Want to install Windows XP but keep Vista already installed? Then read this article. The process of installing two systems can be a little confusing and time-consuming, but by doing so, you can work on two operating systems (separately).
Steps

Step 1. Back up important data
Although the data will not be affected when installing the second system, this step can save you from losing data in the event of unexpected errors.

Step 2. Take the installation disc for the system you want to install as the second system
Also prepare the installers of the programs that you want to install on the new operating system.

Step 3. If the already installed system occupies the entire disk, then you need to split it into partitions in order to be able to install another operating system
(It is best to install the second system on a separate hard drive, but a separate partition will work as well.) Check the system requirements for the operating system you want to install to create a partition of the appropriate size. You can also create a third section for storing data (this section will be available to both systems). Note that different operating systems will require partitions with different file systems.

Step 4. Install the operating system on the first partition (select the partition during installation)
If you already have one operating system installed, skip this step.

Step 5. Install the second operating system on the second partition
The installer for the second operating system will detect the first system and configure the boot loader correctly.

Step 6. If necessary, configure the boot loader using NT Loader (Windows) or GRUB (Linux)
Read on for information on how to do this. You must specify the operating system that will be loaded first (by default) and set a time delay during which you can select another operating system (after this time, the system selected by the system by default will be loaded).

Step 7. Test the correct system installation and bootloader configuration
To do this, boot each system, identify and troubleshoot (if any).

Step 8. Install the required programs
If you did not reinstall the system on the first partition, then the installed programs will work. But on the second system you need to install programs.
Advice
- It is better to perform the described actions on a new computer, since there are still few data / programs on it that need to be backed up or reinstalled. But some newer computers are missing the required drivers, so find and install them first.
- When installing two Windows systems, please install the old system first.
- Some operating systems can be installed on one partition, others cannot. Either read the documentation or create a separate partition for each operating system right away.
Warnings
- Back up your files.
- Before installing a second system, think again if you need it. During the installation process, unexpected glitches / errors / other may occur, which may affect the already installed system.