Question : Why is nmon showing 8 CPU when I have 4 physical CPU and no partitions?

nmon when run on AIX 5.x is showing 8 CPU on a 4 way non partitioned box.  Our 8 way is showing CPU of 16 when viewed with nmon.  Can anyone explain to me why this is?

Answer : Why is nmon showing 8 CPU when I have 4 physical CPU and no partitions?

No it's really due to the SMT feature on the chip.

SMT, or Simultaneous Multi-threading is a hyperthreading design. Somewhat like Intel's Pentium 4 HT. Which also doubles the amount of cpus in Windows. It makes each core capable of running two threads at once.  The OS "sees" the SMT feature as a logical cpu apart from the physical cpu or core if you will.