Can I use Opteron to configure a desktop PC?
Why Athlon 64 FX is more expensive than just Athlon 64 ?
In short, it's better.
According to AMD fans, it's simply the best CPU you can get for your PC. It was made for cinematic purposes - great for games, graphics, photo/video editing.
On PCWorld, the fastest PCs are always running the FX but they get lower ratings due to the higher price.
PCWorld Top 15 Desktops
I've heard of small businesses doing this. The FX or basic AMD64 should have more than enough speed for tough computing tasks. If you want 64-bit technology, go with one of those.
Athlon 64, Athlon FX, Sempron, Opteron
The FX is sold unlocked for overclocking and also plugs into socket 940 which uses the faster HyperTransport bus. The Athlon 64 plugs into the old and slower socket 754, unless they are the newer more-expensive ones which use the new HyperTransport-enabled socket 939 (which also has the added speed advantage of not requiring registered memory). Also, some of the Athlon 64 models only have 512K of L2 cache.
If you want Athlon 64 speed, but don't need the 64-bit feature, you can choose the higher-end Semprons which are basically Athlon 64s with their 64-bit instruction sets disabled (look for the ones that say, "FSB: Integrated into Chip" -- the other ones are just relabeled Athlon FXs).
Also worth mentioning is that the Opteron 1xx series is a cheaper (because it comes locked) alternative to the socket 940 Athlon FX.
without 64-bit Windows, does it mean Athlon 64 is underutilized?
That seems to be a tautology. The answer is, "Yes. If you are not using the 64-bit extensions to the instruction set, then you are not using the 64-bit extensions to the instruction set. Generally, it might be said that if you are not using something then you are not using that thing."
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