Power Management
Some CPU power limits let the chip run above the long-term average limit (close to TDP) for short periods. Why does this work?
- AChips and coolers have heat capacity, so temperature does not rise instantly and limits can be respected under brief high power
- BUsing power briefly produces no heat
- CTDP indicates a minimum, not an upper limit
Show answer and explanation
Answer: A. Chips and coolers have heat capacity, so temperature does not rise instantly and limits can be respected under brief high power
Heat goes into raising the temperature of the die, heat spreader and heat sink, and reaching steady-state temperature takes seconds to tens of seconds. So for short periods, power above the cooling capacity can be used without hitting the temperature limit. CPUs have a long-term average power limit and a higher short-term limit, speeding up brief tasks such as responding to user input. If the load persists, power falls back to the long-term limit.
- A. Correct. It exploits the thermal time constant.
- B. Power always becomes heat.
- C. TDP is a guideline for cooling design.