AMD's Athlon 64 FX-51

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The Athlon 64 FX-51 Processor
AMD Drops the Hammer, On Your Desktop!

By, Marco Chiappetta
And Dave Altavilla
September 23, 2003


It has been about two years, since AMD first divulged information about their "K8" architecture, also known as the "Hammer", at the Microprocessor Forum in 2001.  At the time, AMD was having much success with their "K7" line of processors.  Enthusiasts and industry analyst were eager to see just what AMD could do with their next generation processor architecture.  AMD was no longer following in Intel's footsteps.  They were introducing new technology in an effort to become an industry leader and innovator, rather than just a "me too" player.  AMD's break-away technology initiative resulted in the Athlon, which as you probably know, was AMD's most successful line of microprocessors to date.  In the early days of the Athlon, who would have thought AMD could make such a significant dent in Intel's market share?  Home and Enterprise level consumers rejoiced.  Finally, there was real competition for Intel's Pentium.  This rivalry could only result in better technology, at faster design cycles, with lower prices.  The future was bright for Personal and Enterprise computing and it's still getting brighter, here in late 2003.

The "K8" architecture, which has evolved into the Opteron and now the Athlon 64 line of CPUs, is a significantly more radical departure from traditional x86 architectures.  Opterons, Athlon 64s and Athlon 64 FXs would be AMD's first microprocessors built using .13 micron SOI (Silicon-on-Insulator) technology, which ideally would allow for higher clock speeds with lower thermal characteristics.  AMD also planned on pulling the memory controller out of the Northbridge block and incorporating it into the processors die, to reduce latency, which in turn would increase performance even further.  Of course, then AMD decided to execute the boldest move the industry has seen to date, in x86 computing.  As the Athlon 64's branding suggests, AMD's new Athlon would be designed from the ground up as a native 64-bit machine with the capability to also run in 32-bit mode.  Around the time AMD introduced the Opteron, Intel since scoffed at the idea, stating that 64-bit computing will not be required for at least a year down the roadmap.  However, AMD decided to make 64-bit computing a reality, today for the Desktop PC, with the introduction of the Athlon 64 and Athlon 64 FX-51. 

A host of other enhancements were implemented as well, culminating in the product we'll be looking at today, AMD's new flagship desktop CPU, the Athlon 64 FX-51.  The Athlon 64 FX-51 is a 2.2GHz processor, targeted squarely at gamers and enthusiasts, who need the absolute fastest machine available, at almost any cost.  The mainstream Athlon 64 3200+ also debuts today at 2.0GHz, with a price tag that will put it within reach of a much larger audience.


Features & Specifications of the AMD Athlon 64 FX and Athlon 64
Source: AMD

When utilizing the AMD64 Instruction Set Architecture, 64-bit mode is designed to offer:

  • Support for 64-bit operating systems to provide full, transparent, and simultaneous 32-bit and 64-bit platform application multitasking.
  • A physical address space that can support systems with up to one terabyte of installed RAM, shattering the 4 gigabyte RAM barrier present on all current x86 implementations.
  • Sixteen 64-bit general-purpose integer registers that quadruple the general purpose register space available to applications and device drivers.
  • Sixteen 128-bit XMM registers for enhanced multimedia performance to double the register space of any current SSE/SSE2 implementation.

Integrated DDR memory controller:

  • Allows for a reduction in memory latency, thereby increasing overall system performance.

An advanced HyperTransport link:

  • This feature dramatically improves the I/O bandwidth, enabling much faster access to peripherals such as hard drives, USB 2.0, and Gigabit Ethernet cards.
  • HyperTransport technology enables higher performance due to a reduced I/O interface throttle.

Large level one (L1) and level 2 (L2) on-die cache:

  • With 128 Kbytes of L1 cache and 1 Mbyte of L2 cache, the AMD Athlon 64 processor is able to excel at performing matrix calculations on arrays.
  • Programs that use intensive large matrix calculations will benefit from fitting the entire matrix in the L2 cache.

64-bit processing:

  • A 64-bit address and data set enables the processor to process in the terabyte space.
  • Many applications improve performance due to the removal of the 32-bit limitations.
Processor core clock-for-clock improvements:
  • Including larger TLB (Translation Look-Aside Buffers) with reduced latencies and improved branch prediction through four times the number of bimodal counters in the global history counter, as compared to seventh-generation processors.
  • These features drive improvements to the IPC, by delivering a more efficient pipeline for CPU-intensive applications.
  • CPU-intensive games benefit from these core improvements.
  • Introduction of the SSE2 instruction set, which along with support of 3DNow! Professional, (SSE and 3DNow! Enhanced) completes support for all industry standards.
  • 32-bit instruction set extensions.

Fab location: AMD's Fab 30 wafer fabrication facility in Dresden, Germany

Process Technology: 0.13 micron SOI (silicon-on-insulator) technology

Die Size: 193mm2

Transistor count: Approximately 105.9 million

Nominal Voltage: 1.50v




Today, AMD is taking the wraps of two new desktop processors, the flagship Athlon 64 FX-51 and their new performance / mainstream CPU, the Athlon 64 3200+.  The FX-51 debuts at 2.2GHz, while the Athlon 64 3200+ arrives clocked at 2GHz.  The differences don't stop there, however.  As the chart above indicates, the Athlon 64 FX-51 uses a 940-pin package, similar to AMD's Opteron, while the Athlon 64 3200+ uses a 754-pin package.  The Athlon 64 FX-51 also has a memory controller that is twice as "wide" as the 3200+; 128-bits vs. 64-bits respectively.  The Athlon 64 FX-51 also requires registered memory to function, whereas the Athlon 64 3200+ can use standard unbuffered DDR memory.  Registered memory uses an additional "buffer" that isolates memory chip load from the memory controller, which allows for the use of more DIMMS.  ECC memory has extra bits of storage that help in the identification and repairing of errors, hence "ECC" - Error Checking and Correction.  Please don't confuse registered memory with ECC though.  ECC and registered memory types are totally different animals.  It's possible to buy memory that is registered, but not ECC, or vice versa.  Something the chart does not show is the packaging material used for each CPU.  In its current form, the FX-51 is housed is ceramic packaging material, ala the Thunderbird.  The Athlon 64 3200+ is using organic packaging like the current generation of Athlon XPs.  These processors do share many features and enhancements, which is why you're here reading about their release today...


AMD64 - 64-bit Processing: The Athlon 64s, like the Opteron, have the ability to run 64-bit operating systems though the use of a new set of extensions to the x86 ISA (Instruction Set Architecture).  With the 64-bit Itanium, Intel introduced the IA-64 ISA, which has its advantages, but one major caveat with introducing a new ISA and microprocessors that use the new instructions set, is that they are not natively compatible with x86 code.  AMD took a much different approach to 64-bit computing.  They simply extended the x86 ISA to support 64-bit memory addressability. This makes the Athlon 64 natively compatible with current x86 code, while giving it support for 64-bit applications going forward.  Due to the fact that the Athlon 64 can run two different types of code, x86 and AMD64, the CPU operates in two different modes dubbed "legacy mode" and "long mode".  In legacy mode, the Athlon 64 natively runs all 16-bit or 32-bit x86 applications.  In long mode, which requires a 64-bit AMD64 compliant operating system, the Athlon 64 will enjoy all of the benefits of 64-bit computing.  Long mode also has a compatibility sub-mode that allows the running of 32-bit applications with a 64-bit operating system.  The Athlon 64's ability to run all these different types of code make it a very versatile processor.

Integrated DDR Memory Controller: One of the Athlon 64's major new features performance enhancing features is its integrated memory controller.  With most current processors, the Northbridge houses the memory controller, which communicates with the CPU via the Front Side Bus (FSB).  With the Athlon 64, the memory controller is now on the processor's die, which means memory traffic no longer has to travel out of the CPU to chipset and back.  Being that the memory controller is now integrated into the CPU, it will run at the same speed as the host processor.  This type of configuration drastically reduces latency, which should yield significant performance gains.  One negative to having the memory controller integrated into the processor's die is that to support emerging memory technologies, like DDR2 for example, the controller has to be redesigned and the processor needs to be replaced.

An Advanced HyperTransport Link:
AMD has also replaced aging chip-to-chip interconnects with their HyperTransport technology. Today's fastest desktop processors interface with the motherboard's chipset, and subsequently the memory and AGP bus, etc, through the FSB at 200MHz (400MHz effective with the Athlon XP - 800MHz effective with the Pentium 4).  The Athlon 64s, however, are equipped with a HyperTransport link that operates at up to 800MHz DDR (1600MHz effective).  When operating at top-speed, a single HyperTransport link offers a maximum of 6.4GB/s of bandwidth.

Large L1 & L2 On-Die Cache:
In February of this year, AMD released Athlon XPs based on the "Barton" core, with double the amount of on-die L2 cache as the older "Thoroughbred" core.  The Bartons have 512KB of full-speed L2 cache versus the Thoroughbred's 256K.  The Athlon 64s take things a step further with a full 1MB (1024KB) of on-die L2 cache.  This added cache should provide a boost in performance, especially in applications where large amounts of data are being sent to the processor and main system memory. With twice the L2 cache of the Barton based Athlon XPs, the new Athlon 64 core can run a larger chunk of code out of its on-chip cache resources, versus having to fetch it from system memory.  A side effect of having this much L2 cache is that the Athlon 64 now has a die size of 193mm2, almost twice the size of the Athlon XP.  With a die this large, the Athlon 64 is going to be expensive to produce.  AMD claims that when they move to 90nm (.09-micron) manufacturing process next year, the corresponding die shrink will bring the die size on a comparable chip down to a much more palatable 120mm2.

Larger TLBs, Better Branch Predicition, More Counters:
The Pentium 4 has taken a lot of flak because its deep 20-stage pipeline was less efficient than the Athlon XP's 10-stage pipeline.  The deep pipeline is part of what allowed the Pentium 4 to reach such high clock speeds, but it Is also why an Athlon, clocked at a much lower clock speed than a P4, can perform at similar levels.  Clock-for-clock, that Athlon XP can handle more instructions.  With the Athlon 64, AMD has deepened the processor's pipeline to 12-stages, which you'd think would lower the core's IPC (Instructions Per Clock).  However, thanks to some core architectural improvements, it hasn't.  The Athlon 64 has larger Translation Look-Aside Buffers (TLB), with improved latency and improved branch prediction.  The Athlon 64 has quadruple the number of bimodal counters in its global history counter, when compared to the Athlon XP.  All this technical jargon means that at similar clock speeds, even though it has a deeper pipeline, an Athlon 64 should outperform an Athlon XP in most circumstances.  Later on, you'll see we tested an Athlon XP 3200+, alongside the Athlon 64 FX-51, and with both processors clocked at 2.2GHz, the FX-51 was clearly a much faster chip.  AMD's efforts to increase the Athlon 64's IPC seems to have paid dividends nicely.


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