The ProBook 640 supports a 1,600MHz processor memory clock speed which is faster than most portable PCs of this age and type. Most similar spec notebook PCs that were released more than two years ago support a 133MHz processor memory clock speed. In addition, this notebook PC supports 1 and 333MHz processor memory clock speeds.
A 1,600MHz processor memory clock speed is actually the best supported memory clock speeds supported by processor across all laptops of this age and type.
The worst supported memory clock speeds supported by processor amongst similar types of notebook PC is 133MHz.