Handheld gaming devices are usually compared on their processors. The more binding constraint is heat, and it limits performance long before the silicon does.
Surface temperature is a hard ceiling
A device held continuously cannot get uncomfortably warm where hands rest. That sets a maximum surface temperature independent of what the internal components could tolerate.
Heat must therefore leave through a small area, at a modest temperature difference, into air that the user is also sitting in.
Everything else in the thermal design exists to work within that ceiling. It is not an engineering preference but an ergonomic requirement.
Sustained power is the number that matters
A processor can run at high power briefly by absorbing heat into its own mass and the surrounding metal. That reserve is measured in seconds to minutes.
Once it is used, the device settles at whatever power its cooling can remove continuously. Long sessions run at that sustained figure, not the peak.
This is why brief benchmarks flatter handhelds. The interesting measurement is performance after the thermal system has reached equilibrium.
Fans trade noise for headroom
Active cooling raises sustained power, but fan noise in a device held near the face is intrusive in a way it is not in a desktop.
Designers therefore tune fan curves conservatively and accept lower sustained power rather than a device that sounds strained during quiet gameplay.
Small fans also move air inefficiently. Halving the diameter costs far more than half the airflow, which is why handheld cooling is disproportionately hard.
The battery competes for the same space
Battery cells dislike heat, and heat accelerates their capacity loss. Placing a large cell next to a hot processor shortens the device's usable life.
Separating them consumes internal volume, so a bigger heat spreader means a smaller battery and a smaller battery means shorter sessions.
Every handheld resolves this trade differently, which is why devices with similar processors can differ substantially in both runtime and sustained performance.
Software has become part of the thermal system
Power limits are now dynamic, with the system shifting budget between processor and graphics based on what the current scene demands.
Frame rate caps and resolution scaling reduce heat generation directly, which is why a locked lower frame rate can feel steadier than an uncapped higher one.
Upscaling helps for the same reason: rendering fewer pixels lowers power draw, and lower power draw is what keeps the sustained clock from falling.