Phenom II - Features

Features

The Phenom II triples the shared L3 cache size from 2MB (in the original Phenom line) to 6MB, leading to benchmark performance gains as high as 30%. In another change from the original Phenom, Cool'n'Quiet applies to the processor as a whole, rather than on a per-core basis. AMD implemented this to address the mishandling of threads by Windows Vista, which can cause single-threaded applications to run on a core that idles at half its clock rate. This feature can be disabled through BIOS options on most motherboards, which allows for customization and overclocking. Due to the nature of this feature, it reduces the effectiveness of overclocking the CPU and RAM, but also decreases power consumption and heat output.

Socket AM2+ versions of the Phenom II (920, 940) lack forward-compatibility with Socket AM3. Socket AM3 versions of the Phenom II are backwards-compatible with Socket AM2+, though this is contingent on motherboard manufacturers supplying BIOS updates. In addition to the Phenom II's pin compatibility, the AM3 memory controller supports both DDR2 and DDR3 memory (up to DDR2-1066 and DDR3-1333), allowing existing AM2+ users to upgrade their CPU without changing the motherboard or memory. However, similar to the way the original Phenom handled DDR2-1066, current Phenom II platforms limit the usage of DDR3-1333 to one DIMM per channel; otherwise, the DIMMs are under clocked to DDR3-1066. AMD claims that this behaviour is due to the BIOS, not the memory controller, and plans to address it with a BIOS update. The dual-spec memory controller also gives motherboard manufacturers and system builders the option of pairing AM3 with DDR2, as compared to competing chips from Intel which require DDR3.

"Thuban" and "Zosma" Phenom II processors support AMD's Turbo Core overclocking performance-boost technology. When not all cores are needed, the processor will automatically overclock up to half of the cores by up to 500 MHz, leaving the other half idle. In turn, when the application demands more than half of the cores, the processor will run on standard clock rate and with all cores enabled.

Some top-level AM3 processors (x945 125W, x955 and x965) require a special power-supply feature, often called "dual power-plane". It's supported by default in all native AM3 mainboards, however not in most AM2+ mainboards, even those advertised as "AM3 optimized" or "AM3 ready". Processor running below its nominal speed (i.e. at 800 MHz), clock and multiplier locked are symptoms of this incompatibility. This is caused by the processor itself: when it detects that the motherboard does not supply dual power planes, the chip locks its multiplier to 4x. This issue is not resolvable via a BIOS update; however, users of AM2 and AM2+ motherboards can still use Phenom II processors excluding the 125 watt variants.

Beginning with the AM3 versions, Phenom II CPUs are based on two dies: the original Deneb die with four cores and the new Thuban die with six. These are divided into five series for marketing. The first two series are flagships based on full dies. The other three series are formed from Deneb dies by die harvesting, that is, chips that were produced with some amount of defects. The affected portions of these chips are disabled and the chips themselves marked as a lower-grade product.

• 1000T series: Flagship X6 series with full complement of cores, L3 cache enabled and Turbo Core.
• 900T series: Based on X6 series but with two cores disabled and Turbo Core.
• 900 series: X4 series with full complement of cores and L3 cache enabled.
• 800 (original) series: These are X4 chips with some amount of defect in the L3 cache; 2 MB is disabled, leaving the chip with 4 MB L3 cache and fully operational cores. Available as model 805, 810, 820 and 830.
• 800 (second) series: These are chips based on the Athlon II Propus quad-core without L3 cache albeit marketed as Phenom II, available as model 840 and 850
• 700 series: These chips have one core disabled, leaving them with three operational cores (marketed as "X3") and a fully operational L3 cache.
• 500 series: These chips have two cores disabled, leaving them with two operational cores (marketed as "X2") and a fully operational L3 cache.

Some versions of the Phenom II X2 and X3, however, have no defects in the silicon but one or two cores "deactivated" to enable AMD to target the lower end of its market. As a result, with the correct motherboard and BIOS it is possible to unlock the deactivated core(s) of the processor. However, success is not guaranteed, because in some cases the core(s) may have been deactivated due to faulty silicon. Hardware enthusiast websites have collected and summarized anecdotal reports that, overall, indicate about a 70% success rate, but these reports likely have self-reporting bias, and more importantly, it is impossible to know whether an unlocked core is truly bug-free.