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im new to this forum but i get confused when people are like "Uhh yeh i can upgrade CMOS without causing damage to the random access memory" which i understand, but what is CMOS? There dont seem to be any wiki articles about it either sigh :P

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migrated from stackoverflow.com Oct 28 '10 at 19:24

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Are you talking about the transistors? en.wikipedia.org/wiki/CMOS –  PigBen Oct 28 '10 at 16:06
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Is this really related to C++ / Programming ? –  nos Oct 28 '10 at 16:07
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Who says "Uhh yeh i can upgrade CMOS without causing damage to the random access memory" other than on some sitcom about geeks? And how do you "upgrade CMOS"? Do you mean reflashing the BIOS? –  Praetorian Oct 28 '10 at 16:10
    
Sounds like homework. –  Drackir Oct 28 '10 at 16:13
    
This might be better suited for electronics.stackexchange.com (but I can't really tell...) –  Kevin Vermeer Oct 28 '10 at 21:34
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6 Answers

http://en.wikipedia.org/wiki/Nonvolatile_BIOS_memory

(Note that in the context you're using, CMOS is an incorrect use derived from the CMOS technology.)

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The wording suggests they meant upgrading the BIOS. BIOS is a piece of code that gets control when you turn the computer on. It does self-tests, initializes some hardware, then loads the operating system.

In the olden days, there was a block of writable, power-independent data that the BIOS code used to store things like current time, hard drive configuration etc. This was before the advent of flash memory, so the said data block was stored in a CMOS technology chip (see above for technicalities), and backed by a battery. Since the interactive parts of the BIOS would refer to this data as "CMOS memory" (which it was), there came to be a confusion between BIOS and CMOS. Repeat: BIOS is code, CMOS memory is where it stores its persistent data.

Since BIOS is stored in rewritable flash memory these days, as opposed to read-only memory of old, yes you can upgrade it.

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CMOS = Complementary Metal-Oxide Semiconductor

It is a particular way of constructing semi-conductor chips.

I'm not sure how that applies to 'upgrading CMOS'.

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http://en.wikipedia.org/wiki/CMOS

CMOS is a manufacturing process, so "upgrade CMOS" doesn't make sense. They probably ment "upgrade BIOS", which is common since a lot of motherboards are shipped with buggy firmware that is patched with downloadable updates later. I still can't see why it would damage your RAM, though.

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As Jonathan Leffler says, CMOS is a way of fabricating chips. CMOS uses pairs of FET transistors. The effect is a circuit that works on voltage instead of current (as used by conventional transistors). Hence it is possible to construct very low power CMOS circuits. The downside is that they tend to be susceptible to static electricity, which is probably where your warning comes from. Although most CMOS chips have anti-static protection circuity built in, it is still generally a bad idea to touch the pins with your fingers unless you and the circuit are properly grounded.

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CMOS memory chips take very little power. I don't know if this is still true, but at one time most PCs used CMOS memory to hold the computer's configuration information, and NMOS or other technologies for the "regular" RAM for running programs. By "configuration information" I mean the data that the computer needed to boot up but which should be user-settable, like which drive to boot from. That is, the data that you see when you hit the "setup" key during power-up. A small battery is sufficient to keep the CMOS data alive while the power to the computer is turned off.

Thus, many people have come to refer to this boot configuration data as the "CMOS setup" or similar terms.

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