Hi Pete
I would have to look up the documentation relating to the various PCs that I have owned to get you the exact info from the manuals (and my personal notes), but here's an extract I found after a quick search:
http://www.duxcw.com/faq/cmos/cmos.htm"The CMOS memory is usually located with the real-time clock in the motherboard chipset or in a separate real-time clock chip. It is located in the chipset on most recent motherboards. For example, the CMOS memory is located in the VT82C596B Southbridge chip in the VIA MVP3C chipset on the Epox MVP3G2 Super7 Motherboard and in the AMD-756 Southbridge in the AMD-750 chipset on the MSI MS-6167 Athlon motherboard."
The references to Southbridge describes one of the main chips that comprise the "Chipset" of any Motherboard. You will find a Northbridge and Southbridge chip on standard motherboards, although one or both may have its own stuck-on heatsink preventing you from seeing the writing on it/them. These chips each have different responsibilities and act as I/O controllers for the various Buses like IDE, USB, etc.
If you look at the chipset description and layout diagram for a motherboard, you will see what they each do and may see which one the RTC (and also usually the CMOS RAM memory) is contained in.
From the point of view of visibility, on very old motherboards you may see a separate chip often marked "Dallas". This is the RTC/CMOS chip. The expression "CMOS Chip" is something of a misnomer when speakng of modern motherboards because it is usually integrated into the "chipset" somewhere where you cannot point at it with a pencil and show off to others how well versed you are with the location and function of all the visible chips, sockets and pinouts :-)
When discussing the difference between "CMOS" and "BIOS", the writers of motherboard manuals are probably the worst culprits for causing this ambiguity and misunderstanding. They always place the section about the CMOS Battery and the tables showing the CMOS Settings right next to instructions for Flashing the BIOS, and refer to the CMOS Setup Screen as the "BIOS Setup". Another misnomer is CMOS Setup "Program". The CMOS memory cannot hold directly executable code, only settings, so "program" is incorrect terminology. In context with the ability to enter a set of screens that allow you to change and Save configurations, then I suppose you could loosely refer to the function as a "program".
Interesting fact:
You may be aware that most HP/Compaq computers use F10 key to enter the CMOS Setup. At one point (I would have to look back but it would be around 1997) Compaq created a very small hidden partition on the system drive of their PCs. This is often referred to as the "F10 Partition". The main reason they did this was because, while other manufacturers introduced CMOS memory with a greater capacity to hold the myriad of settings created by necessity through advanced technologies, Compaq kept theirs to the smaller storage capacity. To enable users to view and modify the advanced CMOS settings, they had to store a few small programs on this hidden partition.
2nd-owners of these units often used a low level format or partitioning utility to wipe and repartition the hard drive, destroying the "F10" partition, so Compaq had a download in the form of an executable that created bootable floppies. One was for the recreation of the partition on an unpartitioned drive and the other was to copy the essential tools to this partition so that the F10 key could access them and display the CMOS settings.
Once partitioned using the bootable floppy, the standard DOS FDISK could then create normal visible partitions without interfering with the F10 Partition, but it was impossible to create the hidden F10 partition on a drive that had already been partitioned using FDISK or similar utilities.
There is usually an option in some older Compaq computers (Pentium 3 era)that have standard CMOS memory to Save the CMOS Settings to Floppy, or to Load them from Floppy. If you have ever seen the output, most of it with the exception of the ESCD it is standard text that is visible in the example attached (CPQSETUP.TXT).
ESCD (Extended System Configuration Data) is really the remembered settings from the last boot, and the settings are capable of being reconfigured automatically if you eg. add more memory or add another Plug and Play device.
From the pages of one of our own esteemed experts (as far as I can see:
http://www.experts-exchange.com/M_306968.html)
:
http://www.dewassoc.com/support/bios/escd.htm
