AMD’s Sempron processor can be found in two different socket types: 462 and 754 (these numbers refer to the kind of motherboard necessary to install the processor). Socket 462 is the same socket type used by Athlon XP and Duron processors, while socket 754 is the same used by Athlon 64 processors (there are Athlon 64 models that use a different kind of socket, called 939).
Thus, Sempron processors based on the socket 754 pinout use the same motherboard originally designed for Athlon 64 CPUs. Actually, these processors are in fact Athlon 64 CPUs with less L2 memory cache and with the 64-bit instruction set disabled.
However, since last June AMD decided to activate the 64-bit extensions on socket 754 Sempron processors. Because of that there are Sempron processors on the market that have these instructions and processors that don’t have them. How can we detect if a Sempron CPU has the 64-bit instruction set?
There are two ways. The first one is looking on the processor metallic plate to see what is written on it. If the two letters of the first line are “BX” it means that this model has the 64-bit instruction set. For example, “SDA3100AIP3AX” indicates a Sempron 3100+ without the 64-bit instruction set, while “SDA3100AIO3BX” indicates a Sempron 3100+ with the 64-bit instruction set.
The second way of detecting if a socket 754 Sempron CPU has the 64-bit extensions is running a program like CPU-Z (http://www.cpuid.com/cpuz.php). If it is listed “x86-64” under “Instructions” it means that the CPU has 64-bit instructions.