System Rest

System Rest was the ability of classic Mac OS to slow down a processor from its normal speed to reduce power consumption and extend battery life.

History
System Rest was introduced in System 6.0.4 as an exclusive feature of the Macintosh Portable, which was released on September 20, 1989. If enabled, it would slow down the Motorola 68HC000 processor from 16 MHz to 1 MHz when idle and no user input has been detected for 15 seconds. The System Rest feature is comparable to the Doze Mode of modern processors.