The button for turning an electrical device on and off has a simple interaction familiar to anyone who has ever used a flashlight or a television: pressing the on/off button turns on the equipment when it is off; pressing the same button turns off the equipment when it is on. In fact, most electrical equipment works this way. To the detriment of usability, computers are a notable exception.
Before a computer can shut down, the operating system needs to perform housekeeping tasks such as storing settings and unsaved data, and powering down hard disk drives and optical media devices. To ensure that the operating system can perform these tasks, the operating system requires us to select a Shut Down option from a menu. However, this requirement breaks the mental model we have for operating electrical equipment: the action for turning off a computer—selecting a menu option—is inconsistent with the action for turning on the computer—pushing the on button. These actions are not only inconsistent within the computer system, they are inconsistent with most other electrical devices. When we turn on a computer, we press the on button. Why can’t we press the same button to turn off the computer, like we do with the other electrical equipment in our homes and offices?
Ideally, that is exactly what should happen. The same button should turn off the computer that was used to turn on the computer. Pressing the on/off button should initiate the shut-down procedure rather than the selection of the Shut Down menu option. The problem with implementing this interaction style lies in the difference between the two types of on/off buttons in common use. The first type is a physical toggle button: pushing the button in connects the computer’s circuits to the power; pushing the button again disconnects the computer’s circuits from the power. This type of toggle button doesn’t give the operating system the chance to perform its housekeeping, which is why Windows, for example, often blames the user for not shutting the computer down correctly the next time the user switches it on.
The second type of on/off button is a logical button that issues a command to the equipment. For example, the front control panel of a DVD player uses logical buttons to play and stop the DVD and to eject the DVD tray. The same DVD player also uses a logical button to put itself into standby mode. Although standby mode is not truly off because the power is still connected, the graceful way in which well-designed DVD players handle their housekeeping tasks is an interaction model computers should follow. For example, if the DVD tray is open when the player is put into standby mode, the player closes the tray before going into standby.
To turn off a desktop computer with the same toggle button used to turn it on, the computer would need a battery large enough to power the computer while the operating system performs the shut down process. Adding a battery to desktop computers would also enable them to shut down gracefully after a power cut or when the power cord is unplugged from the wall socket. Laptops already gracefully revert to battery power when the AC adapter is unplugged so laptops would need less re-engineering to incorporate an humane on/off switch.
Humane on/off switches—ones that operate predictably based on experience with other electrical equipment—would also make computers seem friendlier and easier to use: predictable outcomes comfort novices and smooth the interaction for everyone else.