AMD Phenom II X4 955 Black Edition CPU

AMD Phenom II X4 955 Black Edition CPU

Manufacturer: AMD
UK Price (as reviewed): £213.79 (inc. VAT)
US Price (as reviewed): $245 (ex. Tax) MSRP

Today AMD launches its fastest CPUs to date: the 955 Black Edition and 945 CPUs, which are built using 45nm Phenom II (K10.5) technology, running at 3.2GHz and 3.0GHz respectively. Unlike the 940 and 920 released in January, these CPUs are AM3 based affording a DDR3 and DDR2 dual memory controller crammed inside.

Despite the fact it takes up more die space and the DDR3 memory controller is somewhat limited to just 1,333MHz with four DIMMs or 1,600MHz with just two, we think AMD is onto a winner because it affords a cheap upgrade for current AM2+ owners, or those who can only afford one of the very cheap 4GB 1,066MHz DDR2 kits out now, as it still offers a clear upgrade path. This is what the 940 lacked, and despite the fact we recommended the CPU at the time, it's partly why we don't recommend it in our monthly buyer's guides.

The 955 is another Black Edition product, meaning that it features an unlocked multiplier, affording much easier overclocking by just cranking it up without taking the more sensitive HyperTransport out of spec. The 945 doesn't follow the same dark trend, but like all 45nm Phenom IIs, the northbridge frequency is free and happy to overclock with extra frequency and voltage, affording directly improved memory performance given the right motherboard.


AMD's three number naming scheme can be deciphered as:

• 900-series - quad-core - 6MB L3 cache
  
• 800-series - quad-core - 4MB L3 cache
  
• 700-series - triple-core - 6MB L3 cache

Although the secondary numbers are somewhat more confusing:

• x55 - 3.2GHz (AM3)
  
• x45 - 3.0GHz (AM3)
  
• x40 - 3.0GHz (AM2+)
  
• x20 - 2.8GHz
  
• x10 - 2.6GHz
  
• x05 - 2.5GHz

Phenom II socket AM3 CPU details

• L1 Cache: 64KB L1 data, 64KB L1 instruction per core, exclusive
  
• L2 cache: 512KB per core, exclusive
  
• L3 cache: 4-6MB accessible by all cores
  
• Hyper Transport and Northbridge Frequency:
  
• 2.0GHz (4.0MT/s) HT 3.0 16-bit bi-directional
  
• 128-bit dual channel or two 64-bit single channels DDR2-1,066MHz or DDR3-1,333MHz (or 1,600MHz OC)
  
• ~758 Million transistors, 258mm² die size
  
• TDP: 125W for both 945 and 955 CPUs

As the transistor count is exactly the same for 45nm AM2+ CPUs as it is for AM3 CPUs, we can only assume the cores are identical but AMD chose to disable DDR3 support in the other products, in addition to a different physical package pin-out to the 938-pin AM3 CPUs. It's rare to progress to a new socket and see a drop in the number of pins, but this is how AMD has made AM2+ CPU not fit in a 938-pin AM3 motherboard socket, but to allow AM3 processors to fit in AM2+ boards.