Legacy How BIOS boot is started or booted

What is the difference between a Windows 8 64-bit operating system and a full UEFI boot start-up, as in the past legacy boot? Let's get to know each other today.

How the Legacy BIOS UEFI boot is started or booted

When the system is first booted, or when the system is reset, the processor executes a code at a known location. This position is in the basic input/output system (BIOS). The CPU calls this reset vector to start a program at a known address in the Flash/rom. Typically, it performs a start self Test (POST) to check the machine. Finally, it loads the first sector from the Master boot Record (MBR) on the boot drive.
The
Bootstrapper is located in the first sector of  MBR . At this point the bootstrapper is loaded into  RAM  and executed. This boot loader is smaller than  512  bytes (a sector) in size. After the bios  self-test is completed, the code of  MBR  is read into memory, and the management is given to  MBR , MBR  re-read  dpt  from  DPT   (disk partition table, the hard disk partition table occupies the  MBR  sector's 64 bytes (offset 01beh--offset 01FDH)) to find out which of the hard disk's partitions is the active primary partition. So far, so the system is the same. Here's the difference.  DPT after reading the primary partition and then finding the primary partition  PBR  (partition boot record  partition boot record), PBR is located in the first sector of the active primary partition. When installing different operating systems  PBR  is going to be changed, xp   PBR  write dead code is to find  NTLDR . The  PBR  of  Vista  and  7  is written to find  Bootmgr .

The Boot Manager interface is not displayed on the monitor at this time. After Bootmgr was found, management was handed over to Bootmgr. Boot Manager first reads the language version information of the Boot Manager menu from the BCD and then calls the BOOTMGR with the corresponding language's BOOTMGR. Exe. MUI makes up the boot menu for the appropriate language before the boot manager is displayed on the display, which is the text interface that selects multiple operating systems. Finally, when you choose the appropriate operating system, here is Win7 or 8 (if you choose XP, will go to the XP boot process, find XP Ntldr and then start), Bootmgr to find the system partition (System partition and primary partition concept is not the same OH) windows/syste M32 under Winload.exe loads the operating system kernel.

EFI Boot Introduction

EFI's full name is the Extensible Firmware Interface (extensible Firmware Interface), which is the recommended standard for Intel Corporation for new types of firmware architectures, interfaces, and services. The standard has two main uses: to provide a set of standard operating environment for the boot program of the operating system and some applications running when the computer is initialized, and to provide an interactive protocol for the operating system to communicate with the firmware.

Simply put, EFI is the replacement of the BIOS. It provides a more powerful, secure, and convenient way to interact with the operating system and firmware. The EFI specification defines the interfaces, including data tables that contain platform information, that can be used in OS Loader and OS startup and runtime services.

The EFI firmware provides several technical advantages:

1. 
   

   Boot capability supports large capacity disks (more than 2 TIB);

2. 
   

   Faster start-up;

3. 
   

   The architecture of the independent CPU;

4. 
   

   Independent drivers for the CPU;

5. 
   

   Flexible pre-operating system environment, including network functions;

6. 
   

   Modular design;

EFI boot also requires a special partition table that points to a special file. Typically the file is located in the EFI path, EFI boot involves a boot loader written to firmware, EFI does not place the launcher in the MBR, firmware knows how to read the partition table and the FAT file format. The EFI system partition is a specific partition formatted with the FAT format, which contains the boot loader, which is the EFI executable that can be loaded and run by the EFI Boot manager.

The

boot loader  is set to a file that can be accessed through the firmware. boot loader  allows the user to select and load the operating system. All  boot manager  contains a  EFI  variable that is used to define the firmware configuration parameters.

mbr  and   GPT

MBR: Master boot record (master boot record, abbreviation: MBR), Also called the Master boot sector, which is the first sector that must be read when the computer accesses the hard disk, the three-dimensional address on the hard disk is (cylinder, head, sector) = (0,0,1).

The main boot sector records information about the hard disk itself and the size and location of each partition of the hard disk, which is an important entry point for data information. If it is compromised, the basic data structure information on the hard disk will be lost, and it will be necessary to re-access the original data after a tedious and tentative reconstruction of the structure information. The information in the main boot sector is written through a partitioner, which is a low-level format product that has no relation to the operating system (the operating system is created on top of the advanced formatted hard disk partition and is associated with a certain file system).

for hard disks, the possible number of bytes for a sector is  128x2n  (n=0,1,2,3). In most cases, take  n=2, which is the size of a sector (sector) of  512  bytes.

mbr  Restrictions:

1. 
   

   Up to 4 primary partitions or 3 primary partitions + one extended partition in the MBR partition table: The structure of the master boot record is known to contain only a 64-byte hard disk partition table. Because each partition information requires 16 bytes, it is possible to identify up to 4 primary partitions (Primary partition) for hard disks with MBR-type partition structures.

2. 
   

   MBR partitioning scheme cannot support disks that exceed 2TB capacity. Because this scheme uses 4 bytes to store the total number of sectors of the partition, the maximum can represent 2 of the number of 32 sectors, calculated per sector 512 bytes, each partition maximum can not exceed 2TB. When the disk capacity exceeds 2TB, the starting position of the partition cannot be represented.

GPT: Globally unique identity partition table (GUID Partition table, abbreviation: GPT) is the partition structure of an entity hard disk. The GUID partition table (GPT) was introduced as part of the extensible Firmware Interface (EFI) program. GPT provides a more flexible disk partitioning mechanism compared to the older master boot record (MBR) partitioning scheme that is commonly used by PCs.

GPT uses a GUID partition table (GPT) disk partitioning system. GPT disks provide the following benefits:

1. 
   

   allow up to  128  partitions, master boot record   (MBR)   disk can support  4   124  additional partitions within a primary and extended partition.

2. 
   

3. 
   

   because partitioned tables provide replication and cyclic redundancy   (CRC)   protection, they are more reliable.

4. 
   

5. 
   

Note: Windows supports only GPT disk booting from a system that contains Unified extensible Firmware Interface (UEFI) boot firmware.

The difference between GOP and VBIOS

VBIOS is a computer graphics card or integrated graphics controller bios, similar to the system BIOS provides a set of software used by the program functions to access the system hardware, VBIOS also provides a set of video-related programs used by the function to access video hardware. Typically a binary Bin file is provided by the graphics card manufacturer to the ODM manufacturer, which is wrapped in the system BIOS.

The GOP (Graphic output Protocol) driver is an EFI driver that replaces the traditional VBIOS black box in the EFI architecture and is designed to support the graphical output of basic requirements prior to operating system startup.

Vbt:video BIOS table. VBT is a specially crafted custom-made binary data block. By BMP utility to edit. VBT also like the legacy Vbios record the detail timing, GPIO Pins, Clock and other display parameters information.

The difference between the two: pre-OS boot period, EFI is the standard GOP protocol to achieve display output. The lagacy Vbios needs to be achieved through INT10 interrupter.

Which systems support UEFI boot? Why can't we support 32bit win8 UEFI boot at this moment?

The build of our BIOS is currently in x64 mode, so the 32-bit WIN8 UEFI is not supported.

Legacy How BIOS boot is started or booted