Howdo: From 'ON' button to your desktop

Original blog at: http://iahmyi.blogspot.com/2010/12/howdo-from-on-button-to-your-desktop.html

Howdo the new tag I brought up. Something I figure a relative thing to blog about. People know what it is but do we know how do it? For instance the Play Station (PS) how do it run smoothly when I play my games. Or questions such as how do I get into my friends iPhone without him noticing it? Al on how do topics we will spread it out. If any of my posts have differ from what it suppose to I am sorry. Maybe the way I explain it wrongly. Thats the main thing of having greater imaginery and visual brain reaction. By now maybe you guys now know why I write these blogs?



For my first how do post, I am going to talk about how do it all works from on switch / button to your desktop. Why desktop not your OS (operating system)? I don't know. Maybe sounds catchy rather then long words such as Operating System. Or specific words such as KDE. Or the computer GUI. Other than that I figure everybody knows what a desktop is cause all OS has one. Even the TUI(text base user interface) base system has one. Its just the way it is being exposed for users differently. I remember back in those days when my father has this personal computer (PC) which runs to TUI before the GUI loads up. You got to select what you want to do first. Something like

Menu:
Start *******
Format Disk
.......
Please select your choice:
|

'|' is a blinking cursor.

This is actually what I call it as desktop also. Even though it doesn't go specifically to users' login account desktop somehow I see it a desktop of the system before users own desktop. Now a days once your system boots up it goes directly to the specific desktop with icons, application or directory. For instance if we look at mobile phones this is its desktop.

Enough bla bla bla. Lets go to the real deal. We know that a computer can operate many operating system's desktop such as Windows, Linux's distros and many more. Computers here means computer!! Not PC or laptops only but also mobile computer in which phones are among it. I will expose the how do it operates on unix family. When we are talking about unix family this includes Linux's Distros and also the Darwin Mac Os X and iPhone Os (even though there are some difference in most unix family OS but basicly this is how it works).

Before we press the 'ON' switch what do we know? Nothing I figure. Ops maybe the switch looks different compare to my phone and my laptop. Other than that..hmm. Nothing. Well thats what we see on the surface. The main function of this 'ON' switch is actually to bootup your computer by sending out a 1 voltage signal (not 1 Volt), thus, as Dr Frankenstien would say, “ITS ALIVE!!!!”. Your processor running, your CDROM blinks, your monitor flicks, your optical mouse lights up, your keyboard's cap's lock, num lock or other led indicator blinks and dies out. Whats happening at this short period of time (slow processor be longer) is that the BIOS (basic input/output system) identifies the functionality of your computer peripherals. On older phones you can see that the keypad lights up a sec before you see the logo and the teeee neeee neeee neeee sound. If you are an electrical engineering student the PIC programming or the assembly (.asm) language used to light up a LCD is something similiar to this BIOS.

Then BIOS tells your boot device to run. So its like, Frankestien is alive and being told buy Dr Frankenstein to make some coffee. To tell which boot device is usually setup on your bios screen that prompts at the bottom of screen “F12 boot device” or sometime alt+del, F2 or del. Depend on your own x86 computer (this the average PC). Some BIOS doesnt have a bootscreen. Here are how some bios boot screen looks like.

After bios, theres the master boot record (MBR). This guy is usually designated on your boot device. Mostly your hard disk unless you bootup to your desktop using floppy disks. Bootstrapping to your OS, after the computer's BIOS passes execution to machine code instructions contained within the MBR. There are many types of bootloader from here. Such as GRUB, LILO, DOS and many more. So what it does is tell what to do to start your OS then to your dekstop. Since I am using GRUB as my bootloader I will go on depth to this part. What GRUB usually do is identifying the image of your kernel and other configuration on /boot/grub/. In the Windows world maybe some of us never heard of such term. The issue of a system booting invisible, unless you use the old version of windows. So nothing much we non-IT literate users been spared on learning or knowing the most important part and how it works.


We've talked about kernel before. Right after GRUB. So whats a kernel? Since my new job this new year (refering to gregorian calendar) is more on kernel development (maybe) I will briefly describe what Linus Torvalds has done on upraising the LINUX world. Kernel reacts as a bridge for any OS to communicate with the hardwares. Every kernel on different platforms differ to what they do. For example the Windows NT kernel design consists of two main components, user mode and kernel mode.Basically it initialize devices for usages. Here is a pic of my kernel ring.

After that? Init. This is something like my previous post http://iahmyi.blogspot.com/2010/12/init-hacked.html. Init stands for initialization. If you look at your process status id no 1 you will see it is your init. So you can guess this is your infinite loop for the system thats used. Going to run levels and to your desktop.

Wah penatnya (exausting).  Theres a lot more going after that. I think this is the only thing I am going to write. By the way if theres any errors on my way of spitting out howdo it works feel free to tell me.