System BIOS and Hard Drive Related FAQs (Part I)

System BIOS The most commonly asked questions about the system BIOS and its relationship to hard drives. The following will provide you with basic information beginning with the definition of a BIOS, to identifying key features found in various BIOS’s. The purpose of this document is to aid you in solving minor difficulties you may be currently experiencing.

1. What is Logical Block Addressing (LBA)?

LBA is a mathematical scheme for addressing sectors, beginning at cylinder 0, head 0 and sector 1, which is equal to LBA 1. This scheme linearly maps the drive until the final physical sector is reached. LBA is efficient because it reduces some system overhead by not having to convert the operating system’s LBA to the BIOS CHS and then back to drive LBA.

2. What is CHS?

CHS stands for Cylinders, Heads and Sectors, this is the conventional means for BIOS to communicate to the drive. CHS has a limitation of 1,024 cylinders, 16 heads and 63 sectors per track resulting in a maximum capacity of 504 MB.

3. What is the difference between Normal, LBA or Large mode?

Normal mode is the standard BIOS translation scheme. This mode does not support drives greater than 504 MB. Large mode is a generic translation scheme used by some BIOS’s to access drives up to 1 GB. Logical Block Addressing (LBA) mode is a more advanced method of translation than Large mode. LBA mode is a somewhat faster and can see drives up to 8 GB.

4. What if the BIOS does not support the full capacity of the drive?

There are three possible answers to this question:

  • Upgrade the BIOS for the computers motherboard or replace the motherboard.
  • Add an Enhanced IDE card that has its own BIOS that provides support for large hard drives.
  • Install a translation software product such as Maxtor’s MaxBlast software, they’re latest version is 9.06M.