Why are CPU temperature changes rapid and GPU slower?

[Confused Stu]

This is one of those "I've always wondered but never got round to asking" questions. Temperature changes recorded on CPUs are very rapid - start Prime95 and your CPU goes from 20C to 90C in a second and stay there, and dropping temperatures are just as quick. Temperature changes recorded on GPUs are a lot slower, so start up a game and your GPU will slowly climb until it plateaus on its maximum temperature after a few minutes, then takes best part of a minute to cool back down.

Is this because the temperature sensors are in different positions - with the CPU sensor being close to the action and the GPU sensor being more in a heatsink rather than the core? This doesn't seem likely as removing the cooler on most GPUs reveals the bare core rather than an integrated heatsink like a CPU comes with. Is it due to the different construction of the chips, with the CPU being an individual made up of 2/4/6 or 8 "bits" where the GPU is made of thousands?

Or is it something completely different that I've been a spoon for never realising?

 

[forteh]

Consider the relative size if the heatsink between the cpu and gpu; the cpu is invariably much bigger with more space around it to dissipate heat, the gpu has a more compact and far less efficient cooler.

I replaced the heatsink on my gtx660 with a thermalright hr03gtx ( redrilled the mounting hardware to make it fit) and use a 140mm case fan to direct cold air directly onto it, my gpu temperature drops just as quick as cpu when the load comes off.

Generally gpu coolers require the air passing through the heatsink to immediately turn through 90° in order to exit, it doesn't like doing this so won't efficiently carry the heat away

edit: not to mention that the hr03 dropped the load temps by almost 40℃

 

[P4Clock]

Gpu's run a lot hotter then CPU's. a stock intel heat sink on an mid range gpu would result on overheat shout downs in a few mins where it can keep the cpu cool for hr's of gaming.