Relationship between primary partitions and logical partitions in linux

Relationship between primary partitions and logical partitions in linux
The difference between a primary partition and an extended partition is that the primary partition is located at the beginning of the hard disk, where the MBR sector is located. The data at this position is automatically read and executed by the BIOS when the computer is started, that is to say, the partition table at this location will be automatically read to the memory by the BIOS, so that the MBR startup program can directly obtain the information of the primary partition table without any operation. However, because the MBR only has 512 bytes, the partition table also occupies 4x16 bytes, and there is a 55AA sign that occupies 2 bytes, the actual MBR can hold the executable program code space of only 446 bytes. The size of the 446-byte restricted program is too small to implement some functions. Therefore, the system needs to use some system operations provided by the BIOS for simple startup, the simple cost is that the 446-byte program cannot directly read the data in the logical partition in the extended partition and start the system, because the logical Partition Table of the extended partition is at the back of the hard disk, that is, in the data zone, the location is not fixed and needs to be searched multiple times to find the corresponding partition location. The 446-byte program cannot be operated at all.
In addition, because the system has not yet been fully accessible, the BIOS provides many features, but it is still not required to perform some special operations.

This is why Windows, even if you install extended partitions, puts a lot of things on the C drive. Because Windows requires that the C drive must be a primary partition to start the system.
Linux GRUB can be installed in extended partitions because after using the MBR's 446 bytes, several idle sectors after the MBR will have about 8 KB of capacity to continue with the program, this design reduces the volume limit. In this way, he can continue to call the program code at a specific location on the hard disk to continue the boot, not necessarily the primary partition.

To sum up, the main difference between the primary partition and the extended partition is the problem of starting the system. The old hardware design of BIOS has killed many programmer brain cells.