With its 6xx-series Pentium 4 processors, Intel has finally jumped on the desktop 64-bit bandwagon. Intel's EM64T architecture can implement Windows' x86-64 mode, and is also compatible with the AMD64 architecture. This means that you don't need different Windows operating systems to take advantage of 64-bit processing.

Intel's new processors offer some other innovations besides the 64-bit EM64T architecture. For example, all 6xx-series CPUs deliver 2MB of Level 2 cache -- double the amount on the 5xx-series chips. There's also improved power management in the shape of Enhanced Intel Speedstep Technology (EIST) and protection from malware infection via memory overflow thanks to the eXecute Disable (XD) bit.

The 6xx-series Pentium 4 chips have an 800MHz frontside bus (FSB) and are designed for use in standard desktop PCs. Intel is also offering a new Pentium 4 Extreme Edition clocked at 3.73GHz with a 1,066MHz FSB. This expensive ($999), high-end chip is only likely to appeal to a limited market -- mainly power users and gamers.

According to Intel, the 6xx-series Pentium 4s will replace the older line in the medium term. However, it may be some months before you can no longer buy 5xx-series chips.

6xx-series Pentium 4 processors
Processor	Clock speed	Level 2 cache	EM64T / XD / EIST	Price
Pentium 4 660	3.6GHz	2MB	yes / yes / yes	$605
Pentium 4 650	3.4GHz	2MB	yes / yes / yes	$401
Pentium 4 640	3.2GHz	2MB	yes / yes / yes	$273
Pentium 4 630	3.0GHz	2MB	yes / yes / yes	$224