Phenom C2 and C3 CPUs are designed for use in desktop processors.
In CPU design, "stepping" refers to incremental changes made to a CPU's architecture to improve performance or make minor tweaks. The Phenom II line of processors made by AMD comes in both C2 and C3 designs, the latter identifiable by an "M" at the end of the model number. C3 designs are more power-efficient and substantially better for computer "overclockers" who push their CPUs to the absolute limit.
History
The C2 line of Phenom processors was introduced in early 2009 with the first of the Phenom II series of CPUs. These were intended to succeed the first Phenoms, launched the previous year. The C3 revision, which introduced generally incremental changes to the basic Phenom design, first appeared in late 2009 and by 2010 had become the standard physical design for Phenom CPUs; 6- and 4-core Phenom II processors on the E0 stepping, which follows the C3 design, launched in late 2010.
Chip Design
In most respects, the C3 and C2 line of processors are identical. The C3 revision introduced minor changes, most concerning power management and efficiency. For example, the C1E "Enhanced Halt State" is included in C3 chips, which allows them to throttle their speed back when the CPU is not being heavily utilized. Overall, C3 chips are designed to use less power, which also helps them to generate less heat. For power users needing to get the most out of their computers, the C3 revision also allows all 4 memory slots to be filled with high-speed memory without any problems.
Speeds
In terms of maximum clock speed, the C2 and C3 lines of Phenom processors are relatively similar. Indeed, AMD offered a number of CPUs, like the X4 965 and X4 955, in both C2 and C3 variants. Later high-speed Phenoms, however, such as the 3.6 GHz 975 and 3.7 GHz 980, were only available in C3 form. In real-world usage, the aggressive CPU throttling offered by the energy-efficient C3 stepping means that reported CPU speed may fluctuate drastically as the computer slows itself down to help save power.
Overclocking
The C3 design, which helps the CPU run cooler and with less power, also helps in "overclocking"---a practice in which computer enthusiasts tune the processor to run faster than it was originally designed, at the expense of drawing more power and creating more heat. C3 processors overclock better than C2 processors of otherwise-identical specifications. With a minor increase in power consumption, for example, a C3 965 processor, traditionally clocked at 3.4 GHz, can be pushed to over a 4 GHz without a loss of stability.
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