|Nov26-10, 11:10 AM||#1|
BIOS chip and CMOS chip
I have some trouble understanding the CMOS chip and the BIOS chip. Some of the terminology throws me, for instance when "go into CMOS" and "go into the BIOS" are used interchangeably.
Here's how I think it works:
The BIOS chip:
A "system rom" chip, non-volatile memory
Contains firmware that can be updated by "flashing the BIOS", but is done rarely
Contains the BIOS (instructions for checking hardware and starting an operating system)
Contains a "CMOS set up utility" for changing BIOS settings
The CMOS chip:
Volatile memory, persists as long as it has battery power
Contains the BIOS settings (things like boot order, and user and supervisor BIOS passwords)
Holds date and time information
Am I on the right track?
I got further confused last week when a friend was telling me that the BIOS chip and the CMOS chip are the same thing.
|Nov26-10, 11:16 AM||#2|
The terminology is mostly wrong - it comes from people building cheap clones copying each others documentation and stuff that is just out of date.
The bios (a program) used to be stored on an eprom with the settings stored in a low power memory (CMOS) which was kept alive by a little watch battery on the motherboard - which also powered the clock when the computer was turned off.
Now the whole thing, the bios program and the settings are stored in flash memory (the same stuff as your usb key or memory card) this makes it much easier to update the bios program to a newer version. You generally don't bother unless there is a specific fault that the new version fixes or some useful feature - if it ain't broke ....
Similalrly there are a 100 and 1 tuning parameters on a modern PC - especially a high performance one which allow you to tweak it's performance. Unless you have no life and enjoy spending the weekend adjusting them so that your machine is 1% faster than some other loser's on the internet - you just select 'default' in the setup screen.
However none of that matters.
You go into the setup screening by hitting whatever magic key combination at startup.
If you have screwed up the machine that it won't boot there will be a jumper somewhere on the motherboard that says "bios reset" or "cmos reset".
Pulling the battery out doesn't necessarily clear the settings anymore
|Nov26-10, 11:49 AM||#3|
So, what is the battery powering if the BIOS plus the settings are all stored in flash memory?
|Nov26-10, 12:00 PM||#4|
BIOS chip and CMOS chip
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