64-bit operating system - Computer Definition
An operating system that is designed to work in a computer that processes 64 bits at a time. Most personal computers today are 64-bit, and mobile devices are expected to begin using 64-bit CPUs in the 2014-2015 time frame. A 64-bit operating system will not work in a 32-bit computer, but a 32-bit operating system will run in a 64-bit computer. See 64-bit computing.