1 amp when entire 'system' is working hard and 0.55 amps
when only CPU (no peripherals) is doing work. Those numbers
can be interpreted this way as well. However, take the
heatsink off that CPU when 'system' is only consuming 0.55
amps. Will processor still work 'not hard'? Heatsink cannot
be removed because CPU is working hard at both 1 amp 'system'
consumption and 0.55 amp 'system' consumption. So hard that
heat sink is required during both events. Running at 0.55
amps or sprinting at 1 amp system consumption.
Where may the first 0.55 amps be going? Mostly to CPU when
'system' is doing less.
An overheating Pentium activates an internal emergency
protection circuit that was even found in 486s. No mystery
there. To protect a CPU that is overheating, then CPU cycle
execution time is slowed (in some Pentiums is said to stop).
This is not 'normal computer' operation from a user's
perspective (probably why it is not discussed in datasheets).
>From a user's perspective, is CPU 'not working hard' when user
does not execute application programs? No. CPU is 'working
hard' constantly which is why CPU always needs that heatsink.
CPU is always doing something on every clock cycle.
Sometimes that may only be a Halt instruction (reduced
power). After all, how does it know when to stop executing
Halt? Its reduced processing detects the interrupt. Other
times, CPU is executing those other 20+ processes. All this
is still so 'hard' that CPU requires heatsink even when not
executing anything for the user.
Fan tells us little about how much more heat a Pentium
produces. It simply reports when the CPU is 'running' verses
'sprinting'. Again, take the heatsink off any processor that
is 'not doing anything'. See how long it can still 'do
nothing' - normally. Why? Because even when it is 'not doing
anything', it is doing so much as to generate heat that
requires a heatsink.
And so we return to the question. What, from the user's
perspective constitutes hard work? Electrical consumption /
thermal dissipation, or output from CPU to be observed by
user? CPU electronics can still execute and yet not provide
the user with any useful output. Is user then to assume the
CPU is doing almost nothing? If so, they why is CPU still
producing so much heat?
Again, the question - does a laptop tend to execute more
Halt instructions as compared to a desktop?
Paul wrote:
> I was hoping that my quotation of the power figures on my new
> computer would make that apparent. 1 amp when "working hard"
> and 0.55 amps when not "working hard". You see, I am one of
> those "laymen" who chooses to believe that when a peocessor
> executes a HLT instruction, the processor "stops working hard".
> It is sleeping. It will be awakened by the next hardware interrupt,
> and when that happens, the power consumption will climb.
>
> The power consumption is not constant, neither is the rate that
> work is being done. There are a number of throttling mechanisms
> at work. An example we haven't talked about yet, is how the
> Pentium behaves when it overheats. It doesn't execute an instruction
> on every clock tick. It has some clock cycles where it does nothing,
> in an attempt to reduce the processor temperature to a safe point.
> This is why it is possible to execute Prime95 on a Pentium4 and
> rip the heatsink/fan off the processor while it is running. Even
> though the Prime95 program wants to use every cycle, the throttling
> feature inside the processor reduces the percentage of clock cycles
> during which instructions are executed. This reduces the processing
> rate and the heat dissipated. (No, I haven't read any Intel docs on
> this, so I don't have any links to quote from. This is paraphasing
> what I've read in this newsgroup.)
>
> With the temperature controlled fans in the system, I don't need
> to look at a "process viewer" to tell when the CPU is running
> at 100%. The fans tell me when the CPU is really busy, as they
> make an awful lot of noise when the CPU and PSU heat up.
>
> What I'm objecting to is the notion that the CPU executes an
> instruction on every clock cycle. For some periods of time, the
> processor is asleep. For some percentage of clock cycles during
> periods of overheat, the processor will not execute an instruction,
> in an attempt to reduce the temperature. So, while in times past,
> a processor used to execute an instruction per clock cycle (no
> power reduction features in those processors), current processors
> have a whole array of features that give variable performance.
>
> Even the Northbridge has a throttling feature. Many Northbridge
> chips have a % duty cycle counter in them, which watches how ofter
> a DIMM is accessed in a given interval. If the duty cycle is too
> high, the Northbridge will actually reduce the rate that it does
> transactions on the DIMM. And if the memory stops responding, this
> causes the processor to stall (which causes its power dissipation
> to drop as well). This feature has to be supported in software, and
> I don't know if modern OS enable it or not. Here is an example
> in the 845PE datasheet:
>
> http://developer.intel.com/design/chipsets/datashts/25192401.pdf (pg.98)
>
> Paul
Received on Sat Dec 13 2003 - 20:05:34 PST