AMD's Phenom quad-core processor had a rough launch. It was late, had lower clock speeds than expected, and was slower than Intel's quad-core chips. And just as the chips hit the market, an erratum (error) was discovered in the chip that could cause lock-ups in rare multitasking situations, requiring a BIOS patch that slowed down the chip 10 percent or more.
Now AMD is back with its second-generation, errata-free Phenom X4 chips, which can run at their full potential. At the top of the line is the Phenom X4 9850 Black Edition. The Black Edition moniker signifies that the chip has an unlocked multiplier, offering more flexibility for overclocking. At stock speeds, this quad-core chip runs at 2.5GHz, with 2GHz Hypertransport and memory clocks (compared to 1.8GHz for lower-end Phenom X4s). Along with the 9850, AMD has also introduced the $215 2.4GHz Phenom X4 9750 and the $195 2.2GHz Phenom X4 9550.
These 50-series processors aren't radically different from the first-generation Phenom chips. Clock-for-clock, their performance matches the earlier chips they replace, but without the erratum patch slowdown. The Phenom X4 2.5GHz 9850 gets a slight speed boost over the formerly high-end 2.4GHz 9700, and adds the unlocked multiplier.
The Phenom now runs apps up to 25 percent faster than an Athlon X2 at the same clock rate. Speedup is even greater with multicore-aware programs such as video editors and some games. The Phenom X4 is a true quad-core chip, with four independent cores on a single die; AMD also plans a triple-core Phenom X3 series. Unlike the Athlon X2, the memory controller can run at an independent clock rate. Newer Socket AM2+ motherboards let you install fast 1,066MHz memory or overclock your RAM in a Phenom system without changing the CPU's operating speed.
Though AMD has added new SSE4a multimedia instructions, these aren't entirely compatible with the SSE4.1 instructions used on Intel's newer Core 2 processors, so programs will need to add specific support for them. DivX 6.8, for instance, takes advantage of SSE4.1 on the newest Core 2 CPUs, but defaults to the older SSE2 instructions when running on a Phenom.
