In computing, instant-on is the ability to boot nearly instantly, allowing to go online or to use a specific application without waiting for a PC's traditional operating system to launch.
These machines had complete Operating Systems resident in ROM similar to the way in which the BIOS function is conventionally provided on current computer architectures.
The "instant-on" concept as used here results from loading an OS, such as a legacy system DOS, with a small hard drive footprint.
This offers many advantages over a standard modern operating system: However, this comes at the price of having limited local functionality, while focusing on web / cloud services.
In series filament sets, instant-on was accomplished by adding only a silicon diode across the power switch to keep tube filaments lit at 50% power; the diode was placed such that the typical half wave rectifier of the day was reverse-biased.