I am controlling my CNC with Mach3 on an old IBM Thinkpad laptop (Pentium 1.8 GHz, 512 MB RAM) with a parallel port.

I made a fresh Windows XP install skipping the ACPI (Advanced Configuration and Power Interface) install by holding F5 (select standard pc) or simply F7 during install, when at the bottom of the screen is asking to press F6 if you have raid devices. This way there will be no APM/ACPI installed. APM/ACPI is responsible for reducing the parallel port clock speed to reduce power consumption, and there is no other way to disable this function.

Without the APM/ACPI the laptop runs at full power but there is no cooling problem because the cooling system relies on temerature sensors not software. There is no battery monitor, windows does not know/inform you if you are running on AC or battery or the battery level, but who cares as long as the laptop is always plugged in. The only downside, very annoying at the beginning (now I'm used to it), is that the system is not shutting down automatically. You get a message "It is now safe to turn off your computer" and need to press the power button for two seconds to cut the power.

I think the most important thing is to have a computer dedicated to control the CNC. With a fresh windows installed, any graphics enhancements disabled, and only the CNC control software installed (Mach3 or other).

This way I get excellent results even at 100 KHz with the Mach3 timer variations test software on my old IBM Thinkpad laptop.