What’s new with the Athlon 64 and Athlon FX.

Apart from 64-bit instructions the Athlon 64 and Athlon FX feature a number of significant enhancements over the now four year old Athlon (K7) architecture. These enhancements include:

• Integrated Memory controller – Dual channel ECC registered DDR 400 for Athlon FX or Single Channel DDR 400 for Athlon 64
• SSE 2 instruction set support
• 600/800 MHz DDR HyperTransport link to AGP tunnel and SouthBridge controller
• 12 stage integer pipeline (Athlon featured 10 stages)
• 17 stage Floating Point pipeline (Athlon featured 15 stages)
• 128-bit memory access to two DIMM modules
• Deeper Integer buffers, increased from 3x6 to 3x8
• Level 1 cache Translation Lookaside Buffer (TLB) increased to 40 entries
• Level 2 cache TLB increased from 256 entries to 512
• Enhanced branch prediction

Essentially the Athlon 64 and Athlon FX build upon the proven design principles which were present in the Athlon (and can trace their ancestry back to the K5), with AMD choosing to evolve it’s existing chip as opposed to starting with a more radical design such as the route followed by Intel when it moved from the P6 core to the Pentium 4. As a result many of the core design features present in the Athlon have found their way into the Athlon 64/FX, with some of the more significant being:

Interestingly AMD have opted not to equip the Athlon 64/FX with two of the more notable features present in the Pentium 4. The first of these being the trace cache design which replaced the traditional Level 1 cache SRAM with smaller 8-byte amounts placed along the various pipelines. AMD have opted to stay with the more traditional 128 KB Level 1 cache which is divided into 64 KB Instruction and 64 KB Data cache.

As the pipelines of the Athlon FX and 64 have increased so has the need to improve the Branch prediction unit on the K8 core. This has been enhanced along with additions to the Translation Lookaside Buffers.

The other significant feature present on the Pentium 4 which is not available on the Athlon 64/FX is HyperThreading support. At present the Athlon 64/FX designs will be firmly single-threaded.

Common features of the Athlon FX and Athlon 64 include:

• 128 KB Level 1 cache (unchanged from Athlon XP)
• 1 MB Level 2 exclusive cache (doubled from Athlon XP “Barton”)
• 0.13 micron “Silicon On Insulator fabrication
• 105 million plus transistors (the effect of the increased L2 cache)
• 1.5v core voltage

Interestingly AMD are entering the 64-bit CPU market with two separate chip designs. These being the Athlon FX and the Athlon 64.

x86-64.

Athlon FX/64 - Performance.