What happens when your computer starts up and when it shuts down Starting Up What happens when a computer starts? - POST - Power On Self Test Although there are differences in how each computer actually starts, they all share these basic steps. This example is particularly directed towards Dos and Windows (except where noted). The computer performs a test on itself to make sure all components are available and ready. One important part of the first steps is that the registers (the place where data and instructors go in the CPU to be processed) are cleared of any old code. This is the start of the Power-On Self Test or POST test. The CPU then gets a memory address from the ROM which where to find the ROM BIOS in order to continue the check. The CPU now sends signals on its system bus, the main circuit on the mother board to which all components are attached. The clock is checked by the CPU. All computer functions are regulated by this clock, which sends an impulse at a regular interval. It is very much similar to the beating of a bass drum to mark time in music. POST tests the memory chips on the video adapter and loads information from the video adapter’s own BIOS into the system BIOS. Sometimes the BIOS codes from slower CMOS are also loaded into RAM. Newer PCs have additional equipment which also have their own BIOS on their own cards. These items, called plug and play also get loaded into the system BIOS. The CPU now checks to see if a keyboard is attached, if it is working correctly and if any keys are pressed. Many operating systems permit the user to interrupt the POST test to change the computer’s initial or default behaviors (or environmental variables). POST now checks the paths on the bus to the floppy and harddrives (and other devices) to see what storage and peripheral devices are available. Once all the components contribute information to the system BIOS, and all other checks have been performed, if the test indicates a problem, such as a corrupted FAT table, the test will inform you and usually offer a change to fix the problem via a setup screen. If there are no problems, the operating system will display some form of greeting: on a Windows machine, you see a large Microsoft logo. On a Macintosh, you’ll read "Welcome to Macintosh." Command-line systems, such as Unix, may show nothing but a prompt. To start the computer in safe mode You should print these instructions before continuing. They will not be available after you shut your computer down in step 2. Click Start, click Shut Down, and then, in the drop-down list, click Shut down. In the Shut Down Windows dialog box, click Restart, and then click OK. When you see the message Please select the operating system to start, press F8. Use the arrow keys to highlight the appropriate safe mode option, and then press ENTER. 5. If you have a dual-boot or multiple-boot system, choose the installation that you need to access using the arrow keys, and then press ENTER. Notes In safe mode, you have access to only basic files and drivers (mouse, monitor, keyboard, mass storage, base video, default system services, and no network connections). You can choose the Safe Mode with Networking option, which loads all of the above files and drivers and the essential services and drivers to start networking, or you can choose the Safe Mode with Command Prompt option, which is exactly the same as safe mode except that a command prompt is started instead of the graphical user interface. You can also choose Last Known Good Configuration, which starts your computer using the registry information that was saved at the last shutdown. Safe mode helps you diagnose problems. If a symptom does not reappear when you start in safe mode, you can eliminate the default settings and minimum device drivers as possible causes. If a newly added device or a changed driver is causing problems, you can use safe mode to remove the device or reverse the change. There are circumstances where safe mode will not be able to help you, such as when Windows system files that are required to start the system are corrupted or damaged. In this case, the Recovery Console may help you. NUM LOCK must be off before the arrow keys on the numeric keypad will function. 1. 2. 3. 4. Shutting Down What happens when you shut down Shut Down allows you to gracefully shut down Windows by first saving any open files or reminding you to do so, and then deleting any temporary files that have been in use and are no longer needed. The Shut Down option gives you the option to restart your computer, the equivalent of rebooting, either back into Windows or to DOS. You can protect yourself from losing unsaved information by always using Shut Down when leaving Windows and turning off your computer. To turn off the computer Click Start, click Shut Down, and then, in the drop-down list, click Shut down. This action shuts down Windows so that you can safely turn off the computer power. Many computers turn the power off automatically. To restart your computer Click Start, and then click Shut Down. In the What do you want the computer to do drop-down list, click Restart. As a last resort Hit Ctrl-Alt-Delete. The Task Manager should come up. Try closing down any open/stalled programs by hitting End Task (and End Task again if the window comes up), and then Shut Down again. If that doesn't work, hit Ctrl-Alt-Delete several times until the computer reboots. As a final resort, hold the power button on the computer in until the computer shuts off. Should you leave your computer on all the time? According to TechTV, while it doesn't hurt to leave it on, there's no compelling reason to leave it on all the time. Click the link above to read the full article.