Question regarding cores

On my small machine (AMD Athlon 64 X2 5000+) in Sensor status window it shows the 2 cpu cores...
On my Main machine (AMD Phenom II X4 955 Black Edition) in Sensor status window it only shows 1 of the 4 cpu cores..

Have I not got something setup right?
That's because your newer machine's CPU (AMD Family 10h-based) features only a single diode for CPU temperature measuring. There might be different tools that display temperatures for each core, but those tools just mirror the same temperature for all cores. So it's physically not possible to get per-core temperature reading on those CPUs.