Let’s talk about partition.
There are two types of partitions on a hard disk: primary and extended. Some are called secondary partitions. If you have only one primary partition on a hard disk, you can have a maximum of four partitions. This is because an extended partition can have as many as 24 logical drives that can be subdivided. Up to 24 logical drives can be specified, without AB (AB is the letter for floppy drive). When Windows is loaded, it boots to the primary active partition. You may be wondering if you can keep it.
Yes, there is only 64 KB in the boot partition table for boot information to install the OS on a hard disk. A boot partition table contains 16 KB.
For four operating systems, 16 * 4L 64, so only a maximum of four operating systems can be installed. So you can only partition the primary partition up to four… ok, so you can use it after installing Windows on a hard disk, but it will not work if the first boot device is not declared in the bios setting.