Hardware Reference
In-Depth Information
and functional. If nothing at all happens, the recovery may have failed, or the board may not feature a
separate boot-block section (which contains the recovery code).
Note
The BIOS recovery procedure is often the fastest way to update a large number of machines,
especially if you are performing other upgrades at the same time, or the machines are new and
do not have a bootable OS installed. For example, this is how updates are sometimes done in a
system assembly or production environment.
Motherboard CMOS RAM Addresses
In the original IBM AT system, a Motorola 146818 chip was used as the real-time clock (RTC) and
CMOS RAM chip. This special chip had a simple digital clock that used 14 bytes of RAM and an
additional 50 more bytes of leftover RAM in which you could store anything you wanted. The
designers of the IBM AT used these extra 50 bytes to store the system configuration.
Modern PC systems don't use the Motorola chip; instead, they incorporate the functions of this chip
into the motherboard chipset (South Bridge) or Super I/O chip, or they use a special battery and
NVRAM module from companies such as Dallas Semiconductor or Benchmarq.
Table 5.1
shows the standard format of the information stored in the 64-byte standard CMOS RAM
module. This information controls the configuration of the system and is read and written by the
system setup program.
Table 5.1. CMOS RAM Addresses
