HOWTO: Get Windows 7 to detect your new multi-core processor

There is a very rare instance that may happen under Windows 7 if you upgrade

your processor from a single to a dual or a dual to a tri or a tri to quad core processor. Under Windows Task manager > Performance tab you may encounter only the previous amount of cores visible even if you have Task Manager > View > CPU history > One Graph per CPU checked off.

This graph pane area which should show the equivalent amount of cores per graph is directly tied into the MSConfig > Boot tab > Advanced options > "Number of Processors" setting. You may not show the correct amount of cores in this MSConfig pull-down.

Let me give an example:

You install Windows 7 with a dual-core processor and have this option checked for "Number of Processors" (in Msconfig > Boot > Advanced options) and the amount set to "2" (for dual core). This setting is not mandatory to be set but some ppl do in order to force Task Manager to show 2 graphs (or 3). One graph for each processor. At a later point in time you upgrade to a Quad-core or Tri-Core processor. The OS will not read this extra core or have anything enabled to physically use this extra core(s) until the following are performed:

1. Uncheck in MSConfig > Boot tab > Advanced Options > "Number of Processors" and exit MSConfig
2. d/l and install an applet called EasyBCD 1.7.2 (or later, Google: EasyBCD) which supports many features of Windows 7.
3. Go into Advanced Options in EasyBCD and select "Limit Widows to '0' CPUs (Leave 0 to reset)". Click "Apply Settings" and exit EasyBCD.

NOTE: This will force the OS to reset the count to default for the amount of Cores you now have. There is possibly a boot setting that can be added that I may not be aware of to do this same function but this little applet works and does the same thing. Don't muck around with any other setting in this utility if you don't know what you are doing it may leave your computer unbootable and a complete reinstall or long repair may need to be performed. Just make sure this one setting is set to "0"

4. Completely shutdown the OS (not reboot or restart or logout). Correctly Shutdown you computer so the it powers down.
5. upon restart into the OS the Task Manager > Performance tab should now show the correct amount of per core graphs if you have the "One Graph per CPU" option selected. Yay your back in business =)

Notes: Some of these discrepancies will appear if your OS is reading the incorrect amount of cores.

1. Device Manager will show the correct amount of Cores for the PC after the new CPU is installed even tho Task Manager still shows the old amount of cores. This is why you need to preform these steps above to fix this disparity and enable the OS to work with the new additional core.
2. CPU-Z (Google: CPUID CPU-Z) will show an incorrect amount of cores until you preform the above steps.
3. SiSoft Sandra (Google: SiSoft Sandra) will show the correct amount of Cores for the PC after the new CPU is installed even tho Task Manager still shows the old amount of cores. This is why you need to preform these steps above to fix this disparity and enable the OS to work with the new additional core.
4. Reinstalling Windows 7 with the "Upgrade" (not Custom Option) will not fix this issue until the above steps are performed. The reinstall should clear the "Number of Processors" setting in MSConfig but it doesn't! Hence the need to run the above steps and avoid a reinstall which takes greatly more time and still does not fix this issue.
5. In a dual boot (XP/Win7) PC, the XP Task Manager will show the correct amount of Cores in Task Manager > Performance tab even tho the same place under Windows 7 will not! Hence the need to perform the above steps.

This is a rare issue, but if you are upgrading CPUs in the future these are a very important steps to enable your Win7 OS to take advantage of this extra core you are buying. Even tho in places like Device Manager it will show the correct amount of cores the MSConfig setting will override the Device Manager only allow you to work with a lessor amount of cores thereby limiting your CPUs true potential preserving your good investment.

Good Luck! I hope someone who encounters this issue finds their way here after a CPU upgrade or they may rip their hair out and I can tell you from experience I was making the Level 3 tech support at Microsoft rip their hair out when I found this issue lol

I was getting an Experience Index value for Processor of 6.3 when this core was disabled and not showing up in Task Manager > Performance tab. Once the above steps were performed my Performance Index jumped to 6.9! My old Dual-Core CPU was an Experience Index of 6.1 to show you the difference a 3rd core can add to your system. In the future, once I start gently Overclocking my new Triple-core processor (once I get a better CPU cooler) It should exceed 7.2-7.4 or greater Experience Index. =)

TCsenter wrote also:

Some recommendations (make sure you are running as Administrator):

• Run MSConfig -> Change to Boot tab -> Advanced Options -> "Number of Processors", make sure there is no check mark.
• Delete processor entries listed in Device Manager, then reboot and allow Windows to redetect/reinstall them.
• In BIOS, check for an option named Max CPU ID Value or CPU ID Max Val and make sure its set to disabled .  This option is only provided for OS prior to Windows 2000.  Save and Exit BIOS.
• Check for a BIOS update for your system or motherboard.
• Confirm the CPU model is supported by the motherboard