Hard disks are preformatted by the manufacturer in a physical structure. For compatibility with the BIOS and various operating systems, Cylinder, Head, Sector (CHS) is used as the basic logical structure. In the CHS process, the physical structure of hard disks is simulated. CHS divides these into cylinders, read/write heads (head) and sectors.
As far as the storage capacity of the CHS procedure was concerned, the maximum, manageable storage capacity in the standard version of CHS was 504 megabytes( MB). This value results from the sector size of 512 bytes, the number of sectors, which was 63, the 16 read/write heads and the 1,024 cylinders.
Since the limits of this memory size were quickly reached, the E-CHS method was developed. This hard disk addressing, introduced in 1993, was a type of mapping that no longer worked with the physical disk values, but with logical ones that were converted during mapping. With E-CHS (Enhanced) the number of addressable read/write heads in the ATA standard was expanded from 16 to 255 virtual ones. Since the number of addressable cylinders did not change with 1,024, nor did the number of sectors of 63 and the sector size of 512 bytes, E-CHS results in a manageable memory size of 8.422 gigabytes( GB).
This limitation is removed by Logical Block Addressing( LBA) or by a BIOS extension via interrupt 13, Int 13, especially since modern motherboards work with hard disk capacities in the three- digit gigabyte range.