Information Technology Reference
In-Depth Information
CHAPTER 1
Introduction
In the 1980s and early 1990s, computer architecture experienced a phase in which quantitative
performance evaluations became the predominant driver for determining how to build effec-
tive, cutting-edge microprocessors and computer systems. While cost, area, and other metrics
remained important as limits to abide by, performance was during this period the main goal for
which designers optimized.
In the mid- to late- 1990s, power began to be an area of concern for architects. It became
clearer that as Moore's Law scaling succeeded in reducing the feature sizes of semiconductor
devices, their areal power density and high processor clock rates would result in microprocessor
designs that were difficult or impossible to cool.
Interestingly, the CMOS power issues that our field currently faces are not the first
instance of power constraints affecting computer systems design. This chapter will first give a
history of power issues in computer systems, then lay out the trends and issues that lie ahead.
1.1 BRIEF HISTORY OF THE “POWER PROBLEM”
Power and cooling concerns are not strictly a twenty-first century issue for computing. In reality,
prior computing eras have also faced power and thermal challenges. For example, the ENIAC
machine built in 1947 dissipated 174 kW (233 horsepower) [ 29 , 59 ]! A March 1949 article in
Popular Mechanics extrapolated from ENIAC's 18 000 vacuum tubes toward a day in the future
where computers might need only 1000 vacuum tubes and therefore presumably drop toward
only 10 kW of power [ 92 ].
Figure 1.1 illustrates a time history of power trends for selected computers from 1950 to
the present. The y -axis of this plot shows areal power density, that is watts per unit surface area.
While very early (vacuum tube) computers were extremely high in power consumption, their
large areas kept power density relatively low. Furthermore, the switch from high-power vacuum
tubes to relatively lower-power bipolar transistors kept power dissipation manageable for some
time. For example, the Intel 4004 microprocessor had, in 1971, similar compute capability as
the multi-ton, room-sized ENIAC computer, and yet dissipated only a handful of watts.
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