The fierce competition between Intel and AMD has heated up the processor market, providing new choices for server systems, desktops, and laptops. With so many processors available, it's hard to understand the real differences between them. To help you sort through the options, here are the top 10 processors available today.

10. Intel Dual-Core Itanium 2—The Intel Dual-Core Itanium 2 was released in July. Unlike the other processors listed here, the Itanium 2 isn't binary compatible with today's 32-bit applications and is found only in high-end systems. The Itanium 2 uses 90nm technology. Models range from 1.4GHz to 1.6GHz and have from 6MB to 24MB of L3 cache and a 533MHz front-side bus. Maximum power consumption is 104 watts.

9. AMD Opteron—Opteron was the first processor to bring the x64 instruction set to market, enabling systems to run both native 32-bit and native 64-bit applications at full speed. AMD released the first dual-core Opteron in May 2005. The current Opterons use 90nm technology and have speeds ranging from 1.8GHz (at 55 watts) to 2.6GHz (at 92.6 watts).

8. Intel Xeon (EM64T)—The first dual-core Xeon with Intel Extended Memory 64 Technology (EM64T) shipped in October 2005. The current Xeons use new 65nm technology and a 1066MHz front-side bus. The top-of-the-line model runs at 3GHz, has a 4MB cache, and requires 80 watts of power. The low end of the 65nm line runs at 1.67GHz, has a 4MB cache, and requires 65 watts.

7AMD Sempron—The low end of AMD's processor line, older Semprons were 32-bit, but the newer ones are all x64 compatible. The main difference between the Sempron and the Athlon 64 is the Sempron's smaller 256KB L2 cache. The x64 Semprons run at 1.8GHz to 2GHz and at 62 watts of power, and use a Socket 754 motherboard.

6. Intel Pentium D—The newest versions of the Pentium D use 65nm technology, provide a 2MB cache, and come in models ranging from 62.8GHz (at 95 watts) to 3.7GHz (at 130 watts). The Pentium D uses a Socket Land Grid Array (LGA) 775 motherboard.

5. AMD Athlon 64 X2—AMD's first dual-core desktop processor, the Athlon 64 X2 is available in speeds from 2GHz to 2.6GHz with a 64KB L1 cache and a 1MB L2 cache per core. The 2GHz model consumes 35 watts, and the high-end model requires 89 watts. The Athlon 64 X2 uses 90nm technology. Earlier versions used a Socket 939 motherboard. The newest versions use the new Socket AM2.

4. Intel Core Solo—Intel Core Solo processors are single-core 32-bit CPUs used widely in laptops. The Solo uses 65nm process technology; speeds range from 1.06GHz (at 5.5 watts) to 1.83GHz (at 27 watts).

3. AMD Turion 64 X2—The Turion 64 X2 is a dualcore 64-bit processor designed for laptops. The current Turion X2 processors range from an entry-level CPU that runs at 1.6GHz (at 25 watts) to the 2.2GHz model with 2MB of L2 cache at 35 watts). The Turion 64 X2 uses 90nm technology and has a Socket S1 motherboard.

2. Intel Core 2 Duo—The Intel Core 2 Duo is the dual-core implementation of Intel's Core 2 processor line. The Duo CPUs use 65nm process technology and are primarily intended for laptops and desktops. The Duo CPUs range from 1.20GHz (at 9 watts) to 2.33GHz (at 31 watts). Intel plans to improve the Core 2 line in 2007 by implementing a quad-core design that puts two Core 2 dual-core CPUs in a single socket.

1. AMD 4x4—One of the most intriguing systems due out this year is the next-generation AMD Athlon processor, dubbed the 4x4. The AMD 4x4 platform consists of a two-socket motherboard in which each socket supports a dual-core CPU, giving the system four processing cores. A HyperTransport bus connects the two sockets to the system's I/O channels. AMD expects to release an 8X8 system using dual quad-core processors in 2007.