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The ROM and the CMOS


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#1
coasttech

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I am in school now and the teacher was not very helpful with this.

Ok I donít understand what the differences is between the ROM and the COMS..

"BIOS consist of software instructions stored in a hardware component, and CMOS is the physical component the BIOS is stored on."

So the CMOS is a physical thing on my MoBo that holds the BIOS ...I know that.

But I also know that the POST instructions are stored on the ROM.


So is that a whole other chip or is it built into the CMOS?
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#2
Kemasa

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The CMOS is a battery backed up memory which stores the settings from the setup menu.

The BIOS is the program which is the initial program to get the machine going, it is not stored in the CMOS since if the battery died, then you would be SOL. It is often a EAROM or EPROM, which means you can re-write the data, but it is slow.

ROM is read only memory, but this is generally not used anymore since it is hardcoded when it built and can not be changed. This is replaced with devices which can be changed, like the EAROM or EPROM.
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#3
coasttech

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So the BIOS is on the EAROM or EPROM?
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#4
Kemasa

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Yes, it is the software which is written into the EPROM, EAROM or whatever other device the board manufacturer decided to use.
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#5
coasttech

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Would those boards still have CMOS?
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#6
Kemasa

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Yes, the CMOS is used for storing the date and time and other settings which often change, which is quicker and easier to do with a battery backed up memory device rather than having to take the time to write the device. Also, many devices have limits as to how many times they can be written. The BIOS is rarely updated, so that is not an issue with that.
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#7
coasttech

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man ....what the [bleep] are they teaching me there ....sigh

Can anyone second what Kemasa is saying?

Edited by coasttech, 14 February 2006 - 10:54 PM.

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#8
Kemasa

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Ok, so you don't believe me, check out these links and follow the links on the pages for more information:

http://www.pcnineone...biosflash1.html
http://www.computerh...es/ch000707.htm
http://www.computerh...rgon/b/bios.htm
http://www.computerh...rgon/c/cmos.htm
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#9
coasttech

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DudeÖ itís not that I donít believe you. I am just going off of what I am learning at my collage. I am also preparing for my CompTIA exams. So I am just confused with what seems to be garbage what my school is teaching me.



....and reading that stuff now
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#10
AcidWarp

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Okay, Coasttech is a good friend of mine, and has asked me to explain CMOS and BIOS to you all.

In short, the BIOS (Basic Input/Output System) is stored ON the CMOS chip. CMOS is simply a type of semi-conductor chip. IIRC it stands for. Complementary Metal Oxide Semiconductor. That's it, literally. The TYPE of CMOS chip is a programmable EEPROM, that's why you can edit parts of the BIOS (change low-level settings like ram timings etc). There is a non-writeable portion that stores some very basic information like the BIOS bootblock and the bootstrap information.

All the battery is used for is to save user changes, and to keep the clock running. You can take the battery out and the system will still run fine (usually), as long as you leave it plugged into power. The user changes AREN'T saved when you remove the battery because of the nature of the CMOS chip, it's not like a Compact Flash card or something.

I recommend the following article on wikipedia as a primer on CMOS.

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

Edited by AcidWarp, 14 February 2006 - 11:33 PM.

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#11
Kemasa

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Sorry, but your information is not completely correct. You are correct that often the EEPROM is used (many different types of memory devices).

The BIOS is stored on a different chip and it is writable, search for flashing the BIOS.

An EEPROM type of device needs no power to retain the settings, but that is not what is used for the settings from the setup menu.

Read the links that I posted.
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#12
Kemasa

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DudeÖ itís not that I donít believe you. I am just going off of what I am learning at my collage. I am also preparing for my CompTIA exams. So I am just confused with what seems to be garbage what my school is teaching me.
....and reading that stuff now


Welcome to the state of education in this country. The old saying is that those that can do, do, those that can't teach, and those that can't teach administrate.
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#13
AcidWarp

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Believe what you want, I know I'm correct.
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#14
Kemasa

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Interesting. Do you happen to know why CMOS is used rather than other types of chips, such as TTL?

Since you claim to be correct, could you explain why there is a need for the battery to retain the settings, but not for the BIOS itself?

While it is possible to put multiple type of devices in a single IC, it is not typically done unless there is a real need for it.

But, to put the question to rest as to who is right and who is wrong, one need only refer to the links I included above, which were found with a web search (to confirm what I already knew). Make specific note of "the BIOS and CMOS are two different components on the motherboard" in the paragraph below.

With this, could you provide some documentation that what you say is correct? Or are you willing to admit that you are not correct?

http://www.computerh...es/ch000707.htm

Question: What is the difference between BIOS and CMOS?

Answer:

Often the BIOS and CMOS can be confused because instructions may either indicate to enter the "BIOS Setup" or the "CMOS Setup". Although the setup for BIOS / CMOS is the same, the BIOS and CMOS on the motherboard are not.

If you have already read the above BIOS and CMOS definition links you should now know that the BIOS and CMOS are two different components on the motherboard. The BIOS on the motherboard contains the instructions on how the computer boots and is only modified or updated with BIOS updates, the CMOS is powered by a CMOS battery and contains your system settings and is modified and changed by entering the CMOS Setup.

Although the setup is often referred to as the BIOS and CMOS setup, we suggest you only refer to the setup as "CMOS Setup" as it is more appropriate. Computer Hope often refers to the setup as BIOS and CMOS Setup to help users who are looking for one instead of the other.

BTW, the other links might help you be a bit more educated :-).
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