GPR VS MBR

Hard Disk Style


In general, MBR and GPT are two types of disk styles. As you know, before you first use a new hard drive, Windows will prompt a message saying "You must initialize a disk before Logical Disk Manager can access it" to tell you to initialize this disk with Windows built-in Disk Management. If you plug an SSD, an external hard drive or other data storage device to your computer for the first time, you should choose to initialize this device to MBR (Master Boot Record) or GPT (GUID Partition Table).

initialize

Usually, the default setting of Windows is to initialize to MBR and most of you straightly click "OK" to perform this initialization without choosing GPT. Furthermore, after a period of time, you will find this partition style you have selected for your SSD or other storage devices is unable to meet some needs, and you have to change your disk to GPT.

MBR VS GPT

MBR Layout VS GPT Layout

MBR is the abbreviation of Master Boot Record which is an old standard to manage the partitions in a hard disk. And nowadays this disk style is extensively used by many of you. MBR refers to a specific boot sector at the very beginning of the hard disk and it holds some information on how the partitions are organized in a hard disk. Generally speaking, MBR is made up of three parts, including executable code called the Master Boot Code, the partition table for the disk and the disk signature. Moreover, the boot code can be used to scan the partition table for the active partition, find the starting sector of the active partition, load a copy of the boot sector from the active partition into memory and transfer control to the executable code in the boot sector. In one word, it can load up the OS boot code or procedure from the active partition. Here is a picture about the MBR disk layout:

MBR

GPT is short for  Partition Table which is another disk type and it is the latest standard for the layout of the partition table of a hard disk. What’s more, GPT uses globally unique identifiers (GUID) to define the partition. As a part of the UEFI standard, it is used to replace MBR which uses 32 bits to store logical block addresses (LBA) and size information on a traditional 512-byte disk sector. GPT adopts primary and backup partition structures which respectively locate at the beginning and the end of the disk to provide redundancy. Like traditional MBR, GPT also uses logical block address (LBA) rather than relative sectors to identify these structures. At the very beginning of GPT partition table, there is Protective MBR which is used to prevent disk tools not supporting GPT disks from identifying the disk by mistake and damaging the disk data. Here is a figure of GPT disk layout below:

GPT

The Difference between MBR and GPT


After learning so much information about GPT VS MBR for SSD in layout, now let’s make a comparison for them in detail. When comparing MBR disk and GPT disk, you can clearly get five evident differences. Just read on.

img1 Partition Number

MBR: From the structure of Master Boot Record, you can know it contains a 64-byte partition table which is made up of four partition table entries and each one needs 16 bytes. Therefore, for an MBR disk, you are allowed to create four primary partitions. In order to create more partitions, it is OK to change the fourth partition as an extended partition, and then many logical drives can be created. Here Microsoft supports the sub-partitions can be up to 128. In other words, MBR disk supports up to four primary partitions or three primary partitions plus extended partition with up to 128 logical drives.

GPT: For a GPT disk, the partition table header defines the usable blocks on the disk and the number & size of the partition entries that make up the partition table. EFI requires that the partition table should be a minimum of 16,384 bytes reserved, namely there are 128 partition entries and each is 128 bytes. In brief, you can create up to 128 primary partitions on a GPT disk.

img1 Disk Size

In addition to MBR VS GPT in partition number, there is an obvious difference in disk size. For a hard drive of which sector is 512 bytes, the partition table of MBR limits the maximum addressable storage space to 2TB. That is to say, MBR disk only supports up to 2TB in capacity. If your disk is larger than 2TB, you will find the rest disk space becomes "unallocated" in Disk Management.

mbr larger than 2tb

Unlike MBR, GUID Partition Table allocates 64 bits for logical block addresses, hence a maximum disk size of 264 sectors is a possibility. For a hard disk with 512-byte sector, it is equivalent to 9.44 ZB (1 ZB is 1 billion terabytes) or 8 ZiB. All in all, GPT disk supports up to 18EB in capacity.

img1 MBR VS GPT in Security

Besides, there is another difference in security between MBR and GPT. When observing the disk layout of MBR and GPT, you will find there is primary GUID partition table header at the beginning of the hard disk and backup GUID partition table header at the end of the disk. Importantly, it also contains a CRC32 checksum for itself and for the partition table. With the checksum, the firmware, bootloader or operating system on boot can verify whether there is something wrong with the partition table. Once errors are detected on primary GPT, it is allowed to recover the whole partition table from the backup GUID partition header.

This is an outstanding advantage of GPT, whereas MBR doesn’t have such a feature. Once the partition table is corrupted, MBR disk is unusable. In this aspect, GPT has higher security than MBR disk.

img1 OS Support

The above content mentioned MBR VS GUID Partition Table in three aspects, moreover, you also need to pay attention to the supported operating system and BIOS. Generally speaking, legacy BIOS only supports MBR, but UEFI supports MBR and GPT. When comparing MBR and GPT in OS support, you should know all operating systems can be installed on MBR disk, namely MBR supports all versions of all OSs. However, on the contrary, not all Windows systems supports GUID Partition Table.

The Disadvantages of MBR

Earlier, we told you that MBR Partition Structure is quite old. It also means that you can still find a big bunch of devices that are based on MBR. Well, the noticeable issues with MBR Partition Structure are as follows.
  1. There is a limit to the size of Hard Drives in MBR partition structure. You cannot use it in devices that have a bigger size than 2TB. That is, if you have a 4TB Hard Drive for your system, you cannot set that up using Master Boot Record.
  2. You can create only 4 Primary Partitions using MBR. There are times when you need a higher number of primary partitions in the device.
  3. In comparison, MBR Drives aren’t really reliable. Due to corruption and other issues, MBR might get overwritten, causing some other issues as well. It’s because MBR-based drives are storing all data in a single location.
These issues were enough compelling for Intel to create a new partition structure – and we have GPT. Now, we will check out the bright side with GPT-based drives.

The Advantages of GPT

Here are some of the reasons why you have to create the next partition in GPT.
  1. There is no particular limit to the size of Hard Drives you can set up with GPT Partition Structure. It’s good enough if you have a bigger size HDD in the computer. For instance, if you are setting up a rig for gaming, you’d surely need something more than 2TB.
  2. GPT supports up to 128 Primary Partitions. When compared to the 4 in MBR, this is something huge.
  3. When compared to MBR, GPT has better reliability and protection. There are a few reasons for this. First of all, boot data and partition data are stored in multiple places in GPT Partition structure. Even if something happens to one, there are methods for recovery.
  4. GPT-based Drives will perform Cyclic Redundancy Checks for the booting and partition data stored. If the main data is being corrupted, the drive will try to do the recovery by copying data from other locations. On the other hand, in MBR, you have to do that manually.

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