advice re CMOS please

  david.h 18:51 10 Sep 2003

I have just entered my BIOS and noted all the settings, is the cmos battery where these settings are stored or are there additional settings in the cmos if yes how do i access my cmos to note any settings.

to access the bios i pressed F1 on start up on a gateway computer

  mark500 18:57 10 Sep 2003

CMOS Explained
What is it?
CMOS is simply some memory that has battery backup so that it maintains its state between power cycles.

It is part of a chip that can be seen in your computer. Its part number is usually MC146818.

Why is it?
Information about the make up of the system needed to be retained between power cycles so that the system could boot properly. CMOS was designed to maintain that information in the simplest manner possible. It also had to be modifiable in the event that the make up of the system changed. Its design also mandated that a machine come from the factory with the CMOS configured to reflect the make up of the system at the time it was shipped.

What can it affect?
Date and Time on your computer
Floppy Drives
Hard Drives
Memory Check at POST
How is it set?
The CMOS is set at the factory so that it conforms to the configuration shipped. During the boot procedure you can stop the process and change this. Usually a message indicating how this can be done will be help on the screen for a few seconds so that you might do this.

There are also ways to read and write this memory from a programmer's standpoint.

Access via the BIOS
Access via Address and Data Registers
Access via the BIOS
This method limits you to the DOS clock and the real-time clock. Here is an example:

mov ah, 03h; function 03H
mov cl, 45h; 45 minutes
mov ch, 12h; 12 hours
mov dl, 00h; no daylight saving
mov dh, 00h; 0 seconds
int 1ah ; set time via interrupt 1ah

Access via Address and Data Registers
IN al, 70h; read old byte from port 70h
AND al, e0h; clear the five low order bytes
OR al, 12h; load accumulator al with address
; of byte 18, bit 7 remains unchanged
OUT 70h, al; write address of byte 18 into address
; register
IN al, 71h; read drive type into accumulator

  david.h 19:46 10 Sep 2003

i cant find any address or data register access in the bios.
if i cant find it to write it down can i back it up to a floppy somehow.

  Rtus 20:06 10 Sep 2003

For the ordinary user (no disrespect intended) Looking at their Motherboard manual explains what the settings /options for the bios setting are.
The CMOS battery only enables the Bios chip to be powered while your not using the computer ,thereby retaining the settings for the next boot-up . The easiest way is use the manual as a guide enter your units bios then tick /underline which is set at what for each entry..retain for future reference..
If you haven't access to a Motherboard manual Jot all the settings down for each section and file away for later..

  david.h 20:56 10 Sep 2003

thank you i have noted all the bios settings , i have no manuel for the motherboard that the problem with shop built systems, should i note any cmos settings or are they the same as the bios as i cannot find access to cmos [still a novice in this area, a lost one at that but trying to learn]

  Rayuk 21:02 10 Sep 2003

The cmos stores all your bios settings,battery provides the power to save the settings when your pc is switched off.

Do not bother yourself with it.

If you know your motherboard make and model you can download the manual from their website.

If you need to find out model download
Aida32 Personal System Information

click here

  david.h 05:15 11 Sep 2003

thankyou all for helping

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