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Preventing Data Loss and System Problems At Shutdown

Following proper shutdown procedures can eliminate a number of different problems that occasionally plague computer users. In general, simply shutting off the PC when you decide that you are done with it is a very dangerous practice with today's multitasking operating systems. There are two main reasons for this, and both are related to the fact that the system typically has many things going on at the same time:

• Unexpected Activity: Modern operating systems, such as Windows 95 or Windows NT, have many different tasks running on them at the same time. Even when the system appears to be idle, there are various system jobs in operation. These can lie dormant for minutes or hours and then start up unexpectedly and jump into operation very quickly. Examples would include memory-resident virus-scanning programs, screen savers, automatic backup utilities, program schedulers, etc. One of these programs can decide to start up a fraction of a second before you hit the power switch on your seemingly "idle" PC, with the result being that you are cutting the power to the hard disk in the middle of a write operation. This can damage the file system and threaten the safety of the files on your disk.
• Open Files and Caches: Modern operating systems also have files that remain open whenever they are in operation. Further, they use disk caching, which can sometimes mean that writes to the hard disk are held pending in memory, for performance reasons. Turning off the PC before the system has a chance to close its open files and flush the disk cache can lead to data loss and file system corruption.

In general, you should avoid unexpected shutdowns of the PC (unexpected either by yourself, or unexpected by your operating system). To avoid the problems described above, you should always do the following before you try to shut down your PC:

• Save Data in All Open Applications: Make sure you save any files you are working on in all open programs. Most programs will either automatically save for you when you exit them, or at least ask you if you want them to be saved, but watch out for the few braindead applications that will exit without saving unless you are careful.
• Close All Open Applications: Close all programs that you have opened. In Windows, this is most easily done by using the {Alt}+{F4} key combination in each program and responding to prompts. To close an MS-DOS prompt, type "EXIT" at the prompt and hit {Enter}.
• Shut Down the Operating System: Give the proper command to the operating system to shut it down. In Windows this is done using the {Alt}+{F4} combination, or choosing "Shut Down..." from the Start menu. Wait until you are instructed that it is safe before hitting the power switch.

Power failures appear to the system as unexpected shutdowns also, of course. Avoiding power loss is a good way to avoid problems with your system. Using an uninterruptible power supply (UPS) is good protection; also read these power problem protection ideas.

Next: Dealing With a "Hung" PC

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