Nowadays, portable devices such as laptop and notebook computers are very popular.
These devices require energy efficient design in order to maximize battery lifetime. Reducing the
power consumption of microprocessors has become increasingly important. Many studies have
shown that memory accesses account for a noticeably large percentage of the total power
consumption in microprocessors, making the power consumption of caches and main memory an
important concern .
Caches are a significant part of the processor due to the increasing disparity between
processor cycle time and memory access time. High performance microprocessors normally have
one or two levels of on-chip cache in order to reduce the off-chip traffic as much as possible.
Off-chip accesses are not only at least a magnitude slower but also dissipate a large amount of
power via highly capacitive I/O pads. Thus, caches are important not only for high performance,
but also for low power to help reduce the amount of off-chip communication.
The power dissipated by the on-chip cache itself is often a significant part of the power
dissipated by the entire microprocessor. For example, in the StrongARM 110 from DEC and the
Power PC from IBM, cache power consumption is either the largest or second largest
power-consuming block . In the StrongARM CPU which has the current best SPECmarks/
watt rating, 43% of total power is dissipated in the on-chip caches . Another example is the