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AMD Phenom X4 B3 Stepping Analysed

By: Cameron Johnson | AMD CPUs in CPUs, Chipsets & SoCs | Posted: Apr 8, 2008 4:00 am

Phenom Enters the Ring



Phenom is the first K10 processor to make it out of the AMD production line. Phenom is the replacement for the aging Athlon 64 series of CPU. Phenom is a direct drop in replacement for motherboards designed to take 65nm series Athlon 64 Processors on the AM2 socket, Yes, that's right, if you have a board that supports a 65nm Athlon 64 you can drop this baby straight in.



While being compatible with socket AM2, there are a few things you will need to be aware of. First off is the Split Power Plane system which will not work under AM2 based boards, only AM2+ boards support this. That means that you will not be able to run DDR2-1066MHz memory certified for the Phenom unless you actually overclock the FSB to increase memory speeds. The dividers that handle this will not be available on AM2 boards. Next is the HT3.0; running the Phenom on an AM2 board defaults the interconnect speeds back to HT 2.0 specs, resulting in a lower overall bandwidth between the CPU and external Northbridge. Also, you will not be able to run the advanced power management of the HT3.0 bus, resulting in higher power consumption.



AMD has gone to a lot of trouble to make sure that if you simply want to upgrade the CPU first rather than go for a full system upgrade, Phenom will slot in. But to get all of the extra benefits including control of individual core speeds and split plane voltage for higher speed DDR2 memory, you're going to need a HT3.0 based board using the AM2+ socket.



Moving on, we opened up CPU-Z to get a bit more information on the Phenom 9850 we were sent. The Phenom X4 is based on the Agena core with a 65nm die production. The Phenoms with a xx50 number will be based on the B3 revision that has the TLB fix incorporated, allowing the use of the L3 cache.



AMD has also finally done away with the older memory dividers that has plagued them with inconsistent speeds. In the past, Athlon 64 X2's and the like have used a memory clock ratio that is divided by the CPU ratio. That is, if the CPU ratio is 7x, the memory clock is divided by 7 to get the bus speed. This has led to clock inconsistencies where some CPUs could not run true DDR2-800MHz speeds. Thanks to a constant rate Northbridge clock that is independent of the CPU, the memory ratio can now be set by a ratio divider.



It certainly wouldn't be a review if we didn't try to overclock the CPU. We used our water cooling rig in order to remove as much heat as possible from the system to try and get as high a clock speed as possible. Thanks to the 9850's Black Edition state, its CPU clock ratios are completely open to manipulation. We didn't go up on the FSB as we didn't want to have this as a cause of any instability issues, so we limited it to ratio adjustments. Our final result was 2.7GHz stable using 1.336v on the CPU. We did get 2.8GHz to load windows, but as soon as we started to even think about running any benchmarks the system would instantly crash. It looks like the current 65nm range hits a wall at 2.7GHz or there abouts. With further cooling it might be possible to get higher, such as the use of LN2 or vapour phase change.



AMD has also upped the stakes by aiming Phenom at overclockers and performance users. AMD Overdrive is a Windows based overclocking utility that when combined with an AMD Phenom X4 or X3 processor allows you to be able to control the FSB, CPU multiplier, memory multipliers, voltages and various other features.


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