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I'm using this Windows XP computer at work right now and I realized it's poor performance may be due to it only using one core, details follows:

  • Processor is a Pentium E5400
  • The multi-core feature is enabled in BIOS
  • Device Manager shows both cores under "Processors"
  • Intel Processor Identification Utility shows both cores
  • CPU-Z only detects one core
  • Task Manager's performance tab only shows one graph ("One graph per CPU" option is enabled).
  • While doing heavy operations CPU goes to 100%, I would expect it to go to 50%
  • Process Explorer (by sysinternals) also shows only one graph.
  • msconfig has no option checked under "BOOT.INI"->"Advanced options" (and if I try to check /NUMPROC I only have the "1" option)

I'm puzzled, it looks like the second core is detected as hardware but it's not being used. Any help?

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Have you tried putting in another hdd, installing Windows XP, and verifying what it shows? – Ramhound Nov 29 '12 at 15:20
That's my company's pc at work, sadly I'm not allowed to play that much with it (actually I'm surprised I'm allowed to install application and access the BIOS). I take from your answer that you suggest something went wrong with the OS installation, right? – capitano666 Nov 29 '12 at 15:35
I'll post a comment rather than an answer, as not sure it will work in your case. See If your XP installation was ghosted from a single CPU machine (as can happen in corporate environments) you might need to enable multi-core support. – DaveP Nov 29 '12 at 15:49

I have seen this happen with working with VM's and XP. Have you ever replaced the CPU of this computer from a single core CPU to a dual core CPU?

The easiest solution for this when I encountered this with a VM where I added an additional core is doing a "Repair Install" of XP and it will refresh the internals of XP to use all of the available cores.

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