Whenever we install a new operating system, we see many options to tweak, and partition schemes are one of the important but confusing ones. When you are creating a bootable media, you see this option and choose the GPT or MBR partition scheme, and it decides where the operating system installs, and whether the system works or not. Normally, when you install Windows or other operating systems, the official tools like the Windows Installation media do everything for you, including the selection of the right partition table, depending on the firmware type (BIOS/UEFI) and the drive (SSD/HDD).
However, in manual installation, for example, when you are creating a bootable drive through Rufus, you’ll have to actively select the partition scheme; choosing it wrong can result in the firmware not detecting the OS drive at all. This is one practical example, but understanding MBR and GPT can help PC builders, system admins, IT professionals, and other power users can help them in various ways. So, let’s get started with a simple interactive tool.
What is a Partition Scheme and its purpose?
Imagine a partition scheme like a small blueprint that tells the computer (its firmware, mainly) how the storage drive is divided into sections or partitions. Some people imagine a partition scheme as a code, but it is most like a low-level binary data structure written in a specific format in the initial or end part of the disk (sector 0 for MBR, sector 1 for GPT). A partition scheme is a structure of data, or we can call it a defined layout of bytes. Some sectors are reserved on the storage device for it. Another good analogy for a partition scheme is a table of contents for the disk.
The partition scheme is formatted in a specific way (e.g., 64 bytes per MBR partition entry, 128 bytes per GPT entry).
Telling the system about the partition scheme is important for the first boot or installation because it defines where the bootloader is and how it’s read. See, when you boot your system, the firmware needs to find the code that starts to operating system. It is called the bootloader. In MBR, the bootloader is often in the same sector or sector 0. In GPT, the partition table points to the EFI System partition where the UEFI bootloader is stored.
In simple words, without the partition scheme, the system wouldn’t know what to do with your drive.
People are generally confused about the compatibility part of the MBR and GPT partition schemes, and less about their features (which we will cover later on). This happens mostly when they are using the modern storage drives on older systems or vice versa.
So, MBR is mainly for systems using the BIOS-only firmware. BIOS-only motherboards are rare to see these days. They were used back in the old days, and MBR was there to cater to the needs of that time. GPT is mainly for systems using the UEFI firmware. Now, most laptops or motherboards using the BIOS firmware have the option to select between Legacy and UEFI mode when you change the BIOS settings. So, with the UEFI mode, your system can use the GPT drive as its boot drive.
In GPT systems, you get CSM mode, which will allow you to use MBR as the primary OS drive. However, these modes should be selected carefully, and we will discuss that later on.
What is MBR (Master Boot Record)?
MBR or Master Boot Record was released in the early 1980s. At that time, very tiny operating systems were installed on very small drives. We are talking about the 10 MB hard drives. At that time, MBR was perfect because it catered to those needs. It is still used till now, so we can imagine its reliability in the computer world.
In MBR, the first sector of the drive (512 bytes) contains a tiny bit of code called the bootloader. It also has a partition table that can hold the partition information about only 4 partitions. If you want to create more than 4 partitions, a shady trick is used called the extender partition. It is basically a way to nest more logical partitions inside a single physical partition.
Besides the compatibility, the MBR was limited to working with drives with a maximum of 2TB storage space. So, if you are on MBR and using a 4TB hard drive, the system will recognize only 2TB of it. There are issues of corruption, and once the drive becomes corrupted, the whole drive becomes unreadable.
MBR was made solely for the BIOS firmware and was perfect for it at that time. But, as the system started to improve in terms of specifications and performance, the need for advanced firmware and then the partition scheme emerged. Then, we get the GPT partition scheme.
What is GPT (GUID Partition Table)?
GPT came into the presence in around 2005. It came along with the UEFI (Unified Extensible Firmware Interface), which replaced the old BIOS system. The main purpose was to serve the large file size and offer better support and performance for the UEFI firmware. With the GPT, we can have 128 partitions on a drive without any hacks. Theoretically, we can use a drive of the maximum size of 9.4 Zettabytes. To protect the drive from corruption, GPT keeps redundant copies of the partition table at the beginning and end of the disk. Also, instead of using just the numbers for partitions like the MBR, GPT uses GUIDs (Globally Unique Identifiers).
GPT partition systems work with modern UEFI systems and have backup partition tables for recovery. It also includes error-checking with CRC32. Also, it is essential for modern OS features (like Secure Boot, Windows 11). All in all, GPT is the modern partition scheme that eliminates all the drawbacks that we had with MBR. At the same time, it comes with numerous advantages for security, scalability, performance, and compatibility.
BIOS vs UEFI Firmware and Their Relationship to MBR/GPT
If we talk about compatibility, both legacy and modern motherboards support both types of partitions. Most older motherboards, which are based on BIOS, have the option to select between legacy (for MBR) and UEFI (for GPT). However, motherboards with older chipsets, like Intel 41 and older, came with a BIOS with MBR-only partition schemes. So, if your system is really old, you should stick to MBR. But, after the launch of Intel’s 1st generation (Intel 55 chipset and after), the firmware was updated to UEFI with options to go with MBR as well, generally called CSM or Compatibility Support Module.
Limitations of MBR and Why GPT Was Created
There are many problems with the MBR partition scheme if we look at today’s computers and computational needs. The biggest one is the total allowed capacity.
MBR uses 32-bit addressing to define where partitions start and end. That limits it to addressing up to 2^32 sectors, where each sector is usually 512 bytes. That equals 2.2 TB max usable space. Only 4 partitions are the issue that we have discussed. Also, no redundancy and error-checking is there in MBR. Features like secure boot can’t be used even though the UEFI can boot from an MBR drive through CSM.
How to check your drive’s Partition scheme?
In Windows, it is really easy to do with the help of the Disk Management menu.
- Press Windows+X and select the Disk Management option.
- Right-click the drive name and click Properties.
- In the properties menu, choose the Volumes tab and look at the partition style. It’ll have GUID or MBR written over there.
- In macOS, you can go to Disk Utility and click the Partition tab.
- Check the partition style
- In Linux, you can run this command in the terminal and look for the sda type.
lsblk -o NAME,PTTYPE
Conclusion
MBR was pretty successful and useful in the earlier days when storage drives were smaller and systems were based on BIOS firmware only. GPT is the modern partition style, overcoming most of the limitations of MBR. The good thing is that most modern BIOS-only systems would support GPT drives through some tweaks in the BIOS settings. The same goes for the UEFI-based systems with the CSM or Legacy modes.