What will happen behind when you switch on your computer?

[KapilAsdhir]

What will happen behind when you switch on your computer?

[KapilAsdhir]

When you hit the power button on your computer a whole lot of stuff happens. We call this the boot process. In the days when I first started using computers there was literally a \"boot disk\", a floppy (5.25\" not a 3.5\") disk that told the system where to go and what to do so that the operating system would start up. Since then the boot sequence has become somewhat more complicated. So let me take you thru the steps the computer takes to get started. For my example I\'m going to use a Windows XP system.

1. First is the POST, this stands for Power On Self Test, for the computer. This process tests memory as well as a number of other subsystems. You can usually monitor this as it runs each test. After that is complete the system will run POST for any device that has a BIOS (Basic Input-Output System). An AGP has its own BIOS, as do some network cards and various other devices.

2. Once the POST is complete and the BIOS is sure that everything is working properly, the BIOS will then attempt to read the MBR (Master Boot Record). This is the first sector of the first hard drive (called the Master or HD0). When the MBR takes over it means that Windows is now in control.

3. The MBR looks at the BOOT SECTOR (the first sector of the active partition). That is where NTLDR is located, NTLDR is the BOOT LOADER for Windows XP. NTLDR will allow memory addressing, initiate the file system, read the boot.ini and load the boot menu. NTLDR has to be in the root of the active partition as do NTDETECT.COM, BOOT.INI, BOOTSECT.DOS (for multi-OS booting) and NTBOOTDD.SYS (if you have SCSI adapters)

4. Once XP is selected from the Boot Menu, NTLDR will run NTDETECT.COM, BOOT.INI and BOOTSECT.DOS to get the proper OS selected and loaded. The system starts in 16-bit real mode and then moves into 32-bit protected mode.

5. NTLDR will then load NTOSKRNL.EXE and HAL.DLL. Effectively, these two files are windows XP. They must be located in %SystemRoot%System32.

6. NTLDR reads the registry, chooses a hardware profile and authorizes device drivers, in that exact order.

7. At this point NTOSKRNL.EXE takes over. It starts WINLOGON.EXE that in turn starts LSASS.EXE, this is the program that display the Logon screen so that you can logon.

[confidant]

I remember the good ol' days when we had to use boot disks. Things sure have come a long way since then. I think it's great that now all we have to do is push a button, and were ready to go. Windows even runs automatically now. I remember when I had to use DOS commands to run windows.
security credentials

[nobita_deptrai]

As KapilAsdhir say, but I would add a bit about what you see after you press the power button on a desktop, when you press the power button turns the fan source, power supply to the motherboard and drive two major components to load up the operating system. Hard load the OS in C drive after a time, we have the background is the familiar windows environment which I use often.