Every time you turn on your computer, the machine and Windows XP perform a series of actions, always in the same order: First, the read-only memory basic input/output system (ROM BIOS) performs a series of diagnostic tests to confirm that the processor and memory are working properly. Then it tests some of the computer’s other components, including the hard drive and the video display. When those tests are complete, the BIOS runs the first of a series of programs that lead to starting the full Windows operating system. In other words, the whole startup process uses a relatively simple program located on a memory chip to start other, more complex software in several stages.
Power-on Self Test (POST)
The power-on self test (POST) is the first thing that happens when you turn on the computer. During the POST, the central processor uses instructions in the BIOS firmware (software located in a memory chip on the computer’s motherboard) to confirm that the power supply is working properly, run some memory and hardware tests, find operating system software on a hard drive or some other storage media, and set the configuration options specified in the BIOS.
When the computer detects a problem during the POST, it either displays a text message that describes the error, or it sounds a series of beeps (actually, beep codes). If the problem is so serious that it will not allow the computer to work properly (such as a massive memory failure), the system will either lock up or turn off the computer completely.
Some of these error messages halt the POST, so the message remains visible on your monitor screen, but others might scroll past before you can read them. To stop the text from disappearing, press the PAUSE BREAK key on the right of the normal keyboard. To resume the startup routine, hold down the CTRL key and press PAUSE BREAK again.
Beep Codes
If the POST detects a memory problem or some other condition that keeps the video display from showing error messages, a beep code will sound within the first 30 seconds after you turn on the computer. If you hear a beep code, note the number of long and short beeps and the order in
which they sound. See Appendix A for a list of common beep codes. Each type of BIOS uses a distinct beep code pattern, so it’s relatively easy to identify the problem that produced the code, even if you don’t know the brand of BIOS your computer is using.For example, if you hear one long beep followed by three short beeps, the computer has an AwardBIOS, and the POST has detected a memory problem; a 1-2-2-1 code (one beep, pause, two beeps, pause, two beeps, pause, one beep) indicates a keyboard problem on a PhoenixBIOS.
Some computer motherboards also display POST codes on an LED readout mounted on the board. You’ll have to remove the cover from the computer case to see this display. If your computer has such a display, you can find a list of codes in the manual or on the motherboard maker’s website.
Some computer motherboards also display POST codes on an LED readout mounted on the board. You’ll have to remove the cover from the computer case to see this display. If your computer has such a display, you can find a list of codes in the manual or on the motherboard maker’s websi
Initial Startup: What Happens When You Push the Button After the computer completes the POST built into the motherboard, it ma run additional tests on some of the other components, including the hard drive and the video adapter. Each of these tests can produce its own set of
error messages.
When the POST is complete, the computer tries to load the operating system software stored on the hard drive (in this case, Windows XP), a floppydisk, a CD, or some other storage device.
A problem can occur during initial startup for several reasons:
If the BIOS does not discover any problems, it locates the boot sector on the startup drive and runs a Windows boot loader program called ntldr (NT Loader or boot loader). Ntldr takes over control of the computer from the BIOS. (The filename ntldr is left over from the earlier version of Windows called Windows NT; hey, whatever works.)
Run the Boot Loader
The boot loader program loads a series of startup programs, instructs the central processor to handle 32 data bits at one time, and starts the file system that Windows will use to exchange data with the hard drive.
Finally, the boot loader reads the boot.ini file that identifies the location of the operating system files and runs the ntdetect.com program to detect and configure the hardware connected to your computer.
Detect and Configure Hardware
Windows uses the information gathered by ntdetect.com to identify and configure the various hardware devices that it uses to send, receive, and store data. This includes the keyboard and mouse; disk drives and other data storage devices; the video adapter that controls the monitor display; the I/O (input and output) ports, including the serial, parallel, Ethernet, and USB
ports; and any other input or output devices installed in the expansion slots on the motherboard. Ntdectect.com also reads certain information from the BIOS firmware, including the time and date.
Load the Windows Kernel
The file ntoskrnl.exe in your Windows installation is the Windows kernel; itcontains the core of the Windows XP operating system. The ntldr program loads the kernel into memory, along with a file that contains information about the specific hardware installed on this computer. Once these two file(ntoskrnl.exe and the hardware file) load successfully, Windows starts a series of programs called the “Windows executive” that reads configuration information from the Windows Registry and starts the secondary programs and background services that have been set to load during startup.
Once the kernel finishes running the startup instructions in the Registry it runs the Session Manager program (smss.exe), which, among several other important functions, shifts Windows from text mode to graphics mode. In other words, this is the point at which you begin to see graphic images on your screen.
Logon
At this point, Windows XP is in control of your computer. The logon routine requests the current user’s username and password (if any). Once that user logs in, Windows loads any additional startup programs specified in the Registry for that user’s account.
