Dear Not_a_short:
TDP means thermal dissipation power and yes, I am using it as a shorthand for thermal output like many on this thread. It has the same acronym as TDP, thermal design power, commonly used by Intel. It is used as a marketing dodge by Intel. Thermal dissipation power is how its historically perceived and how Intel used to specify their CPUs in the old days. We have had a lot of debates revolve around the difference in these two definitions. Intel's TDP was defined like typical power was used in the past and AMD defined it more like maximum possible thermal dissipation power for a family of CPUs, a bounded power constraint never to be exceeded. Thus TDP(intel) < TDP(AMD) which I shortened to TDPtyp and TDPmax. You can find both powers at a place like www.sandpile.org. Intel supporters hated the fact that when using the same historical standards, their CPUs had a higher TDPmax than their design power rating. So their 80W design power 3GHz@1333MHz FSB C2D actually carries a TDPmax of 124.83W. That is higher than the TDPmax of 119.2W of the 3GHz Opteron 8222SE. TDPs as specified by AMD are all absolute upper bounds on actual dissipation of any given CPU. Many CPUs may be much lower than the amounts specified.
TDP does change depending on the conditions used. There is a TDP for each power state. On my 90nm SC A64 3500+ (Venus), there are 4 P (power) states, 2.2Ghz, 2.0GHz, 1.8GHz and 1GHz each with its own required voltage defined by the VID. In addition there are sleep states. Mobile chips have more sleep states than desktop or server chips. These have various circuits or voltage planes turned off or idle. One used is S1 IIRC where the CPU is halted in a stop grant state, the HTT ports, NB and DDR controllers are still active. It can be done at every P state having a TDP for each. Of course the lowest on mine would be P4S1, 1Ghz. There is sleep state S3 where the CPU is turned off having saved its state to DRAM, the HTT ports are off and the DDR memory is turned to self refresh. On mine, it is constrained to not use more than 350mW.
My series of A64s had variable TDP specified as each chip had its own max TDP. Where the family allowed up to 68W, my CPU had a TDPmax of 50W. Some had one as low as 35W.
And thermal output does vary with time. Most of the time it gets worse as time goes on, but occasionally it gets better. Mine is in the latter group.
Pete |
