Mobile Athlon XP

Mobile Athlon XPs (Athlon XP-M) are identical to normal Athlon XPs, apart from running at lower voltages, often lower bus speeds, and not being multiplier-locked. The lower V_core rating caused the CPU to have lower power consumption (ideal for battery-powered laptops) and lower heat production. Athlon XP-M CPUs also have a higher-rated heat tolerance, a requirement of the tight conditions within a notebook PC.

The Athlon XP-M replaced the older Mobile Athlon 4. The Mobile Athlon 4 used the older Palomino core, while the Athlon XP-M used the newer Thoroughbred and Barton cores. Some specialized low-power Athlon XP-Ms utilize the microPGA socket 563 rather than the standard Socket A.

The CPUs, like their mobile K6+ predecessors, were also capable of dynamic clock adjustment for power optimization. When the system is idle, the CPU clocks itself down through a lower bus multiplier and also reduces its voltage. Then, when a program demands more computational resources, the CPU very quickly (there is some latency) returns to intermediate or maximum speed to meet the demand. This technology was marketed as "PowerNow!". It was similar to Intel's SpeedStep power saving technique. The feature was controlled by the CPU, motherboard BIOS, and operating system. AMD later renamed the technology to Cool'n'Quiet, on their K8-based CPUs (Athlon 64, etc), and re-imagined it for use on desktop PCs as well.

Athlon XP-Ms were popular with desktop overclockers, as well as underclockers. The lower voltage requirement and higher heat rating resulted in CPUs that were basically "cherry picked" from the manufacturing line. Being the best of the cores off the line, the CPUs typically were more reliably overclocked than their desktop-headed counterparts. Also, the fact that they weren't locked to a single multiplier was a significant simplification for the overclocking process. Some Barton core Athlon XP-Ms have been successfully overclocked to as high as 3.1 GHz.

As stated, the chips were also liked for their underclocking ability. Underclocking is a process of determining the lowest V_core at which a CPU can remain stable at for a given clock speed. The Athlon XP-M CPUs were capable of running lower voltages per clock rate compared to their desktop siblings. As such, the chips were used in home theater PC systems due to their high performance and low heat output at low V_core settings.