instant on
n. A feature that enables a computer or similar device to be ready for use as soon as it is turned on.
instant-on adj.

Example Citations:
Then [Microsoft], based in Redmond, Wash., plans “sometime in 2000” to release a new consumer version of Windows that will offer an as-yet-unannounced set of easy-to-use consumer features, such as “instant on.”
—John Markoff, “Behind the Big Shift on Windows,” The New York Times, April 9, 1999

But why are experts so bullish about a Windows-CE hegemony? First, it is not a hefty OS. It is simple to use-with one hand operation, instant on/off interfaces and the familiar Windows icons.
—Kavita Kaur, “Windows CE Operating System: Win Hands Down,” Computers Today, February 1, 1999

Earliest Citation:
The companies were helped along by manufacturers of consumer appliances. Homes of the ‘60s and ‘70s filled up with hair dryers, coffee makers, microwave ovens, instant-on TVs...
—Stephen Petranek, “The Power Brokers,” The Washington Post, August 26, 1979

Related Word: