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