Dual Core vs. Dual CPU

[Urs Thuermann <urs@xxxxxxxxxxxxxxxxx>]

I'd like to know what is the difference between a system with a dual
core CPU compared to two (single core) CPUs.  I know dual core means
two CPUs on one chip, but is it really two complete CPUs or do they
share some component which is used by both CPU cores?

For example HT duplicates only those parts of CPU which hold the state
of the program in execution (i.e. program counter, registers, etc.)
but they share the execution logic which often leads to performance
loss. 

Is there some performance difference between dual core and two real
CPUs, too?  I assume the dual cores on one chip must share the bus
interface, but since in a multi CPU system only one CPU can access the
bus at a time, I think this doesn't make a performance difference,
right?

Can anybody give some clarifiactions on these issue?

urs
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