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Please Tell me the difference between BIOS and CMOS. I understand that BIOS is ROM and CMOS is
RAM which is supported by a battery.But are these two physically different chips and what is
function of each one.When we enter in "SETUP" at start up of computer where these changes are
stored,i think in CMOS. Where these two are located on motherboard , If u know any good site
which explains all this in detail give me thanks.:confused: :no:
 
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What is BIOS?
BIOS stands for Basic Input Output System.


All computer hardware has to work with software through an interface. The BIOS gives the computer a little built-in starter kit to run the rest of softwares from floppy disks (FDD) and hard disks (HDD). The BIOS is responsible for booting the computer by providing a basic set of instructions. It performs all the tasks that need to be done at start-up time: POST (Power-On Self Test, booting an operating system from FDD or HDD). Furthermore, it provides an interface to the underlying hardware for the operating system in the form of a library of interrupt handlers. For instance, each time a key is pressed, the CPU (Central Processing Unit) perform an interrupt to read that key. This is similar for other input/output devices (Serial and parallel ports, video cards, sound cards, hard disk controllers, etc...). Some older PC's cannot co-operate with all the modern hardware because their BIOS doesn't support that hardware. The operating system cannot call a BIOS routine to use it; this problem can be solved by replacing your BIOS with an newer one, that does support your new hardware, or by installing a device driver for the hardware.


You can change hardware configurations that are stored in the CMOS, or Complementary Metal Oxide Semiconductor.


To perform its tasks, the BIOS need to know various parameters (hardware configuration). These are permanently saved in a little piece (64 bytes) of CMOS RAM (short: CMOS). The CMOS power is supplied by a little battery, so its contents will not be lost after the PC is turned off. Therefore, there is a battery and a small RAM memory on board, which never (should...) lose its information. The memory was in earlier times a part of the clock chip, now it's part of such a highly Integrated Circuit (IC). CMOS is the name of a technology which needs very low power so the computer's battery is not too much in use.
 

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Not that it's terribly important, but I believe CMOS stands for Complimentary Metal Oxide Semi-conductor.

I thought the BIOS lived on the CMOS. Is this incorrect?
 

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Ok I have a lot of time today so here's my input, well from what I'm studying anyways
"In reality, CMOS no longer exists. Flash ROMS now hold both the system BIOS and the CMOS settings. Although the CMOS chip may have gone away, its legacy lives in even the most modern systems. All techs still call the setup program the CMOS setup program, even though we know the data is now stored on flash ROM. Many BIOS still say the word CMOS at the top of the screens, even though CMOS is long gone. Most systems still use a battery, although its job is relegated to nothing more than keeping the clock running when you turn off the PC."
So it seems that CMOS is not really RAM but flashable ROM. Pretty scary with some of the viruses out there that will flash your BIOS useless. Oh I also read that sometimes the CMOS battery is actually on the chip itself. Thankfully it did say that the battery last a long time! Whew!
Don't forget that some BIOS is actually on other devices like CD-ROMS. Yet, these devices only carry that for there own use and still rely on the system BIOS.
Whew! Thats the most of written in here for a while.
 

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mcgeeb - keep in mind, plenty of people (like me) still have old PC's in use. Not everyone can afford the latest and greatest.

Speedo - sorry! I did read your post - but brain not in gear! I need to get some more coffee! :coffee:
 
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Most systems still use a battery, although its job is relegated to nothing more than keeping the clock running when you turn off the PC."
I think it does a little more than that. Pull your battery out and start your machine and let me know what happens.............:winkgrin:
 
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sorry! I did read your post - but brain not in gear! I need to get some more coffee!
Oh BTW no sorry needed I have done the same myself I'm sure. It was just my way of saying Hey! Whatsa matta U........:winkgrin:
 

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Sorry guys. About the battery, it was just a quote. Also it wasn't in that exact paragraph that the battery "may" be on the CMOS chip itself. That whole paragraph is in all quotes from a book. Yes I didn't mention that it was about current BIOS and CMOS and that older computers don't have the exact scenario as what is in the paragraph, sorry. I'm still learning also and very still very eager to do so. I thought it was interesting stuff and that the thread starter would like to hear about it.

ps. I enjoy this forum and often read through your topics :winkgrin: I'm looking for a new job now, but can't find one since the economy sucks, so interestingly enough and looking through here to "see" the strange and unexpected problems with computers!!!
 

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"In reality, CMOS no longer exists. Flash ROMS now hold both the system BIOS and the CMOS settings. Although the CMOS chip may have gone away, its legacy lives in even the most modern systems. All techs still call the setup program the CMOS setup program, even though we know the data is now stored on flash ROM.
Your course needs some proofreading, because the data certainly isn't stored in FLASH! The BIOS is stored in the FLASH, and the BIOS parameters are normally still stored in battery backed RAM. Some systems, like many Acer systems, have EEPROM for a backup copy of the configuration, so if you lose the setup data, you can restore it.

The reason that the BIOS parameters aren't stored in FLASH is that FLASH is not byte erasable, it's page erasable, usually in pretty big chunks. EEPROM and RAM are obviously capable of reading/writing individual bytes, that's why they're used for parameter storage.

For a simple test, remove the battery from your system and wait at least 20-30 minutes and power it up. Let us know if more than the clock has been lost. :)

I don't get to use my EE hag much anymore, had to blow the dust off of it. :D :D
 
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