When people talk about 64-bit computing, it's not always clear
what they mean. Most often, they mean some combination of
register width, bus width, or address space. For the purposes of
this article, it means a processor with 64-bit registers and
64-bit addressing. In the late 1980's, as the desktop processing
industry was still struggling to transition to 32-bits, several
companies (among them DEC, IBM, Motorola, and Apple) were
already in the throes of 64-bit development. When the first
64-bit processor was introduced in 1992 for high-end UNIX
servers and workstations, who would have thought of using that
kind of processing power just a dozen years later in cell phones
and laptops? Yet by the end of the 20th century, desktop
applications had tested the computational and memory limits of
32-bit processors, and growth in high-performance consumer
electronics called for increasingly more powerful embedded
processors with ever-constrained power requirements. Early in
the 21st century, the need for impenetrable