Processor speed is measured in hertz (Hz), which is the number of cycles per second that the processor can perform. The higher the processor speed, the faster the processor can execute instructions. Gigahertz (GHz) is equal to one billion hertz, while megahertz (MHz) is equal to one million hertz. Megabits per second (Mbps) and gigabits per second (Gbps) are units of data transfer rate, not processor speed. Therefore, 3.6GHz would indicate the fastest processor speed among the options given. Reference: CompTIA IT Fundamentals+ Study Guide: Exam FC0-U61, Second Edition, Chapter 3: Computing Components, page 114.