Introduction

The current desktop market reflects an increased awareness of dual core processors, and the advantages these offer to all levels of computer users. Basic desktop users enjoy unparalleled multi-tasking, media aficionados receive ultra high-end encoding performance, and even gamers get near top-end performance with the promise of multi-threaded games in the future. The Athlon 64 X2 line is at the forefront of dual core technology, and while we've covered off the Athlon 64 X2 4800+ and 3800+ in previous reviews, the Athlon 64 X2 4600+ and 4200+ processors offer a more compelling mix of high-end performance and feature a more mainstream pricing structure.

The Athlon 64 X2 Architecture

The Athlon 64 X2 line is comprised of two different core architectures, the Manchester and Toledo, which are essentially two Athlon 64 Venice or San Diego cores on a single dual core processor. The Manchester features 512K of L2 cache per core, or 1MB total for each processor, and available models include the 2.4 GHz 64 X2 4600+, 2.2 GHz 4200+ and 2.0 GHz 3800+. The Toledo core includes a full 1MB of L2 cache per core, for a total of 2MB per processor, and models include the 2.4 GHz Athlon 64 X2 4800+ and 2.2 GHz Athlon 64 X2 4400+. Each of the Athlon 64 X2 cores also features its own 64K of L1 instruction and 64K of L1 data cache, or 256KB of total L1 per processor. All Athlon 64 X2 processors support AMD64 and support both 32- and 64-bit code.

The Athlon 64 X2 processors are the first true dual core processors for the desktop, and compared to the current Intel Pentium D/Pentium EE 840 design, offer a more streamlined and forward-thinking architecture. The Athlon 64 X2 incorporates two cores onto a single die, but unlike Intel, provides a System Request Queue and Crossbar Switch onboard the processor itself. That means the two Athlon 64 X2 cores can communicate directly across a high-speed internal bus, rather than using the system bus like the Intel Smithfield dual core models. This can obviously speed up data and cache coherency transfers, as well as not relying on the platform or chipset to influence overall CPU performance levels or processor compatibility. This design is also far superior to Intel Hyper-Threading, where a single core emulates two logical processors.

The integrated memory controller on the Athlon 64 X2 4600+ and 4200+ is much the same as a standard AMD64 processor, and can handle PC1600 to PC3200 memory in a dual-channel format. Although there are two processor cores, there is only one HyperTransport link and only a single path to the system memory. This means the integrated memory controller is shared between the two cores, and memory bandwidth remains equivalent to current a single core Athlon 64 processor. The Athlon 64 X2 processors also receive all of the benefits of the 90nm Venice/San Diego revisions, including SSE3, the use of mismatched DIMMs on a memory channel, the ability to fill all four sockets at DDR400 speeds, and improved memory mapping and lower latencies.

The Athlon 64 X2 4600+ and 4200+ Processors

The current Athlon 64 X2 4600+ features a 90nm Manchester core running at 2.4 GHz, while the Athlon 64 X2 4200+ shares the same architecture, but runs at 2.2 GHz. Both are Socket 939 models, and are fully supported on most current AMD platforms, with usually only a BIOS update required to ID the new processor. The core voltage of 1.35V-1.4V also remains consistent through the Athlon 64 X2 line. The smaller Manchester core is now used with all Athlon 64 X2 4600+, 4200+ and 3800+ processors, and has a few definite advantages compared to the larger Toledo core.

Since the L2 cache has been physically reduced on the Manchester core, this drops the transistor count from a whopping 233 million, down to only 154 million. It also results in a smaller die size of 147mm2, compared to 199mm2 for the Toledo. You would think this would also reduce the thermal power requirement, but it remains unchanged at 110W for the Athlon 64 X2 4800+/4600+/4400+, while dropping to 89W for the 4200+. This lower thermal specification makes the Athlon 64 X2 4200+ an especially attractive upgrade option for existing AMD systems, as it means fewer potential cooling issues, and less stress on older platforms.