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Question

Where are startup instructions stored?

by Happy_Student / May 20, 2016 9:51 AM PDT

Hello, everyone. As I understand, the very first instructions CPU performs are startup instructions sent by BIOS, but I don't understand, where those instructions are stored. Also there are a lot of other things like: data for Power-on Self Test, data for activating other BIOS chips on different cards (for example: SCSI) etc. I used to think that all this data's stored in CMOS, but recently I read an article that said that modern CMOS is only responsible for time and date.
I really appreciate your help!

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All Answers

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Answer
For this we would need a classroom and more
by R. Proffitt Forum moderator / May 20, 2016 10:23 AM PDT

More than what will fit here. As to the modern CMOS that's a confusing term when we have to cover dozens of PC designs from the early 8088 to today's EFI model.

All this is on the web but I can't condense it here. Can you slim down your question or tell why this came up?

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Thank you for your reply
by Happy_Student / May 20, 2016 10:36 AM PDT

I read that CMOS had a lot of responsibilities in the past, but recently it lost most of its functions and now it's only responsible for time and date. I couldn't find myself the answer to my question, so I decided to ask it here (purpose: trying to learn how computer's hardware works). I realize that it's really complicated, but is there any way you could explain this in a nutshell? I'm not interested in UEFI yet, at first want to understand BIOS. Sorry, I can't freely express my thoughts . I'm 13 and English is not my first language.

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Again, there's a lot to read about all this.
by R. Proffitt Forum moderator / May 20, 2016 12:26 PM PDT

Once in a while I run into folk that think it can be summed up in a paragraph. Well, not this one.

You would not need to know all this today but use this as your starting point and take classes in electronics and more. Along the way you'll get into computer design which has changed a lot since my first computer (the GE-210.)

The BIOS is out there to read more. Examples:
https://simple.wikipedia.org/wiki/BIOS
https://en.wikipedia.org/wiki/BIOS for deeper reading.

Then we have CMOS. CMOS is not a thing but a technology of chip design. As an electronics designer you would wince at call CMOS the storage area for BIOS settings. But you let that slide and listen to the questions.

Lots to read out there.

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Answer
Too deep
by Willy / May 20, 2016 10:31 AM PDT

The CMOS and BIOS are basically the same item/device of IC buried on the PC, regardless of what type of PC. Also, these instructions aren't meant to be rehashed other than supplied by the maker of the PC or BIOS chip supplier. These instructions are so basic and totally accessed at early boot-up to ID the h/w within the PC, it really defeats its purpose to reqork unless you know the overall design and have a working ROM burner and of course all the code and/or burn(or update) the new ROM code. Let's be clear unless you have technical bkgrd. or access to these instructions, you just going to hose the PC. Understand most instructions are intended for the long run to be specific to the PC being build or its "chipset" foundation. I don't see an OEM or IC BIOS rom info being supplied for direct access other than supported bios updates. If you plan to reverse engineer, then you need the equipment to proceed as I state above.

tada -----Willy Happy

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Answer
Briefly
by Bob__B / May 20, 2016 8:28 PM PDT

The instructions/code are stored in the rom section of the bios.
They are read out and executed by the cpu.
You have no access to this.

Cmos is in the ram section of the bios.
That you can access and change stuff.

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Correction
by Bob__B / May 20, 2016 8:45 PM PDT
In reply to: Briefly

Cmos is not part of the bios it's a ram chip the bios uses.

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Correction to the correction
by Bob__B / May 20, 2016 8:58 PM PDT
In reply to: Correction

The instructions/code are stored in the bios.
They are read out and executed by the cpu.
You have no access to this.

Cmos is not part of the bios it's a ram chip the bios uses.
That you can access and change stuff.

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Answer
see the article
by renegade600 / May 21, 2016 2:36 AM PDT

see the following article and it will give you more info about the bios.

http://computer.howstuffworks.com/bios.htm

if you are able to, please provide the link to the article you read so we can have some context.

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