Corollary: Are all memory chips therefore dual channel compatible?
Dual channel is always a motherboard feature, there is no
difference in the memory (chips, PCB, or timings for dual
channel). Many times manufacturers (or resellers) will
simply market it as such "dual channel" memory.
Another question: How can one tell whether RAM is being accessed at a dual
channel speed?
Your BIOS may list it in the information screen when it
POSTs. Some utilities might tell you, though I don't know
which ones- you could Google for some.
Also benchmarks should reveal it, bench the memory with a
single module and compare to having two modules installed.
If two modules are faster that is evidence of dual channel
mode, as ANY properly working bios should at very most, have
same memory parameters with more memory modules installed
but often slower as a result (unless you were manually
changing the memory related settings). Thus, two memory
modules not in dual channel mode would not be faster than
either of the modules alone, presuming that you at least
have enough memory that the system isn't using the pagefile
for virtual memory during the testing.