Booting the System
Booting the system occurs when the power to a computer is first turned on, or when the power is turned off and then back on again, in order to facilitate the loading of a program, or to clear volatile memory in order to remedy a problem. This is also called a hard boot, or a cold boot.
The term booting derived from the term bootstrapping, which refers to the loading of a program, and from the expression "pulling yourself up by the bootstraps".
Booting is done when a computer is started up or when a malfunction has occurred, causing computer functions to stall. Clearing the volatile memory is a necessary step to restore the normal performance of the computer. Another type of booting, called a soft boot or a reboot, can be done as well. A soft boot is restarting the computer without turning the power off. This can be accomplished by pushing the reset button or by clicking on the appropriate box in the shut down window.
In the sequence of operations that occur during booting, the computer's operating system is implemented. The status of devices is determined. If a device is not found, the next device in the list is tried. If a device does not have the requisite files, then the startup process will be halted. A common example of the latter is the halt to startup that occurs if a floppy disk has been left in a drive. The following error message will be displayed: "Non-system disk or disk error. Replace and strike any key when ready." The software has attempted to boot the computer off of the floppy disk left in the drive. Because the correct system files were not present on the disk, startup could not continue. In this case, the solution is easy--to remove the disk and press a key to continue the startup.
When a computer is booted, a sequence of events is triggered. An automatic execution of a few critical initial programs occurs. These programs are stored into a permanent system called read only memory (ROM)--Basic Input/Output (BIOS) system. As the BIOS software begins to operate, text is displayed. The text describes features such as the amount of memory installed in the computer and the type of hard disk. One of the first tasks performed by BIOS after the boot is to check the setup of a chip called the complementary metal oxide semiconductor (CMOS). The CMOS setup provides information on custom settings that have been user programmed into the computer. Next, the BIOS determines the operational status of a video card, if present. Operation of the video card is controlled by its own, smaller BIOS or by information residing on another ROM elsewhere. Next, the BIOS checks to determine if the computer is being turned on (a hard or cold boot) or a reboot. The types of boots can be discerned by checking the value at memory address 0000:0472. A value of 1234h is indicative of a reboot--anything else is considered a cold boot.
If the boot is a cold boot, the BIOS verifies, by performing a read/write test, all the random access memory (RAM). Also, the ports that accommodate other hardware, such as a keyboard and a mouse, are checked. And, the BIOS also looks for a peripheral component interconnect (PCI) bus, which conveys information quickly and directly to the microprocessor. If a PCI bus is detected, the BIOS checks all the PCI cards. Any errors detected to these hardware components are summarized as a text message.
As the startup of the computer continues, the BIOS displays details about the processor, floppy and hard drives, memory, BIOS revision and date, and the display. When all conditions have been satisfied, the startup process finishes by loading the operating system from the hard drive. The computer is ready for operation.
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