How To Evaluate Clock Speed, Cache, and Bus

rocessor speeds are important indicators of speed, but only when compared with CPUs in the same series. Two other specs—Level 2 (L2) cache and front-side bus (FSB)—also play an important role in overall performance. As for clock speed, a 2.66GHz Core 2 Duo E6700 runs faster than a 2.4GHz E6600, for instance. But it's important to note that clock-speed comparisons aren't valid when looking at different architectures. The lower-end 1.86GHz Core 2 Duo E6300 outperforms the older 3.6GHz Pentium D 960, for instance, and the 2.66GHz Core 2 Duo E6700 bests the 3GHz Athlon X2 6000+ in most benchmark tests. A processor's L2 cache memory speeds up operations by making recently accessed data immediately available to the processor. A larger L2 cache serves up a bigger performance boost on Intel processors than on Athlon 64 X2 chips, due to the methods each chip uses to access memory (more on that later). The FSB determines how fast the processor communicates with the memory controller. It's a factor only on Intel processors, which have varying FSB speeds. A faster FSB can speed RAM-intensive operations. Intel's newest chips use a 1,333MHz FSB. The original Core 2 Duo E6000 series chips employ a 1,066MHz bus, while the E4000 series uses an 800MHz bus. On AMD processors, the memory controller is located on the chip, giving the processor faster access to it; the actual memory transfer takes place over the HyperTransport bus link between the processor and the memory, so FSB ratings aren't an issue with Athlon processors. The effect that cache and FSB have on performance depends on the program you're running. A 1.86GHz Core 2 Duo E6320 can best the 2GHz Core 2 Duo E4400 in some tests, due to its larger cache and faster FSB. Realistically, though, in most operations these differences are small.