Manjaro Some basics of MBR v/s GPT and BIOS v/s UEFI

Some basics of MBR v/s GPT and BIOS v/s UEFI

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MBR

A master boot record (MBR) is a special type of boot sector at the very beginning of partitioned computer mass storage devices like fixed disks or removable drives intended for use with IBM PC-compatible systems and beyond. The concept of MBRs was publicly introduced in 1983 with PC DOS 2.0.

The MBR holds the information on how the logical partitions, containing file systems, are organized on that medium. Besides that, the MBR also contains executable code to function as a loader for the installed operating system—usually by passing control over to the loader's second stage, or in conjunction with each partition's volume boot record (VBR). This MBR code is usually referred to as a boot loader.

The organization of the partition table in the MBR limits the maximum addressable storage space of a disk to 2 TB (232 × 512 bytes). Therefore, the MBR-based partitioning scheme is in the process of being superseded by the GUID Partition Table (GPT) scheme in new computers. A GPT can coexist with an MBR in order to provide some limited form of a backwards compatibility for older systems.

From: http://en.wikipedia.org/wiki/Master_boot_record


GPT

GUID Partition Table (GPT) is a standard for the layout of the partition table on a physical hard disk, using globally unique identifiers (GUID). Although it forms a part of the Unified Extensible Firmware Interface (UEFI) standard (Unified EFI Forum proposed replacement for the PC BIOS), it is also used on some BIOS systems because of the limitations of master boot record (MBR) partition tables, which use 32 bits for storing logical block addresses (LBA) and size information.

MBR-based partition table schemes insert the partitioning information for (usually) four "primary" partitions in the master boot record (MBR) (which on a BIOS system is also the container for code that begins the process of booting the system). In a GPT, the first sector of the disk is reserved for a "protective MBR" such that booting a BIOS-based computer from a GPT disk is supported, but the boot loader and O/S must both be GPT-aware. Regardless of the sector size, the GPT header begins on the second logical block of the device.

From: http://en.wikipedia.org/wiki/GUID_Partition_Table


GPT uses modern logical block addressing (LBA) in place of the cylinder-head-sector (CHS) addressing used with MBR. Legacy MBR information is contained in LBA 0, the GPT header is in LBA 1, and the partition table itself follows. In 64-bit Windows operating systems, 16,384 bytes, or 32 sectors, are reserved for the GPT, leaving LBA 34 as the first usable sector on the disk.

From: http://www.diskinternals.com/glossary/guid_partition_table.html


GPT vs. MBR

Compared with MBR disk, A GPT disk can support larger than 2 TB volumes where MBR cannot. A GPT disk can be basic or dynamic, just like an MBR disk can be basic or dynamic. GPT disks also support up to 128 partitions rather than the 4 primary partitions limited to MBR. Also, GPT keeps a backup of the partition table at the end of the disk. Furthermore, GPT disk provides greater reliability due to replication and cyclical redundancy check (CRC) protection of the partition table.

From: http://www.partition-tool.com/resource/GPT-disk-partition-manager/partition-gpt-disk.htm

The GUID partition table (GPT) disk partitioning style supports volumes up to 18 exabytes in size and up to 128 partitions per disk, compared to the master boot record (MBR) disk partitioning style, which supports volumes up to 2 terabytes in size and up to 4 primary partitions per disk (or three primary partitions, one extended partition, and unlimited logical drives). Unlike MBR partitioned disks, data critical to platform operation is located in partitions instead of unpartitioned or hidden sectors. In addition, GPT partitioned disks have redundant primary and backup partition tables for improved partition data structure integrity.

From: http://www.diskinternals.com/glossary/guid_partition_table.html


BIOS

In IBM PC compatible computers, the Basic Input/Output System (BIOS), also known as System BIOS, ROM BIOS or PC BIOS, is a de facto standard defining a firmware interface. The name originated from the Basic Input/Output System used in the CP/M operating system in 1975. The BIOS software is built into the PC, and is the first software run by a PC when powered on.

The fundamental purposes of the BIOS are to initialize and test the system hardware components, and to load a bootloader or an operating system from a mass memory device. The BIOS additionally provides abstraction layer for the hardware, i.e. a consistent way for application programs and operating systems to interact with the keyboard, display, and other input/output devices. Variations in the system hardware are hidden by the BIOS from programs that use BIOS services instead of directly accessing the hardware. Modern operating systems ignore the abstraction layer provided by the BIOS and access the hardware components directly.

From: https://en.wikipedia.org/wiki/BIOS

UEFI

The Unified Extensible Firmware Interface (UEFI) (pronounced as an initialism U-E-F-I or like "unify" without the n) is a specification that defines a software interface between an operating system and platform firmware. UEFI is meant to replace the Basic Input/Output System (BIOS) firmware interface, present in all IBM PC-compatible personal computers. In practice, most UEFI images provide legacy support for BIOS services. UEFI can support remote diagnostics and repair of computers, even without another operating system.

The original EFI (Extensible Firmware Interface) specification was developed by Intel. Some of its practices and data formats mirror ones from Windows.] In 2005, UEFI deprecated EFI 1.10 (final release of EFI). The UEFI specification is managed by the Unified EFI Forum.

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