What does MBR stand for?
MBR stands for Master Boot Record. The legacy partition scheme and boot sector at the start of a disk. It is limited to 2 TB disks and four primary partitions (or three plus an extended one), and it is what legacy BIOS boots from; GPT with UEFI replaces it.
The MBR is the first sector of a disk partitioned in the traditional way. It holds a small boot program and a table with room for four primary partitions. Because the table stores sector numbers in 32 bits, it cannot describe more than about 2 TB of a disk with standard 512-byte sectors. A PC in legacy BIOS mode starts by running the code in the MBR. The scheme has been replaced by GPT on current systems, but it is still found on older PCs and on small removable drives.
MBR in practice: an example
An old PC stops booting with the message that no operating system was found, after malware overwrote the first sector of the disk. The partitions and files are intact. The technician starts from recovery media and rewrites the boot record, and Windows starts again.
What MBR is confused with
MBR vs GPT: what is the difference?
MBR supports four primary partitions and about 2 TB, with one copy of the table. GPT supports far larger disks and many more partitions, and keeps a backup copy of the table. What GPT stands for
Which exams cover MBR?
MBR is on the official CompTIA acronym list for one of the four exams covered here.
- A+ 220-1201 and 220-1202: 220-1202 1.0 (Operating Systems).
Each number is a CompTIA exam objective and the name in brackets is its domain. The exam puts the term in a scenario; it does not ask you to recite the expansion.
Check yourself: two practice questions
Written by CertSprint for this page. They are not taken from any exam.
1. What is the largest disk size that an MBR partition table can fully use with 512-byte sectors?
- About 2 TB
- About 137 GB
- About 16 TB
- There is no limit
Show the answer
A. About 2 TB. The 32-bit sector numbers in the table reach about 2 TB. Anything beyond that is invisible on an MBR disk.
2. How many primary partitions can an MBR disk hold?
- Two
- Four
- Sixteen
- One hundred and twenty-eight
Show the answer
B. Four. The table has four entries. More volumes require turning one entry into an extended partition with logical drives inside it. 128 is the GPT figure on Windows.
Sources: Microsoft Learn: Windows and GPT FAQ; Microsoft Learn: Initialize new disks. The acronym and its expansion come from CompTIA's official acronym lists, linked from each exam glossary above. The explanation, example and questions are CertSprint's own, checked against these sources on 11 November 2026.