What is meant by physical address, an ancient method of addressing magnetic heads

Physical address is the disk's cylinder address, head address, and sector address, by which the location of data storage is determined.

CHS (Cylinder/Head/Sector) addressing mode, also known as 3D mode, is the earliest addressing mode used in hard disks, which was created on the premise that hard disks had a small capacity.

The C/H/S 3D parameters of a hard disk allow both the capacity of the disk to be calculated and the exact location of where the data is located. This is because the 3D physical address of a sector corresponds one-to-one with the physical sector on the hard disk, i.e., the 3D physical address completely identifies the physical sector on the hard disk. Three-dimensional physical address is usually written in the order of C / H / S, such as C / H / S for 0 / 1 / 1, then the first number 0 refers to the 0 column surface, the second number 1 refers to the 1 head (disk), the third number 1 refers to the 1 sector, indicating that the data is located in the hard disk 1 disk surface on the 0 track 1 sector. Now that the positioning is complete, an agreement is made between the internal parameters of the hard disk and the motherboard BIOS to correctly signal addressing and thus correctly locate the data position.