Starting a Computer
The process of starting or restarting a computer is called booting. When turning on a computer that has been powered off completely, you are performing a cold boot. A warm boot, by contrast, is the process of using the operating system to restart a computer. A warm boot properly closes any running processes and programs; however, it does not save any unsaved work. Thus, always remember to save your work before rebooting (restarting) a computer. Warm Boot versus Cold Boot
With Windows, you can perform a warm boot by clicking the Start button on the taskbar, clicking the arrow next to the Shut down button on the Start menu, and then clicking Restart. When you install new software or update existing software, often an on-screen prompt instructs you to restart the computer. In this case, a warm boot is appropriate. If the computer stops responding, try pressing and holding down the power button to turn off the computer. A standard power button is shown in xx.
Figure : Power Button
As a last resort, remove power from the computer and then restart the computer. On newer computers, pressing the power button momentarily is the same as a warm boot, whereas pressing and holding the power button does not properly close running processes and programs. The Boot Process
Each time you boot a computer, the kernel and other frequently used operating system instructions are loaded, or copied, from storage into the computer’s memory (RAM). The kernel is the core of an operating system that manages memory and devices, maintains the computer’s clock, starts programs, and assigns the computer’s resources, such as devices, programs, data, and information. The kernel is memory resident, which means it remains in memory while the computer is running. Other parts of the operating system are nonresident, that is, these instructions remain on a storage medium until they are needed. The boot process is similar for large and small computers. The steps in the following list explain what occurs during a cold boot on a personal computer using the Windows operating system.
1. When you turn on the computer, the power supply sends an electrical signal to the components in the system unit.
2. The charge of electricity causes the processor chip to reset itself and find the ROM chip(s) that contains the BIOS. The BIOS (pronounced BYE-ose), which stands for basic input/output system, is firmware that contains the computer’s startup instructions.
3. The BIOS executes a series of tests to make sure the computer hardware is connected properly and operating correctly. The tests, collectively called the power-on self test (POST), check the various system components including the buses, system clock, adapter cards, RAM chips, mouse, keyboard, and drives. The POST results are compared with data in a CMOS chip. The CMOS chip stores configuration information about the computer, such as the amount of memory; type of disk drives, keyboard, and monitor; the current date and time; and other startup information. It also detects any new devices connected to the computer. If any problems are identified, the computer may beep, display error messages, or cease operating — depending on the severity of the problem.
4. If the POST completes successfully, the BIOS searches for specific operating system files called system files.
The BIOS may look first to see if a USB flash drive plugged in a USB port or a disc in an optical disc drive contains the system files, or it may look directly on drive C (the designation usually given to the first hard disk) for the system files.
5. Once located, the system files load into memory (RAM) from storage (usually the hard disk) and execute. Next, the kernel of the operating system loads into memory. Then, the operating system in memory takes control of the computer.
6. The operating system loads system configuration information. In the latest Windows versions, the registry consists of several files that contain the system configuration information. Necessary operating system files are loaded into memory. On some computers, the operating system verifies that the person attempting to use the computer is a legitimate user. Finally, the Windows desktop and icons are displayed on the screen. The operating system executes programs in the Startup folder, which contains a list of programs that open automatically when you boot the computer. Boot Disk
A boot drive is the drive from which your personal computer boots (starts).
In most cases, drive C (the hard disk) is the boot drive. A computer’s hard disk typically is enclosed in an airtight sealed case to protect it from contamination. xx shows a standard hard disk.
Figure : Hard Disk
Sometimes a hard disk becomes damaged and the computer cannot boot from the hard disk. In this case, you can boot from a special disk, called a boot disk or a recovery disk, that contains a few system files that will start the computer. When you purchase a computer, it usually includes a boot disk in the form of an optical disc. If you do not have a boot disk, the operating system may provide a means to create one. Shutting Down a Computer
Although some users leave their computers running continually and never turn them off, others choose to shut them down. If you shut down a computer, it is important to do it properly; you never should simply turn the computer off. Shut Down Options
Shut down options include powering off the computer, placing the computer in sleep mode, and hibernating the computer. Sleep mode saves any open documents and programs to ram, turns off all unneeded functions, and then places the computer in a low-power state. If, for some reason, power is removed from a computer that is in sleep mode, any unsaved work could be lost. The hibernate option, by contrast, saves any open documents and programs to a hard disk before removing power from the computer. You can obtain help if you are unsure which options to use. xx shows the Windows Help and Support Center information for shutting down a computer properly.