Re: Why do CPUs run hotter...?

mc wrote:
Why does a Pentium CPU run hotter when "working hard" (executing complex software) than when the OS is idling?

It is always executing *some* instruction, and in that sense, is never idle.

I understand that CMOS gates dissipate power only when changing state. I *presume* what's going on is that when the CPU is executing software, it is executing a greater variety of machine instructions and therefore heating up a larger proportion of the circuitry in the chip (since there is special circuitry for each kind of instruction).

Am I on the right track? This is one of those dumb questions where I'd like to know the exact answer, rather than just guessing.


If you have the possibility compare the heating of CPU under different OS's, running comparable activities, I noticed it years ago when started using Linux which IS a Unix clone and as such multiuser/multitasking system.
As it has to accomodate "users" by switching between various applications it uses the "halt" command inherent in CPU's which IS not used by MS-Glassware systems although the NT series supposedly are Unix based.
So there IS a diff in heating of the system just depended how it is managed.

Have fun.

Stanislaw
Slack user from Ulladulla.

.

Relevant Pages

  • Re: Cross-Modifying Code
    ... > There's an explicit warning that instruction fetch and page table accesses ... > don't honour xFENCE for prefetched code either. ... > then you don't know when to issue the CPUID. ... The Opteron manuals don't comment on the interaction between executing code ...
    (comp.lang.asm.x86)
  • Re: unset($this) or maybe unset(&$this)
    ... which does not involve a jump is executed the next instruction to be executed will be the very next instruction in the same object method. ... The code may still exist in the class definition, but the object, which contains a copy of that code in memory, does not, so how can it continue executing any of that code? ... When you call something like obj.Func; in C++ (assuming obj is an instance of class Foo), the compiler actually translates that to something like: ...
    (comp.lang.php)
  • Re: Question about Instruction Format (ModR/M)
    ... (the first three bytes, being prefixes, could be in any order) ... This is a 32-bit PM instruction executing in 16-bit RM/PM due to ... they have to push the extra byte back onto the disassembly stream. ...
    (alt.lang.asm)
  • Re: Accessing program counter registers from within C or Assembler.
    ... >> current executing instruction in C while the ... it is close to the second scenario ("Where in memory ... is there a method to load a program image ...
    (Linux-Kernel)
  • Re: IF NOTs
    ... a" will will slower than "FALSE a". ... case (executing x) would be slower than the "TRUE b" case (also ... conditional jump instruction. ... zero as needed. ...
    (comp.lang.forth)
Loading