MBR vs GPT: What’s The Difference?

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When setting up your PC, you may be prompted to choose between MBR or GPT for installing your operating system.

MBR and GPT are two common partition styles used on Windows-based computers to organize data on storage devices like HDDs or SSDs. 

These styles determine how Windows accesses and manages data on the disk and are chosen during the disk initialization process. 

Each disk must have a partition style, and before selecting one, it’s essential to understand the basic differences between MBR and GPT.

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What is Partition?

A partition represents a virtual division within a hard disk drive (HDD) or solid-state drive (SSD), where each partition serves a distinct purpose and can have different sizes.

In Windows, a typical setup often includes a small recovery partition and a larger file system partition labeled as C:. The C: partition is the one people are most familiar with since it’s where programs are installed, and various files are stored.

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What is MBR?

MBR, short for Master Boot Record, is a legacy disk type that was originally introduced with IBM PC DOS 2.0 in 1983. It derives its name from the boot sector, located at the very beginning of a drive (the first sector), which is referred to as the MBR.

MBR Sector

MBR and GPT disks share a common first sector known as the MBR sector. This sector has a size of 512 bytes and contains essential components like the master boot code (446 bytes), the disk partition table (DPT, 64 bytes), and a boot signature (2 bytes) that signifies the end of the MBR sector. The data stored within this sector provides vital information about how the partitions are structured on the storage device. If this sector becomes corrupted, the disk becomes unusable until the MBR is rebuilt.

Partitions

To utilize a disk for data storage, it must be divided into sections known as partitions. 

On an MBR disk, partitions are divided into two categories: primary partitions and extended partitions. 

Primary partitions are used for installing the operating system and can be set as active to enable booting the computer from them. The remaining space on the disk, excluding the primary partitions, is referred to as an extended partition.

An extended partition differs from a primary partition in that it serves as a storage unit that can only host multiple logical drives or partitions. Unlike primary partitions, the extended partition itself does not have a drive letter or file system. Instead, it acts as a container for one or more logical partitions, each of which can have its own drive letter and file system. It holds these logical partitions, allowing you to efficiently manage data and allocate storage space.

On an MBR disk, the partition table has a total size of 64 bytes, and each partition’s information requires 16 bytes. This means you can create a maximum of four primary partitions. If you need more than four partitions on the disk, you can convert one primary partition into an extended partition. Inside the extended partition, you have the flexibility to create multiple logical drives or partitions to meet your storage needs.

One significant drawback of an MBR disk is its limited capacity, supporting a maximum size of approximately 2.2TB (terabytes). If you have a disk larger than this, using the MBR partition style restricts you to utilizing only up to 2.2TB of space on the disk.

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What is GPT?

GPT, or GUID Partition Table, is a newer partitioning standard compared to MBR. It was introduced as part of the UEFI (Unified Extensible Firmware Interface) initiative. Unlike the MBR partitioning scheme, GPT offers greater flexibility and improved compatibility with modern hardware.

GPT Sector

• Protective MBR: On a GPT disk, the first sector also contains an MBR sector, but it serves a different purpose compared to the MBR disk. This protective MBR on a GPT disk acts as a safeguard, preventing tools designed for MBR disks from mistakenly identifying and potentially overwriting GPT disks. It helps ensure that GPT disks are correctly recognized and protected from unintended modifications.

• Primary GPT Header: The second sector on a GPT disk contains the primary GUID partition table header. This header specifies the partition entries’ location and size, including the partition table and a cyclic redundancy check (CRC32) checksum. The CRC32 checksum is utilized to ensure the integrity of the GPT header. In the event of data corruption, the CRC will attempt to recover the data by using the backups stored at the end of the disk. This redundancy helps maintain the reliability and consistency of the GPT disk structure.

• Partition Entries: Between the third and thirty-fourth sectors of a GPT disk (32 sectors in total), you’ll find the partition entries. Unlike MBR disks, GPT disks allow theoretically unlimited partitions. However, the actual number of partitions you can create will be determined by the limitations of the operating system. For instance, on Windows, each partition entry requires 128 bytes, allowing a maximum of 128 partitions (32 * 512 / 128 = 128). This significant difference in partitioning capability sets GPT disks apart from MBR disks, providing greater flexibility and scalability for organizing data.

• Partitions: Unlike MBR disks, GPT disks have no extended or logical partitions. You can create as many primary partitions as needed since there are no restrictions on the number of primary partitions.

• Backup Partition Entries/Primary GPT Header: GPT disks automatically store backups of the primary GPT header and partition entries on the last sectors of the disk. This built-in backup feature enhances the safety and reliability of GPT disks, making data restoration possible if the GPT header or partition table becomes corrupted.

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Difference Between MBR and GPT

MBR has been around for a long time and is associated with Legacy BIOS systems, while GPT is a newer scheme typically used with UEFI systems. 

One significant difference lies in the supported boot modes: MBR only supports BIOS boot mode, whereas GPT supports UEFI boot mode.

With MBR, the maximum capacity of a disk is restricted to 2TB, and you can only have up to 4 primary partitions, or 3 primary partitions and 1 extended partition that can be further divided into logical partitions. On the other hand, GPT supports much larger capacities, and you can have many more partitions, allowing for more flexibility in organizing data.

Moreover, GPT disks offer better protection against data corruption due to a backup of the partition table stored at the end of the disk, whereas MBR lacks this feature.

While MBR has better compatibility with older systems and software, GPT is becoming more prevalent, especially in modern UEFI-based computers. It provides advantages such as faster boot times, improved graphics and mouse cursor support, and support for larger hard drives.

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What is BIOS?

I’ve mentioned BIOS a few times before. Although it falls slightly beyond the scope of this article, having a fundamental understanding of BIOS is crucial. 

BIOS, short for Basic Input/Output System, is fundamental software stored on a chip within a computer’s motherboard. It activates when you power on the computer and plays a crucial role in the initial startup process.

For a detailed guide on BIOS and its functions, refer to our article “What is BIOS in a Computer.”

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Considering a Switch: MBR to GPT Upgrade – Is it Worth It?

If you currently have an MBR partition table on your drive, you might wonder if it’s worth transitioning to the newer GPT standard. In most cases, the answer is probably NO; as the saying goes, “if it ain’t broke, don’t fix it.”

Upgrading from MBR to GPT involves some risks, and a misstep can damage the MBR sector, resulting in an unbootable drive. To recover, you’d need to repair the MBR using recovery tools or reinstall the OS entirely, which can be quite a hassle.

However, certain situations might warrant an upgrade. For instance, if you plan to use a drive larger than 2 terabytes or require more than 26 partitions, GPT becomes essential. But before proceeding, ensure your hardware supports GPT and UEFI BIOS.

If you’re determined to switch to GPT, prioritize backing up your drive and important data to minimize potential losses. With a backup in place, you can easily revert to MBR if needed, saving you from the inconvenience of reinstalling everything from scratch.

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FAQs about MBR and GPT