Have you ever wondered how a computer boots up? Regardless of hardware or operating system, all computers start up using either the traditional BIOS-MBR or the more recent UEFI-GPT method employed by the latest versions of Operating Systems available.
In this article, we will compare GPT and MBR partition structures; GPT stands for GUID Partition Table, while MBR stands for Master Boot Record. First, we start by understanding the boot process.
The following chapters highlight differences between GPT and MBR partition styles, include instructions on how to convert between the two styles, and offer advice on what to choose.
When you hit the power button of your PC, an execution begins that will eventually load the Operating System into memory. This first execution depends on the partition structure of your hard disk.
We have two types of partition structures: MBR and GPT. The partition structure on a drive defines three things:
Back to our boot process. So if your system is using the MBR partition structure, the first execution process will load the BIOS. Now, BIOS - Basic Input/Output System comprises the bootloader firmware. The bootloader firmware contains low-level functions such as reading from the keyboard, accessing video display, performing disk I/O and the code to load a first stage bootloader. Before the BIOS can detect the boot device, it goes through a sequence of system configuration functions starting with:
Once BIOS has detected the boot device, it reads the first disk block of that device into memory. The first disk block is the MBR, and it has a size of 512 bytes. It contains three items that have to fit into this space:
At this stage, the MBR scans the partition table and loads the Volume Boot Record (VBR) into RAM.
The VBR usually contains an Initial Program Loader (IPL) which is the code that initiates the boot process. The Initial Program Loader comprises the second stage bootloader which then loads the operating. On Windows-NT derived systems such as Windows XP, the IPL first loads another program called NT Loader (abbreviated as NTLDR) which then loads the operating system.
For Linux based Operating Systems, a bootloader called GRUB is used. The boot process is just similar to the one described above, the only difference being at the naming of stage 1 and stage 2 bootloaders.
Under GRUB, the stage one bootloader is called GRUB stage 1. GRUB Stage 1 loads second stage bootloader known as GRUB Stage 2. The second stage bootloader loads operating systems on the hard drive and presents the user with the list of operating systems to boot.
Still on the boot process; with a GPT partition structure, the following happens. GPT uses UEFI which avoids the MBR process of storing stage one bootloader which then loads stage 2 bootloader. UEFI - Unified Extensible Firmware Interface is more advanced than BIOS and can parse a file system and even load files on its own.
So, on powering on your computer, UEFI first performs the system configuration functions such as power management, setting dates and other system management components just as in BIOS.
UEFI then reads the GPT - GUID Partition Table. GUID stands for Globally Unique IDentifier. GPT is located on a drive's first blocks, just after block 0 which still holds MBR for Legacy BIOS.
GPT defines the partition table on a disk from which the EFI bootloader identifies the EFI system partition. The system partition contains bootloaders for all Operating Systems installed on other partitions on the hard drive. A bootloader initializes a windows boot manager which then loads the Operating System.
For Linux based Operating Systems, there’s an EFI aware version of GRUB (Grand Unified Bootloader) that loads a file such as grub.efi or the EFI loader that loads a file such as elilo.efi.
You may have noticed that both UEFI-GPT and BIOS-MBR loads a bootloader without loading the operating system directly. However, in UEFI, there's no going through multiple bootloaders as seen in BIOS. The boot process happens very first depending on your hardware capabilities.
If you have ever tried installing a Windows 8 or 10 operating system on a new computer, chances are you have been asked whether you want to use MBR or GPT partition structure.
If you are interested in knowing more or are planning to setup your computer with a new operating system, then keep on reading. We have already looked at the differences in the boot processes which you should keep in mind when partitioning a drive or deciding a partition structure.
GPT is a newer and more advanced partitioning structure, and comes with many advantages as I will list below. MBR has been in use for a long time, it’s stable and still the most compatible. Although GPT may be gradually replacing MBR because GPT has more advanced features, MBR is still necessary in some cases.
MBR is the traditional partitioning structure for managing a drive's partition. Since it is compatible with most systems, it still being used widely by most people. The MBR resides at the very first block of a hard drive, or in simpler terms, at the beginning of a hard drive. It holds the partition table - the information on the organization of logical partitions in the hard drive.
The MBR also contains executable code that scans through the partitions for an active OS and initializes the bootup procedure for the OS.
An MBR disk only allows four primary partitions. IF you would like more partitions, you can set the fourth partition as an extended partition, and it will let you create more sub-partitions or logical drives within it.
MBR uses 32-bit to record the partition, so each partition is restricted to a maximum of 2TB in size.
GPT is the newer standard for defining the partition structure of a hard disk. It uses GUID (Globally Unique Identifiers) to define the partition structure.
It is part of the UEFI standard, meaning a UEFI based system can only install on drive that uses GPT, for example, Windows 8 Secure Boot feature.
GPT allows for the creation of unlimited partitions even though some Operating Systems may restrict to 128 partitions. Also, GPT does not have a limit on the size of a partition.
The first block (block 0) of a GPT drive contains a protective MBR which has information showing the drive has a single partition extending across the entire drive. In case you use an old tool that can only read MBR disks, it will identify one partition extending across the entire hard drive. By doing so, it ensures the old tool won't mistake the GPT drive for being empty and end up overwriting its GPT data with a new MBR.
This MBR protects the GPT data from being overwritten.
Intel Mac Books use GPT by default, and it's not possible to install Mac OS X on an MBR system. Even though Mac OS X might run on MBR disk, installing on it is what is not possible. I have literally tried this without success.
Most Linux Operating Systems are compatible with GPT. On setting up a Linux OS on a disk, GRUB 2 will be installed as the bootloader.
For Windows Operating Systems, booting from GPT is only possible on UEFI-based computers running 64-bit versions of Windows Vista, 7, 8, 10 and corresponding server versions. If you purchased a laptop that came preinstalled with Windows 8 64-bit version, chances are it's using GPT.
The default configuration for Windows 7 and earlier versions is MBR, but you can still convert to GPT as I will explain in this article.
All versions of Windows Vista, 7, 8, 10 can read and use GPT for data - but they can't boot from GPT drives without UEFI.
You can be comfortable with either MBR or GPT. But given the advantages, GPT has over MBR as listed earlier, and the fact that modern computers are migrating towards it, you may probably consider using GPT. If your goal is to support older systems or want to boot a computer that uses the traditional BIOS, then you will have to stick to MBR.
Check the Partition Type of a hard drive
You can check the partition type of any hard drive connected to a Windows PC using Disk Management. To start Disk Management, do the following:
Use the keyboard shortcut Windows-R to open the run box.
Type diskmgmt.msc, and hit the Enter-key.
Windows scans the hard drives, and displays a representation after a short moment. To check the partition type of any hard drive, start by right-clicking on the Disk tiles in the lower half of the interface. It is important that you right-click on Disk 1, Disk 2 and so on, and not on the partitions.
Select the properties option from the context menu that opens. This opens the properties window of the selected disk.
Switch to the Volumes tab, and look at the Partition style value under disk information on the page that opens. It highlights the partition type.
If you prefer to use the command line, you may do the following instead. The advantage of the method is that it is a bit faster, as it lists all disks and the partition style directly.
All disks are listed now. Check the Gpt column to find out whether a particular disk is MBR or GPT. If you see a * in the column, it means that a disk is using GPT, if you don’t, it uses MBR.
There are two common error messages you are likely to get when installing windows on a hard drive:
When either of these error messages shows up, you may not be able to choose a partition to proceed with the installation. But this does not mean your computer has a problem.
As you already know, MBR and GPT are two entirely different partition structures of a hard disk. MBR being the traditional partitioning structure and GPT being the newer standard.
Error #1 shows up when you try to install Windows on a UEFI-based PC yet the hard drive partition is not configured for UEFI mode or legacy BIOS-compatibility. There are two options from Microsoft TechNet to help you get around this error.
Of course there are third-party utility software to help convert the disk to GPT format and still preserve the data, but it’s always safe to backup the data just in case the utility fails to complete the conversion
Using Windows Setup
Instructions for converting a hard drive from GPT to MBR
Sometimes it may be necessary to convert to MBR partition structure, for instance when you see the error message below while trying to install windows to disk.
"Windows cannot be installed to this disk. The selected disk is of the GPT partition style."
Booting from GPT is only supported on 64-bit versions of Windows Vista, 7, 8, 10 and corresponding server versions on UEFI-based systems. The above error message shows that your computer does not support UEFI and hence you can only use BIOS which works with MBR partition structure.
To go around this error message, Microsoft TechNet suggests the following options:
If you choose option two of converting to MBR follow these steps:
Using Windows Setup
Using manual conversion
What are Drive Partitions?
Differences between BIOS and UEFI
MBR and GPT Partition Tables
The following resources offer further reading on MBR or GPT partition styles:
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