'Newcastle' is the codename for older 130nm SOI parts (revision CG), whereas 'Venice' is the codename for the newer 90nm SOI parts (revision E3).
Due to its smaller 90nm SOI manufacturing process, Venice parts have a slightly lower core-Voltage (Vcore) and will consequently consume slightly less power on average (e.g. 67W max. TDP for a 3500+ model vs. 89W max. TDP for the same model with the older 130nm SOI 'Newcastle'-core).
Furthermore, being a newer revision, a 'Venice' part has a slightly improved memory-controller (better compatibility when running more than two DIMMs at DDR400) as well as SSE3-support.
You can determine whether an Athlon 64 processor uses a 'Newcastle' or 'Venice'-core by looking at its OPN (Ordering Part Number):
A Newcastle-part's OPN will end in '...AW' whereas a Venice-part's OPN will end in '...BP'.
Example (Athlon 64 3500+):
'ADA3500DEP4AW' - Newcastle, 130nm SOI, rev. CG
'ADA3500DAA4BP' - Venice, 90nm SOI, rev. E3
For retail/boxed parts, the OPN would be as follows:
'ADA3500BOX' - Newcastle, 130nm SOI, rev. CG
'ADA3500BPBOX' - Venice, 90nm SOI, rev. E3
Note: The OPNs mentioned above apply to 939-pin parts.
There are also 754-pin Newcastle (but no Venice) parts, but I wouldn't recommend buying into the older 754-pin platform (for upgradeability reasons) unless you're on a really tight budget and don't plan to upgrade for awhile.
The opinions expressed above do not represent those of Advanced Micro Devices or any of their affiliates.
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