| 1. Booting Up | | | | stored in the BIOS to start the operating system. It |
| It is useful to understand what happens behind the | | | | will start by reading from the first bootup device. If it |
| scenes when you switch on your computer from a | | | | points to the floppy drive, it then searches for a |
| cold idle machine to an operable and functional | | | | floppy disk. If it does not detect a bootable diskette |
| system. There are essentially two forms of booting - | | | | in the floppy drive, the system displays an error |
| the soft boot and the hard boot. | | | | message. |
| The warm boot or hard boot involves powering the | | | | If the floppy drive does not contain a diskette, it |
| computer up from an initial zero power supply. | | | | bypasses the first bootup device and detects the |
| A cold boot on the other hand takes place when a | | | | second device, which is usually the hard disk. It'll then |
| software application or operating system triggers the | | | | start by reading the boot code instructions located in |
| computer to perform a reboot. | | | | the master boot record and copies all execution into |
| A successful boot is dependent on 3 conditions - the | | | | the memory when the instructions are validated and |
| hardware, BIOS and operating system files to | | | | no errors are found.c. Boot Loader Phase |
| function without errors. When an error occurs, you | | | | Control is then passed on to the partition loader code |
| will be notified by error messages, beeping sounds or | | | | which accesses the partition table to identify the |
| in the worst scenario, a blank screen. | | | | primary partition, extended partitions and active |
| 2. Bootup Process | | | | partition which is needed to determine the file |
| The bootup process is a list of detailed procedures | | | | system and locate the operating system loader file - |
| that the system undergoes to perform all system | | | | NTLDR. NTLDR will then switch the processor from |
| checks and load all necessary files to bring the | | | | real-mode to 32 bit protected mode which memory |
| computer to an operable state. | | | | paging is enabled. |
| The Windows XP bootup process comprises of the | | | | NTLDR will call upon the boot.ini file which is located |
| following procedures:a. The Power-On Self Test | | | | at the root directory to determine the location and |
| Phase | | | | entries of the operating system boot partition. At |
| As soon as you power up your computer, a self-test | | | | this point in time, the bootup menu is displayed on |
| is performed by the power supply to ensure that the | | | | the screen to allow you to select an operating |
| volume and current levels are correct before the | | | | system to start from if you have more than 2 |
| Power Good signal is sent to the processor. When | | | | operating systems installed in your computer. |
| this first stage is cleared, the microprocessor will then | | | | NTLDR will pass all information from the Windows |
| trigger the BIOS to perform a series of operations.b. | | | | registry and Boot.ini file into Ntoskrnl.exe.d. Operating |
| BIOS ROM Phase | | | | System Configuration Phase |
| The BIOS, also known as the Basic Input Output | | | | Ntoskrnl will begin to load the XP kernel, hardware |
| System is a firmware or set of instructions that | | | | abstraction layer and registry information. |
| resides on a ROM chip as contained in the | | | | After this is completed, the control is passed over to |
| motherboard. | | | | the DOS based program which collects and |
| It first carries out the P.O.S.T that performs and | | | | configures all installed hardware devices such as the |
| verifies all initial hardware checks, such as checking if | | | | video adapters and communication ports. |
| the system is initialized by a warm or cold start, | | | | then searches for hardware profiles information and |
| detecting the presence of peripheral devices and the | | | | load the essential software drivers to control the |
| amount of memory present. | | | | hardware devices.e. Security & Logon Phase |
| It then accesses the information stored in the CMOS | | | | Lastly, Ntoskrnl.exe will start up Winlogon.exe which |
| chip, DIP switches, jumpers and assigns the | | | | triggers the Lsass.exe or Local Security |
| necessary system resources. After this, the | | | | Administration which is the logon dialog interface that |
| hardware' firmware will individually carry out its own | | | | prompts you to select your user profile and verifies |
| diagnostic test such as S.M.A.R.T. | | | | your necessary credentials before you are |
| The system will now attempt to determine the | | | | transferred to the Windows desktop. |
| sequence of devices to load based on the settings | | | | |