Computer starts, its system attributes—stored in the CMOS RAM—are read by the BIOS. BIOS then uses those attributes during normal system operation. It is vitally important that the correct settings be used when configuring a system.
BIOS and CMOS RAM are not the same thing, although the two are intimately related. BIOS refers to the firmware instructions located on the BIOS ROM, and CMOS refers to the low-power RAM that is holding the system’s setup parameters. BIOS reads the CMOS RAM into memory at start time, and provides the “setup” routine that allows you to change the contents of CMOS, but the CMOS RAM/RTC device is a totally different IC.
ENTERING CMOS SETUP
The configuring of CMOS setup is to launch the setup utility. BIOS manufacturers are rarely consistent when it comes to accessing the setup utility. we launch Setup in the first few moments after the system boots—a note on the display will usually indicate the correct key or key combination such as:
Press <F1> to enter Setup...
BIOS/SYSTEM KEY OR KEY SEQUENCE
AMI BIOS <Del> key during the POST
Award BIOS <Ctrl>+<Alt>+<Esc>
DTK BIOS <Esc> key during the POST
IBM PS/2 BIOS <Ctrl>+<Alt>+<Ins> after <Ctrl>+<Alt>+<Del>
Phoenix BIOS <Ctrl>+<Alt>+<Esc> or <Ctrl>+<Alt>+<S>
ALR PC <F2> (for PCI systems)
or <Ctrl>+<Alt>+<Esc> (for non-PCI systems)
Compaq PCs <F10>
Gateway 2000 PC <F1>
Sony PC <F3> while the PC is starting (you see the Sony logo), then hit <F1>
THE CMOS MAP
standard 128-byte ISAcompatible CMOS is divided into four fairly distinct sections: 16 bytes of real-time clock data (00h–0Fh), 32 bytes of ISA configuration data (10h–2Fh), 16 bytes of BIOS-specific configuration data (30h–3Fh), and 64 bytes of extended CMOS data (40h–7Fh). Additional CMOS
RAM is typically used as the ESCD.
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