AMD had been the first manufacturer to demonstrate a working dual-core processor design in the summer of 2004, so it came as something of a surprise when rival Intel brought the first dual-core processor to market in the spring of 2005. However, not only was AMD 64 X2 only a short time behind Intel’s Pentium Extreme Edition and Pentium D CPUs in terms of release dates, but it was significantly ahead in terms of performance.

The Athlon 64 XP includes all the features seen on single-core Athlon 64 designs, such as HyperTransport technology and Enhanced Virus Protection (EVP). When used with Windows XP SP2, EVP sets portions of system memory aside as data only, so that any code resident in these areas may only be read from or written to, not executed. In this way, EVP acts as a preventative measure against common malicious viruses, causing the virus to be localised, short-lived and non-contagious, and eventually being flushed from system memory.

Carrying the designation X2, the new range extends AMD’s existing model naming convention. At the time of its release, the X2 picked-up from fastest single-core part at the time, the 4000+. The original range comprised the 4200+. 4400+, 4600+ and the top-end 4800+. Dual-core chips run slower than single-core for some processes, making comparisons difficult. However, AMD claims an 80% performance hike for the X2 compared with a single-core of the same frequency when running on processor-intensive digital media software applications.

The basic architecture and specification per core of the X2 is essentially the same as existing Athlon 64 designs. The difference is that the new chips – made of a single 199mm2 die, each comprising more than 233 million transistors – are fabricated on AMD’s 90nm process technology. The degree of integration of the dual cores is greater than with Intel’s design, the two AMD cores being capable of communicating directly without use of the external motherboard chipset and actually sharing a single integrated memory controller.

Thus, the specifications of the originally announced range of Athlon 64 X2s were equivalent to those of the existing 3500+, 3700+, 3800+ and 4000+ parts, with varying levels of L2 cache and clock speed. The models with 512KB of cache per core are based on the Manchester dual core while the versions with while the 1MB L2 cache versions use the Toledo design. While still within the design envelope of current Athlon 64 motherboards, the power consumption of the Toledo versions is higher, up to a maximum 110 watts.

By the summer of 2005, the range had been extended with the addition of a new low-end 3800+ chip:

Model Number Frequency L2 Cache (per core)
4800+ 2.4 GHz 1MB
4600+ 2.4 GHz 512KB
4400+ 2.2 GHz 1MB
4200+ 2.2 GHz 512KB
3800+ 2.0 GHz 512KB

Aside from speed, the other significant advantage AMD’s design has over Intel dual-core processors is compatibility and, consequently, upgradeability. Whereas the Intel CPUs require new chipsets and VRMs to cope with increased power consumption, by reducing the voltage per core slightly from 1.50V to 1.35V, AMD has been able to design the dual-core chip to fit the same 939-pin form factor as single-core processors, making it compatible with existing Athlon 64 90nm-ready motherboards, with only a BIOS update being required.

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