I have a strange situation. I have two computers with identical hardware, both Core i5, exactly the same model. The only difference is the OS, one has 12.04 32-bit and the other one has 12.04 64-bit.

The problem is that hyperthreading is only enabled on the 32-bit OS and not on the 64-bit OS. Can you tell me why, and how I can enable it?

I looked in the BIOS and both have exactly the same settings, both hyperthreading enabled in BIOS but not in the OS.

2 logical processors:

 Architecture:          x86_64  

CPU op-mode(s):        32-bit, 64-bit  

Byte Order:            Little Endian  

CPU(s):                2  

On-line CPU(s) list:   0,1  

Thread(s) per core:    1  

Core(s) per socket:    2  

Socket(s):             1  

NUMA node(s):          1  

Vendor ID:             GenuineIntel  

CPU family:            6  

Model:                 42  

Stepping:              7  

CPU MHz:               2294.665  

BogoMIPS:              4589.73  

Virtualization:        VT-x  

L1d cache:             32K   

L1i cache:             32K  

L2 cache:              256K  

L3 cache:              3072K  

NUMA node0 CPU(s):     0,1 

4 logical processors:

Architecture:          i686  

CPU op-mode(s):        32-bit, 64-bit  

Byte Order:            Little Endian  

CPU(s):                4  

On-line CPU(s) list:   0-3  

Thread(s) per core:    2  

Core(s) per socket:    2  

Socket(s):             1  

Vendor ID:             GenuineIntel  

CPU family:            6  

Model:                 42  

Stepping:              7  

CPU MHz:               800.000  

BogoMIPS:              4589.36  

Virtualization:        VT-x  

L1d cache:             32K  

L1i cache:             32K  

L2 cache:              256K  

L3 cache:              3072K