AMD and DDR2: The AM2 Athlon 64s

by John Reynolds



AMDWith the launch of the Athlon 64s in late 2003, AMD was able to firmly wrest the gaming performance crown away from Intel, though the aging Pentium 4 architecture’s hyper-threaded design still put up a tough scrap in media and multi-tasking chores. Yet with the introduction of dual-core processors last year, Intel could do little else but watch its desktop CPUs lose in virtually all key performance areas to its market rival’s offerings. And as Intel’s engineers futilely continued trying to find a way around what became a rather insurmountable thermal wall, AMD only widened the performance gap as the company continued releasing new Athlon 64 parts. Yet AMD has lagged behind Intel by several years with its lack of support for DDR2, a choice most likely based on the sensitivity of their Athlon 64’s integrated controllers to memory latencies. With the launch of the AM2 socket, however, AMD is bringing a wide lineup of desktop processors that support DDR2/667 and DDR2/800 to the market.

This article revolves around AMD’s two new high-end Athlon 64s, the FX-62 and the X2 5000+. The FX-62 has a clock rate of 2.8GHz, matching the previous fastest A64 frequency of the single-core FX-57. The X2 5000+ ships clocked at 2.6GHz. Both processors are manufactured using AMD’s 90nm Silicon on Insulator (SOI) process at their Dresden, Germany plant. Both parts also have 128KB of L1 cache per core, divided in half for instruction and data caches. Yet the FX-62 has a 1MB L2 cache per core compared to the 512KB of the more mainstream X2 parts. This results in a transistor count of roughly 227 million for the FX in contrast to the 153m for the X2s; which, coupled with the clock rate differences, gives the FX-62 a maximum output of 125W compared to the X2 5000+’s rating of 89W. Moreover, AMD has also announced a more energy-efficient desktop lineup that is rated at 65W, though these parts come with a slight price premium due to the chip binning required. Last, the AM2 line has a division in its DDR2 support in that the integrated memory controllers of single-core parts work with only DDR2/667 while all dual-core CPUs support DDR2/800.

As in the past, pricing on the new FX part breaks the $1,000 ceiling, with the FX-62 costing a svelte $1031 in quantities of 1,000. The rest of the mainstream desktop parts have the following price breakdown:

X2 5000+
X2 4800+
X2 4600+
X2 4400+
X2 4200+
X2 4000+
X2 3800+
Athlon 64 3800+
Athlon 64 3500+

Worth noting is the lack of a single-core CPU clocked similarly to the FX-57’s 2.8GHz, suggesting a strong emphasis from AMD on dual-core processors for the AM2 lineup. Including budget processors, it’s clear that AM2 is a major launch from top to bottom, leaving in question whether or not the company has plans for any future 939 CPUs.

One last quick point to address is that of memory clocks for all AM2 Athlon 64s. This has been made a recent ‘issue’ by Intel, which has insinuated that some frequency is being given up on the memory side due to AMD’s use of fixed dividers. The memory speed supported by the FX-62, for example, is obtained by multiplying the reference clock (200MHz), which is what issues the source signal that drives all components on the motherboard, by the multiplier (14) and then dividing by a whole number (7). For the FX-62 this results in 200 x 14 = 2800 (final clock speed of the CPU) divided by 7, giving a memory clock of 400MHz (a la DDR2/800). The X2 5000+, however, works out to be 200 x 13 (2600) divided by 7 and thus equating to a memory clock of 371MHz, which results in the 5000+ losing a small amount of memory bandwidth.

AMD’s review kit also included an NVIDIA nForce 590-based board, the ASUS M2N32-SLI Deluxe. NVIDIA in fact is supporting AM2 with an nForce 500 family of products, four new core logic chipsets geared toward different market segments and price ranges. The nForce 590 SLI-based board that AMD chose for their AM2 review kits is the top dog of this new family, boasting a whopping 49 PCI Express lanes (32 lanes just for the two PCIe slots). Worth noting, though, is that NVIDIA has decided to drop its hardware firewall for the entire nForce 500 lineup, possibly due to Windows Vista’s support for hardware-accelerated firewalls.

The FX-62 and X2 5000+ will be tested against AMD’s fastest 939 dual core, the FX-60, and the fastest Intel dual core SimHQ has available, the Pentium 4 955 (3.46GHz). Last, AMD claims that availability of all announced AM2 parts should be immediate upon launch May 23rd.

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