Core Duo, and Core 2 Duo are processor families from Intel. They're the successor to the Pentium and Celeron families. Dual core simply means there's 2 processor cores on one processor package. It's effectively the same as running two physically separate CPU packages with a traditional one core. Core 2 Duo is dual core, but so are most, if not all Pentium D processor, various Xeon (Intel's server-oriented CPU's), AMD's Athlon64 X2 series, as well as their server chip, Opteron.