BOOTING in WINDOWS XP BY Justin Metzger
Power Good • Power Good is the signal sent to the processor from the power supply • It is sent once the voltages ad current levels are acceptable • This process takes anywhere form .1 to .5 seconds • Upon arrival of Power Good, the Timer Chip stops sending reset signals so the CPU can start operations
ROM BIOS code • The CPU starts executing the ROM BIOS code • The CPU loads the ROM BIOS starting at ROM memory address FFFF:0000 which is only 16 bytes from the top of ROM memory • The ROM BIOS does a test of central hardware to verify basic functionality • Any errors that happen now will be reported by means of ‘beep-codes’
Cold Start or Warm Start • To determine whether this is a warm start or a cold start the ROM BIOS startup routines check the value of 2 bytes located at memory location 0000:0472 • Any other value other than 1234h indicates that this is a cold start • If this is a cold start the ROM BIOS executes a full POST • If this test is a warm start the memory test portion of the POST is switched off.
Difference between cold and warm start • Cold boot (cold start) is starting the computer after it has been powered down for a while • Warm boot (warm start) is restarting a computer that has already been turned on • For example in hibernating mode
What is POST? • POST is broken down into 3 components which are the following: • The video test initializes the video adapter, tests the video card and video memory, and displays configuration information or any errors • The BIOS identification displays the BIOS version, manufacturer, and date • The Memory Test tests the memory chips and displays a running sum of installed memory
CMOS • CMOS stands for Complimentary Metal Oxide Semiconductor • The BIOS locates and reads the configuration information stored in CMOS • CMOS is maintained by the current of a small battery attached to the motherboard • CMOS is a small area of memory containing 64 Bytes • Most importantly for the ROM BIOS startup routines CMOS indicates the order in which drives should be examined for an operating system-floppy, CD ROM, or fixed disk
Finally Logging on • The Window XP booting process is not complete until a user has logged on • The process is begun by the WINLOGON.EXE file • Which is loaded as a service by the kernel and continued by the Local Security Authority, which displays the logon dialog box • The logon dialog box appears at approximately the time that the Services Subsystem starts the network service