He is the first code run by a PC when powered on!
He communicates with the hardware and the operating system!
I would like to know if he is the CENTRAL element in a PC? I mean is he connected to all the input/output devices? (Address, data and command)
Thank you

First, its not "he". He and she refer to male and female living organisms, usually higher level mammals like humans. The proper pronoun is "it". The BIOS is a "thing", not a person.

A little English lesson never hurts, otherwise, you won't get better at it And you will sound like Borat

In any event, BIOS is software, its the startup software for a computer or embedded system. When the computer is powered it, its nothing more than a microprocessor connected to external memory (RAM and ROM). Thus, you need to have bootstrap or start up code that gets the computer going and has "BASIC" input and output functionality. This is what BIOS does. On early PCs BIOS was much more important since operating systems like DOS actually used the code in BIOS after the start up of the computer. Now, BIOS simply boots the computer and then loads in the command or OS kernal which takes it from there. And in many case, modern OS's do NOT use any functions from BIOS.

So, the bottom line is when a computer boots, the processor goes to a SPECIFIC location in memory and starts executing code, this is where the entry point of the startup system/boot system is. Then early PCs BIOS stored a library or API of functions to help OS authors communicate to the hardware via a hardware abstraction layer. But, these days this is rarely needed, but is still there for legacy and backward compatibility.

Therefore, to answer your question -- BIOS is software, it is NOT connected to anything. The computer is the computer, it has a microprocessor, buses, and interfaces, then the startup code runs which has a library of functions burnt into ROM called BIOS, this software KNOWS about the hardware and thus can command the hardware, but its not connected in any way. Hardware is accessed via hardware interfaces, memory mapped IO, or IO mapped channels, ANY code can access it; BIOS, the OS, a game, whatever -- its just that years ago, when you wanted to write a byte to the CD, there weren't device driver models, there was a BIOS driver model, and thus you would call an interrupt or a BIOS service by vectoring your code (making a jump or calling and ISR) and then this would call the BIOS API for writing a byte, or whatever. And how you talked to the API was thru register and or stack space based on an agreed set of variable and data structure conventions.

Andre'

Thank you very much Mister André! You are the best teacher.
Now I have a clear idea about BIOS.

I suggest reading this book:

http://www.amazon.com/Bios-Programmers- ... 946&sr=8-1

I think I read this about 20-25 years ago

And this by the biggest developers of BIOS chips:

http://www.amazon.com/System-BIOS-IBM-C ... 000&sr=8-4

And finally, these three series:

http://www.amazon.com/Upgrading-Repairi ... 000&sr=8-3

http://www.amazon.com/Winn-Rosch-Hardwa ... 143&sr=1-1

http://www.amazon.com/Peter-Nortons-New ... 184&sr=1-1

I have dozens of these kinds of books, I have read them all many times, there is no substitute for reading this stuff, only by understanding computers from the start, can you understand them now.

The problem with everyone now is they have "surface" knowledge, little tidbits of information from internet, articles, wikipedia, you want to really OWN this stuff ? Then you need to sit down, and read these books and more cover to cover for DEEP understanding.

It takes a long time, but I can usually get thru a 1000 page book in 2-3 days, that's what I used to do. When I wrote books especially, I would read a LOT of books at the same time, but if you start and stop, you will never finish any books, you need to do them straight thru.

But, these questions you have are very basic, and you just need to read these books or similar and you will know everything about it.

Andre'

I will, Thanks