I had a feeling it might be a good thing to give you readers some background about computers and how they work.
this information is not specific OS(Operating System) related or company related, this is the way nearly every piece of hardware in the world works.
you might say "so what? I don't care what happens "under the hood" of my windows, I just want to know how to make things work", well, you are right, this is a very important issue, but still - understanding the basics is... well... the base of all problems solving, don't worry now, this wont be long (I hope :) )
"How does my computer boot" or... "what happens from the second I turn the computer on untill the OS logo appears"
as most of you know, whenever you turn your computer on, the computer gives a small "bip" sound, counts the RAM memory and gives us an option to enter some wierd menu (usually the message would be "press "Del" key to enter BIOS Setup")now then, lets review:
the BIOS, which stands for "Basic Input/Output System", is the first thing that goes up when the computer is powered on, its primary function is to identify and initiate component hardware, the small "bip" sound tells us there are no crucial errors with the motherboard, cpu and display adapter (each hardware has its own distinguish "alarm" sound which'll indicate why the computer isn't working properly)
the BIOS has some more functions, msot common among them are HDD list connected to the motherboard, boot sequence (allowing the computer to boot from floppydisk or CD ROM rather then local hard drive), large memory support (for systems with over 3.5GB of RAM installed) etc. etc.
since the BIOS isn't a part of the Operating system, and it should recognize the HDD itself, I suppose its pretty obvious, but I'll say it anyway - the BIOS isn't piece of software, its a chip welded to the motherboard.
What next?
well, not much left, because the BIOS did nearly all of our job, it detected the basic hardware on our computer, made sure its good to go, descided where to boot the system from (boot sequence, remember?) and told the computer "boot up from floppy/cd/1st hdd/2nd hdd/usb/network (delete the unnecessary)"
lets say the first HDD was chosen, now the question to be asked is "how does the computer find the Operating system?"
it sounds like an easy question ("simply find the XXX file and run it"), well, basically its true, but what if the HDD is divided to 5 different partitions? with 5 different copies of "Windows XP" to run? and how does the computer knows which file to run? he's not THAT smart, and that system works for over 20 years!
well then, lets begin with some (more) background and move our way up from there.
HDD, or any storage media for that matter is basically divided to cells, each one with its on unique number (called "address"), and each one can hold a file or a part of it.
the most important cell in the HDD is the first one, cell addressed as number 1, it even got its on cool name, "MBR", or "Master Boot Record", this cell isn't holding any file, it hold a pointer to the OS boot file (or "cell address" of the Boot Loader (the application that run the OS))
so in the most common example of 1 computer with 1 HDD with 1 partition the BIOS will tell the computer to load from the 1st HDD (as no other is present), and its MBR will point us to the correct boot loader.
now lets get a little more complications in the equasion, and divide our HDD to 5 partitions
now what? how does the BIOS knows which one to load?
well, the secret is, the BIOS doesn't really know the HDD is divided, it still tells the comptuer to load from the MBR, which points us to the boot loader, only this time the boot loader is smarter, it gives us an option to select from which partition to load the OS, but its not a part of the BIOS.
in case of several HDD's, its a little bit different, the BIOS will be the one to tell the computer where to boot from (remember? 1st HDD, 2nd HDD etc.), only after that the MBR'll kick in and load the boot loader.
whew, that was long enough, and not a word on windows... maybe in the next post :)
till then - take care (and leave some comments!)
This blog have been moved to http://ponline-space.net/
hope to see you there!
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