disk” command of the DISKPART utility.
  • The -w switch makes gptgen write the generated GUID partition tables to the disk – otherwise, the primary table will be written to a file named “primary.img“, and the secondary table to “secondary.img“, in the directory that the program was invoked from.
  • You can then use dd to write the tables to the disk.

Convert MBR to GPT without losing data using Partition Assistant

The last method is using a tool called AOMEI Partition assistant Lite Edition. It’s a free multifunction partition management software. This tool’s feature can help you convert a disk with data into GPT or MBR style without data loss.

NOTE: It appears that now the free version of Partition Assistant does not allow converting MBR to GPT.

To convert a disk to MBR/GPT disk:

  • Select the disk to convert;
  • Right-click the disk and select Convert to GPT/MBR Disk;
  • Confirm your operation, by clicking “OK” to continue;
  • Click Apply button on the toolbar to commit the changes.

Use MBR2GPT Disk Conversion Tool

To convert MBR to GPT using the built-in MBR2GPT.exe tool:

Boot into Advanced start up options screen > Troubleshoot > Advanced options > Command Prompt.

Execute the following command to validate that the drive meets the requirements:

mbr2gpt /validate

Execute the following command to convert the drive from MBR to GPT:

mbr2gpt /convert

Restart your computer.

Do note that MBR2GPT can only be used from the Windows Preinstallation Environment. To use it from your Desktop, you have to use /allowFullOS to override.

Read more about the new MBT2GPT Disk Conversion Tool in Windows 10. Using this built-in tool, you can safely and non-destructively convert a Windows 10 computer from legacy BIOS to UEFI disk partitioning.

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Author: refuge_2020

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