I recently purchased an AMD Phenom II X4 955. After installing it and checking AMD Overdrive, I noticed that only CPU 0, CPU 1, CPU2 are recognized. I downloaded CPU-Z , ran it, and it also showed only 3 cores. However, through Device Manager, it shows 4 cores are being recognized. And BIOS shows 4 cores.
I am not entirely sure which one to rely on given that they all show different results.

I have tried unlocking the 4th core but I get the same results.
Here are my specs:
motherboard: GIGABYTE GA-790XT-USB3 (BIOS updated)
OS: Windows 7 Ultimate 32-bit

Thanks alot.

Is this a all new build or just upgrading?

If upgrading what cpu did you have before?

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PII 1100T (Extinct)
Asus M4A78T-E (should be Extinct)
4Gb of Corsair XMS3 1600Mhz DDR3 (Going strong)
2x1GB 5850's (On their last lags)
Corsair HX850W (Awsome)
NZXT Phantom case (too ***** big)

I have similar kind of problem like yours. I have AMD Phenom II X2 555 3.2GHz. When I unlocked, it show Phenom II x4 but only shows 1 core in CPU-Z. In Device Manager shows 4 cores. HELP!

Go into device manager and verify if you've got drivers attached to the processor. If you do, remove those drivers and reboot the system.

sswilson, already tried uninstall and reboot, still same.... also reset the bios but fail.

There's a process to get windows to have a second look at how many cores there are (google), but if it were me I'd just do a fresh install.

I had this problem too on a Gigabyte 890 GX mobo. I'd been troubleshooting and turned on "Bootlogging". I spec'd "2 cores" and "maxmem". This was fine. However, it added to the boot.ini file /.../bootlog /maxmem=2048 /numproc=2

When I decided to try running 4 cores again, it kept seeing /numproc=2 and even though bios had all the settings OK, as soon as windows started - poof! two cores lost.

So I changed the boot.ini file back - removed bootlogging, BUT left /numproc=4 and presto - 4 cores are running again!!! [Phenom II BE550]

I think a lot of people are having this problem if still running XP. Cheers

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Maxing Clocks Is Sweeter Than Sex!!!

You can make these changes in msconfig.exe>Boot tab>Advanced radial.

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The opinions expressed above do not represent those of Advanced Micro Devices or any of their affiliates.

Quite right - I gues there are several ways. But it had me foxed and went looking for answers. I saw many posts of folk spending on mobo to get the unlock feature, and wringing hands because they had 4 cores and lost two in short order.

Some of the advice given was complete reinstal and other draconian stuff - and I was going to restore to a previous wim image too - then discovered it by accident.

It looked pretty hopeless and very disappointing - some sad folk thingking core unlock was all hype. One post claimed AMD were sending secret code to "micro-update" and get back at the mobo makers for spoiling their $$.

Like a lot of wiered stuff - turns out to be a simple but frustrating fish hook. And there might be many more like it lurking about!! Cheers.

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Maxing Clocks Is Sweeter Than Sex!!!