AMD and Intel have already kicked the dual core revolution into high gear, but the overall market still needs to be properly defined, and all the product positions filled. This is still an emerging market, and the Athlon 64 X2 and Pentium D processors illustrate this quite clearly. Intel offers a lot of value in the Pentium D line, but the top-end 3.2 GHz clock speed is certainly not going to win any game benchmark awards. The Athlon 64 X2 has the clock speed and performance ends covered, but the high retail price certainly turned off some buyers. It was inevitable that one side would move into the other's niche, and it's hardly a surprise to see AMD offering a lower-priced addition to the Athlon 64 X2 line.
The Athlon 64 X2 line is comprised of two distinct architectures, and the Manchester and Toledo cores essentially provide dual Athlon 64 Venice or San Diego cores on a single processor. The Toledo core features a full 1MB of L2 cache per core, for a total of 2MB per processor, and X2 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 can handle both 32- and 64-bit code.
The Athlon 64 3800+ fits into the second part of the line, and is the Venice equivalent to the Athlon 64 X2 architecture. The L2 cache is cut in half to 512K, which means 1-MB total L2 per processor. The line includes the Athlon 64 X2 4600+ (2.4 GHz) and 4200+ (2.2 GHz), and represents the more mainstream portion of the AMD Athlon 64 X2 line. So it's only natural that the 2.0 GHz Athlon 64 X2 3800+ has found a home here, as this new processor is being targeted directly against the low-cost Pentium D line.
The Athlon 64 X2 processors are the first true dual core processors for the desktop, and compared to the Intel Pentium D/Pentium EE 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 that 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 determine overall 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 of the Athlon 64 X2 3800+ is similar to a standard AMD64 processor, and supports PC1600 to PC3200 memory in a dual-channel format, but the memory bus is different than in a true dual-processor system. There may be two cores on an X2 processor die, but there is only one HyperTransport link and therefore a single path to the system memory. 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, using all four DIMM sockets at DDR400 speeds, and improved memory mapping and lower latencies.
The Athlon 64 X2 3800+ is the latest addition to the AMD dual core line, and sports the 512K Manchester core running at a clock speed of 2.0 GHz. It is a 90nm SOI part, with a die size of 147mm2 and approximately 154 million transistors. Both of these specifications are much lower than a corresponding Toledo core, and as L2 cache sizes are equivalent, it naturally compares quite well against current 90nm San Diego cores. Core voltages are a bit lower at 1.30-1.40V, and the 89W thermal power rating of the Athlon 64 X2 3800+ has dropped down to that of a 90nm Athlon 64 4000+.
The Athlon 64 X2 3800+ is a Socket 939 part, and is fully compatible with existing platforms, although a BIOS update may be needed to properly ID the processor. Many of the other features are tied to the platform, and the Athlon 64 X2 3800+ uses a single HyperTransport link running at 2 GHz, and supports standard features such as Cool'n'Quiet. The low clock speed and decreased thermal power rating also means less stress on the platform and cooling hardware, both of which are main concerns when upgrading processors. On the upgrade front, we have noticed more vendors offering X2-compatible BIOS updates, and several of our nForce4, nForce3 and K8T800 Pro boards are now Athlon 64 X2 compliant.