I don't know why, but every time I switch off my computer after reading this message, I just get images in my mind of the whole thing exploding in my face.

Then, sitting with blackened face and slightly burning hair in the remaining shell of my bedroom, I say; "Welp. That was ironic." *

Sometimes the images are worse than the voices. oh, for just one moment away from the voices...

* and then Alanis Morrissette appears in the corner with sixty billion forks and a can of soup. she's crying.

It is inherently unsafe to shut down a computer in the middle of what it is doing, whatever it is. For the most part, this is due largely to the physical hard disk and what state the information transfer is in when the power goes down. This message is commonly associated with the Windows operating system, even though Linux and Macintosh also need to shut down properly to keep up health. If you are seeing this screen under Windows, you do not have a "Power Smart" motherboard (typically all ATX configurations are), as the computer releases the power through a command to the board. Instead you will need to manually disengage the power.

In a generic sense Windows and Linux need to accomplish these tasks in this order to shut down Many OS's perform a disk check after power is lost, or an unexpected shutdown occurs, this is to verify disk block integrity. There is no telling where the head of the disk could have been when it performed it's last action, or what it wrote to, or how far it got before it died. It's all at the mercy of entropy, and thus most modern systems use a disk checking utility if it senses that a disk was not unmounted cleanly. For Windows NT there is chkdsk, Windows 9x has scandisk/ scandskw, there is Macintosh Disk First Aid, and Linux has fsck. Though this is burdensome and oftentimes yields nothing, it is the disk errors that pile up that can cause a great amount of lost data and general instability.

The concept of disk checking on Windows-based fat16 systems was originally put together by Peter Norton, the Norton Utilities guy in the form of chkdsk 4.0 for DOS. (Unix had disk checking on their filesystems long before Windows.) Scandisk saw the light of day with DOS 5.0 with the advent of Smartdisk, disk caching software responsible for many lost clusters. The Norton trademark was eventually purchased by Symantec, who created what went on to become Windows Scandisk). Microsoft, after seeing the benefits of regular system maintenance, Scandisk was included with the software diagnostics that went into the original Windows 95, even though Norton kept publishing it's toolkit (with many added features). Microsoft licenced this technology from them, no doubt for quite a sum, seeing the distribution of all of the OS's.

It should be noted that shutting down from single-user mode, or MS-DOS mode (the VGA graphic you see is on some systems just on top of a DOS prompt) is usually fairly safe. There is very little OS to worry about, and there are not usually a lot of daemons and behind-the-scenes items to worry about. This is typically the point of these modes. Windows NT 4.0 brings you to a VGA GUI screen where it says it is safe to shut down. It is only holding the bare minimum of drivers in memory when it does this, and all the disks are unmounted from the kernel.

Another very rare, but possible problem with just slamming the power button off on your machine while it is running is that of a power flash across the board. It isn't likely, but it is possible that the machine lets go of all the juice a little funny, and some of it does some damage to the circuits on the way out. Violently jerking the power on and off to a system is not good for it, and can cause serious damage over time. Many computers that have been mistreated you will find have "flukey" hardware troubles compared to people who maintained their systems.

Doing what your computer thinks is best is almost never a bad thing when it comes to maintenance. My advice to you is to never skip that disk check unless you want to take that chance (or you know it's absolutely wrong). Disk damage on the file system level can and does happen this way everyday. It's best to stay on top of it before it spreads and causes damage elsewhere on your system.

Thanks to bane and frater_219 for corrections and clarifications

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