Oracle documentation states the default value of CPU_COUNT is 0 / zero.
But if you do not set this parameter – and allow it to default – or purposely set it to 0 / zero – and then show the parameter – and you won’t ever see 0 / zero – you’ll see the #CPU*#SMT (in my example below #CPU=24 and #SMT=2
alter system set cpu_count=0 scope=both;
show parameter cpu_count
So much for the Oracle documentation…
By the way, on Intel’s platform SMT is also referred to as Hyper-Threading and is always 2 – if it is turned on (normally done in the Intel BIOS). Other hardware vendors have differing SMT values and in some cases allow you to modify this number on the fly (see 870 IBM Frames where SMT can be set as high as 8).