Overview of the boot process for computer operating systems

The operating system updates are fairly fast, from DOS to WIN32, 95, 98, ME, XP. Although the system has been constantly improving development, but in fact, each operating system has their own development space, but also have their own advantages and disadvantages. For example, WIN98 and win ME, their common feature is a good multimedia performance, support hardware and software, but the disadvantage is that the system is not stable, and such as Winnt, WIN2000 and other systems, there is a better stability and operability, but the system requirements are relatively high, not suitable for general primary use. At this time, many friends will have "fish and bear paws can not have both" sigh. So is it possible to install a variety of operating systems on one computer and choose any of them according to your needs? Of course, this is the multiple systems coexistence we are going to talk about.

To allow multiple systems to coexist, one must first understand some basic principles. In the above section, we talked about a bit, here to do a more in-depth analysis:

How does the operating system boot? When the system power-on self-test passes, the hard drive is reset and the BIOS starts from the floppy disk, the hard disk, or the optical drive according to the user-specified boot sequence. To boot from the hard disk, the system BIOS reads the master boot record into memory. You then give control to the primary bootstrapper, and then check the status of the partitioned table for the active partition. Finally, the master bootstrapper gives control to the active partition's boot record, and the boot record loads the operating system.

For operating systems such as DOS and Win9x, the partition boot record is responsible for reading and executing the Io.sys (windows9x io.sys).

First initialize some important system data, then there will be the blue sky and white clouds that we are very familiar with. At this point, Windows will continue to boot and initialize the DOS section and GUI (graphical user interface) section. If a system is installed with tool software that directs multiple operating systems, the master boot record will normally be replaced with the boot code for that software. The code will allow the user to select an operating system and then read and execute the operating system's basic code.

For winnt/2000, it is the NTLDR program that is responsible for loading it into memory or allowing the user to select a non-winnt/2000 operating system. Both the boot loader and the multiple boot are controlled by an initialization file with an implied attribute boot.ini. The boot.ini contains settings that control the operating system available to the computer, the boot default operating system, and how much time should wait for such information.

So, where are our chances? As the saying goes, good, jianfengchazhen. From the description of the computer boot process, we can find that there are only two places where we could artificially add one intervention, one is to set the boot order of the physical disk and the other is to modify the partition table of the Master bootstrapper.

(1) Multi-system coexistence of multiple hard disks: If you are using a computer with multiple hard disks, and each hard drive is equipped with different operating systems, it is recommended that you specify the boot sequence of the hard drive in the CMOS to achieve coexistence of multiple operating systems. This approach is completely unaffected by other factors, such as compatibility, because the operating system does not affect each other.

(2) Single Hard drive system coexistence: And if you only have one hard drive and want to install multiple operating systems on top of each other, you must modify the master bootstrapper and partition table to achieve this. There are generally two methods. One is to modify the master boot record, the master boot record at the end of the jmp instruction to jump to their own code to control the computer's boot process; Another approach is to modify the boot code for the first sector of the primary partition to achieve multiple system coexistence.

Note: Next, we will teach you how to do multiple system coexistence settings. Before you speak, however, there are some basic principles to tell you:

1. Before you install another operating system on your computer, it is a good idea to make a startup disk for unexpected purposes.

2. Each operating system must be installed on a separate disk drive or partition.

3. If you are going to have multiple boot configurations between DOS, WIN95 and Win 2000, you should finally install Win 2000. Otherwise, some of the important files needed to start WIN 2000 may be overwritten. For dual-boot configurations between win 98 and 2000, the installation of the operating system does not have to be in a specific order, and for the dual-boot configuration between Win 2000 and Linux, Win 2000 should be installed and the disk partitions required for Linux to be retained.

4. To perform a dual-boot configuration, you should use the FAT file system. Although NTFS is supported in dual booting, this increases the complexity of the file system.

5. Do not install Win 2000 on a compressed disk unless the compression disk is completed by Win 2000, and if you plan to establish a dual-boot of Win 95 or win 98, you do not need to decompress the compressed disk.

6. On a dual-boot computer, if you want your application to run on both operating systems, you must install on both operating systems, and you cannot share applications between operating systems.