For Socket F and Socket AM2 Opterons, each chip has a four-digit model number, in the form Opteron XZYY. For all Opterons, the first digit (the X) specifies the number of CPUs on the target machine:
1 - Designed for uniprocessor systems
2 - Designed for dual-processor systems
8 - Designed for systems with 4 or 8 processors
For Socket F and Socket AM2 Opterons, the second digit (the Z) represents the processor generation. Presently, only 2 (dual-core), DDR2, 3 (quad-core) and 4 (six-core) are used.
For all Opterons, the last two digits in the model number (the YY) indicate the clock frequency of a CPU, a higher number indicating a higher clock frequency. This speed indication is comparable to processors of the same generation if they have the same amount of cores, single-cores and dual-cores have different indications despite sometimes having the same clock frequency.
The suffix HE or EE indicates a high-efficiency/energy-efficiency model having a lower TDP than a standard Opteron. The suffix SE indicates a top-of-the-line model having a higher TDP than a standard Opteron.
Source[ Wikipedia ]