Why /proc/cpuinfo output does not show correct available number of cpu cores in RHEL5?

Issue

• /proc/cpuinfo not showing number of cores.
• vm is hosted on vmware ESXi.

# cat /proc/cpuinfo
processor       : 0
vendor_id       : GenuineIntel
cpu family      : 6
model           : 15
model name      : Intel(R) Xeon(R) CPU           X5667  @ 3.07GHz
stepping        : 1
cpu MHz         : 3059.000
cache size      : 12288 KB
fpu             : yes
fpu_exception   : yes
cpuid level     : 11
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov         pat pse36 clflush dts acpi mmx fxsr sse sse2 ss syscall nx lm constant_tsc ida n        onstop_tsc arat pni ssse3 cx16 lahf_lm
bogomips        : 6118.00
clflush size    : 64
cache_alignment : 64
address sizes   : 40 bits physical, 48 bits virtual
power management: [8]