UEFI+GPT Guide Basics (i): What is GPT and what is UEFI?

In fact, a few articles on Uefi wrote very early, just read it once and feel very dissatisfied, decided to rewrite. The goal is to write the content in the simplest and most straightforward language so that everyone can read it easily. Of course, if you have a deep understanding of the content, this article in addition to wasting your time is probably no good, it is recommended to go to the UEFI official website to download the UEFI specification document, where detailed description of UEFI, GPT each technical details.

In fact, UEFI, GPT is not a new thing, but because the pre-installed WIN8 computer designated to adopt this standard so as if in a night about UEFI started windows of the article has sprung up, many people are probably also the first to hear that this thing in the world. Since UEFI and GPT are "new" technologies, there must be more advanced and NB-BIOS+MBR of older technologies. Where the hell is NB? Here's a quick comparison:

GPT and its advantages

GPT and MBR are two different partitioning schemes. Currently the disk partitioning scheme widely adopted under Windows is still the MBR partition structure, but it is not suspected that GPT is the future trend. We can simply represent the MBR disk partition structure (basic disk under Windows, 4 primary partitions):

MBR partition structure

To make it easier for the computer to access the hard disk, divide the space on the hard disk into chunks (called sectors, or sector), and then assign an address to each chunk, called the Logical block address (that is, LBA).

The boot code and hard disk partition table are saved in the first sector of the MBR disk. The purpose of the boot code is to instruct the computer to boot the operating system from the active partition (the way the operating system starts under the BIOS), and the partition table to record the partition information of the hard disk. In the MBR, the size of the partitioned table is fixed and can hold 4 primary partition information altogether. In the MBR partition table, the logical block address is represented by a 32-bit binary number, thus representing a total of 2^32 (2 of the 32-square) logical block address. If a sector size is 512 bytes, the maximum partition capacity of the hard disk is only 2TB.

The GPT disk partition structure can be easily represented (basic disks under Windows):

GPT partition structure

As you can see, in the first data block of the GTP disk there is also a tag similar to the MBR (Master boot record), called PMBR. The PMBR function is that when using a partition tool that does not support GPT, the entire hard disk will be displayed as a protected partition to prevent partition tables and hard disk data from being compromised. UEFI does not get partition information for GPT disks from PMBR, it has its own partition table, or GPT partition table.

GPT's partitioning scheme is more advanced than MBR because the maximum number of partitions can be customized in the GPT partition header, which means that the size of the GPT partition table is not fixed. In Windows, Microsoft sets the maximum number of GPT disk partitions to 128. In addition, the logical block address (LBA) in the GPT partitioning scheme is represented by a 64-bit binary number, which can be used to calculate how large the 2^64 is, and it is perfectly reasonable to assume that the size is approximately equal to infinity in our demand. In addition, the GPT partitioning scheme has a backup partition table at the end of the hard disk, ensuring that the partition information is not easily lost.

Support for GPT disks by the Windows operating system

Because the BIOS does not recognize GPT partitions, GPT disks under the BIOS cannot be used to boot the operating system and can be used for data storage if the operating system provides support.

UEFI can recognize both MBR and GPT partitions, so both MBR disks and GPT disks can be used to start the operating system and data storage under UEFI. However, Microsoft restricts the installation of the operating system using Windows Installer under Uefi to install the system on GPT disks only.

The following table lists the levels of support for GPT disks for each version of the Windows operating system:

32-bit Windows support for GPT partitioning

64-bit Windows support for GPT partitioning

UEFI and its benefits

UEFI is an upgrade alternative to the BIOS. On the comparison between BIOS and UEFI, there are already a lot of related articles on the network, which are not mentioned here, only from the system startup principle. UEFI is more powerful than the BIOS because UEFI itself is already the equivalent of a micro operating system, and its convenience is:

First, UEFI already has file system support, it can directly read the files in the FAT partition;

What is a file system? Simply put, the file system is the operating system organization and management of the file, a straightforward point is that the data on the hard disk as a file presented to the user. FAT32, NTFS are common file system types.

Second, you can develop applications that run directly under UEFI, which usually ends with EFI.

Since UEFI can directly identify files in a FAT partition, there are applications that can be run directly in it. Then you can completely make the Windows Installer into an EFI-type application, and then put it in any FAT partition to run directly , so that the installation of the Windows operating system that seemed a little bit complicated in the past suddenly became very simple, It's as simple as opening QQ under Windows. And in fact, that's the case.

You know, these are not what the BIOS can do. Because the system boot code (included in the master boot record) must be read from the specified sector on the hard disk before booting the operating system under the BIOS, boot the operating system from the active partition. The operation of the sector is far less straightforward than the operation of the files in the partition, so booting the Windows operating system under the BIOS, we have to use some tools to configure the device to meet the boot requirements. In the UEFI, none of these need, no longer need the master boot record, no longer need the active partition, no tools, just copy the installation file to a FAT32 (primary) partition/U disk, and then boot from the partition/U disk, install Windows is so simple . There will be a special article in the following to detail the method of installing Windows7, 8 in Uefi.

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The article hastily changed, if there is a mistake to point out.

UEFI+GPT Guide Basics (i): What is GPT and what is UEFI?