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I am a little bit surprised with the following information that I get with dmidecode:

srs@ubuntu:~$ sudo dmidecode -t processor
# dmidecode 2.9
SMBIOS 2.6 present.

Handle 0x0004, DMI type 4, 42 bytes
Processor Information
    Socket Designation: LGA1155
    Type: Central Processor
    Family: <OUT OF SPEC>
    Manufacturer: Intel            
    ID: A7 06 02 00 FF FB EB BF
    Version: Intel(R) Core(TM) i5-2500K CPU @ 3.30GHz       
    Voltage: 1.0 V
    External Clock: 100 MHz
    Max Speed: 3800 MHz
    Current Speed: 3300 MHz
    Status: Populated, Enabled
    Upgrade: Other
    L1 Cache Handle: 0x0005
    L2 Cache Handle: 0x0006
    L3 Cache Handle: 0x0007
    Serial Number: To Be Filled By O.E.M.
    Asset Tag: To Be Filled By O.E.M.
    Part Number: To Be Filled By O.E.M.
    Core Count: 4
    Core Enabled: 1
    Characteristics:
        64-bit capable

However from gnome-system-monitor I can see 4 CPU working at the same time.

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Probably a power saving feature of the CPU, you don't need them to be active all the time, only when they're needed. –  Uri Herrera Aug 29 '12 at 8:18
    
@Uri Herrera. I think I am probably misunderstanding the difference between processor and core. I m supposed to have 4 processors inside an Intel i5 2500k, perhaps each of these processors have got 4 cores, I don't know. –  Salvador Aug 29 '12 at 8:34
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2 Answers

up vote 2 down vote accepted

Section 7.5.7 of the SMBIOS specification (http://dmtf.org/sites/default/files/standards/documents/DSP0134_2.7.1.pdf) states:

"Core Enabled is the number of cores that are enabled by the BIOS and available for Operating System use. For example, if the BIOS detects a dual-core processor, it would report a value of 2 if it leaves both cores enabled, and it would report a value of 1 if it disables multi-core support."

If you are seeing 4 CPUs online then I personally suspect that this maybe just a goof-up in the SMBIOS table.

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This information about SMBIOS is very useful for me to notice that there a few things that do not properly work at my MotherBoard. Now I am going to update its BIOS, before I ask anything else. Thanks. –  Salvador Aug 29 '12 at 11:49
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1.- According to http://software.intel.com/en-us/articles/intel-hyper-threading-technology-your-questions-answered/ How can I tell if my system is using Hyper-Threading Technology? it seems that the Intel® Hyper-Threading Technology in fact duplicates the available CPUs

2.- The lshw command only says that there are 4 physical id, physical id: 4

3.- /pro/cpuinfo

srs@ubuntu:~$  cat /proc/cpuinfo | grep -e processor -e "model name" -e "cache size" -e "physical id" -e "siblings" -e "core id" -e "cpu cores"
processor   : 0
model name  : Intel(R) Core(TM) i5-2500K CPU @ 3.30GHz
cache size  : 6144 KB
physical id : 0
siblings    : 4
core id     : 0
cpu cores   : 4
processor   : 1
model name  : Intel(R) Core(TM) i5-2500K CPU @ 3.30GHz
cache size  : 6144 KB
physical id : 0
siblings    : 4
core id     : 1
cpu cores   : 4
processor   : 2
model name  : Intel(R) Core(TM) i5-2500K CPU @ 3.30GHz
cache size  : 6144 KB
physical id : 0
siblings    : 4
core id     : 2
cpu cores   : 4
processor   : 3
model name  : Intel(R) Core(TM) i5-2500K CPU @ 3.30GHz
cache size  : 6144 KB
physical id : 0
siblings    : 4
core id     : 3
cpu cores   : 4

4.- Understanding Linux /proc/cpuinfo: Single socket Quad Core (Example 3):

Notice how each processor has its own core id. The number of siblings matches the number of cores so there are no Hyperthreading siblings. Also notice the huge l2 cache - 6 MB. That makes sense though, when considering 4 cores share that l2 cache.


In consequence, maybe dmidecode is trying to tell the number of hardware threads per core. As far as my processor does not support Hyper-Threading Technology, it has got only one hardware thread per core.

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