Opteron's are the workstation/server version of AMD 64bit processor
Athlon 64's are the desktop/home version of AMD 64bit processor
both are 64bit, but opterons support more memory and come dual cpu and quad cpu flavours(actually can be in 8 ways systems)
To be a little bit more precise:
Athlon64 / AthlonFX are CPUs for the desktop market.
Opteron CPUs are for the workstation / server market.
Both types of CPUs have the ability to execute 64bit commands and to handle more memory without any additional logic than any 32bit CPUs before.
In the desktop segment you have to devide Athlon64 and AthlonFX CPUs. The AthlonFX CPUs can handle a so called dual-channel memory configuration which will provide a better overall performance. These are the most expensive and fastest desktop CPUs.
The Athlon64 CPUs are not as expensive but almost as fast as the FX-models. They can be combined with usual boards and memory and perform very well.
Opterons are split up into three families:
1xx, 2xx, 8xx.
1xx (eg. 140, 144, 152) are for single CPU (workstation) systems. They are very (at least 99%) similar to the 940pin AthlonFX-CPUs. An Opteron 1xx that is clocked at the same frequency as the AthlonFX will cost more but won't give you a higher value in your system.
2xx (eg. 240, 246, 252) are for dual CPU systems. These CPUs have one coherent HT-link that is able to connect to another CPU. Opteron 2xx CPUs are more expensive than 1xx CPUs but not faster (per CPU) when clocked at the same frequency. Nevertheless you can use an Opteron 2xx as a single CPU which makes only sense if you have a dual-CPU board and plan to upgrade to a second CPU.
8xx (eg. 842, 844, 850) are for multi-CPU systems with up to 8 CPUs. These CPUs have three coherent HT-links and are the most expensive AMD-CPUs on the market. They are build for multi-CPU (often quad) CPU servers. Nevertheless you should be able to use them in single or dual CPU systems as well but they won't perform better than 1xx or 2xx CPUs.
There are also "HE" and "EE" models of the 8xx Opterons that produce less heat and require less power. These models are compareable to the "Low voltage" CPUs build by Intel.
All Opteron CPUs require ECC REGISTERED memory to operate (which is expensive compared to "usual" PC3200 memory for desktops).
So if you plan to build a "usual" desktop PC you are best of buying a Athlon64. It performs as well as an Opteron but will cost about the half.
AMD64 is the name of the 64bit commands so Opteron CPUs AND Athlon64 CPUs have the AMD64 technology integrated.
I hope this helped.
·CPUs - 2*Opteron 246
·Mainboard - Tyan Thunder K8W S2885ANRF
·RAM - 4*Corsair TwinX1024RE-3200LL (4GB, 8*512MB, DDR400, 2-3-2)
·Graphics - HIS IceQ-II X800Pro
·HDD - Western Digital Raptor WD740GD, 74GB, 10k
·RAID - 3Ware 7850, 64bit PCI, 8chn hardware RAID
·RAID-HDDs - 5*WD800JB
·Optical - 1*SlimSize CD-ROM; 1*NEC7441 DVD-RW
·Sound - Creative SoundBlaster X-Fi Elite Pro