Why Red Hat Enterprise Linux 4 system detects only one CPU on multi-core server ?

Issue

• Physical server have 2 Dual-Core Intel Xeon, 3000 MHz processor and running with RHEL-4.9 (2.6.9-103.EL).
• While checking the /proc/cpuinfo file for cpu details, it is showing CPU details of only one CPU core.

# cat /etc/redhat-release
Red Hat Enterprise Linux AS release 4 (Nahant Update 9)

# cat /proc/cpuinfo
processor       : 0
vendor_id       : GenuineIntel
cpu family      : 6
model           : 15
model name      : Intel(R) Xeon(R) CPU            5160  @ 3.00GHz
stepping        : 11
cpu MHz         : 3000.115
cache size      : 4096 KB
fpu             : yes
fpu_exception   : yes
cpuid level     : 10
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 ht tm syscall lm pni monitor ds_cpl est tm2 cx16 xtpr lahf_lm
bogomips        : 6030.28
clflush size    : 64
cache_alignment : 64
address sizes   : 38 bits physical, 48 bits virtual
power management: