Power Management
In today's chips, which statement comparing the energy of moving data and computing is generally correct?
- AReading data from external DRAM costs tens to hundreds of times the energy of one operation, so reusing data locally saves energy
- BMoving data costs no energy; only computation does
- COne operation costs hundreds of times more energy than a DRAM read
Show answer and explanation
Answer: A. Reading data from external DRAM costs tens to hundreds of times the energy of one operation, so reusing data locally saves energy
Compared with computation over short wires inside an arithmetic unit, moving data off chip to DRAM through long wires and pins costs far more energy. Even on chip, nearby registers cost less energy than distant caches. So keeping data in nearby storage for reuse, reducing data volume (with lower precision) and computing near the data are major ways to save energy.
- A. Correct. Caches and locality help power too.
- B. Data movement consumes a lot of energy.
- C. It is the other way around.