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. References: CompTIA IT Fundamentals+ Study Guide: Exam FC0-U61, Second Edition, Chapter 3: Computing Components, page 114.

A host firewall is a software program that controls the incoming and outgoing network traffic on a computer.
A host firewall can block or allow traffic based on rules that specify the source and destination addresses, ports, protocols, and applications. A host firewall can also monitor and log network activity for security purposes. A user can verify if a port is open or closed by checking the host firewall settings and rules on their PC. References: The Official CompTIA IT Fundamentals (ITF+) Student Guide (Exam FC0-U61), Chapter 5, Section 5.4, Page 230.

The type of memory that can retain its content after a system reboot is ROM. ROM stands for Read-Only Memory, which is a type of non-volatile memory that stores data permanently even when the power is turned off. ROM can only be read by the CPU, but not written or modified. ROM contains essential data and instructions that are needed for the system to boot up and operate, such as the BIOS (Basic Input/Output System) or the firmware. DDR is not the type of memory that can retain its content after a system reboot, but rather a type of RAM. RAM stands for Random Access Memory, which is a type of volatile memory that stores data temporarily while the computer is running. RAM allows fast access and modification of data by the CPU, but it loses its contents when the power is turned off. DDR stands for Double Data Rate, which is a technology that allows RAM to transfer data twice as fast as normal RAM. DDR has different generations, such as DDR2, DDR3, or DDR4, which have different speeds and capacities. DIMM is not the type of memory that can retain its content after a system reboot, but rather a type of module or package that contains RAM chips. DIMM stands for Dual In-line Memory Module, which is a circuit board that has RAM chips on both sides and pins on both edges. DIMM can be inserted into slots on the motherboard to increase the amount of RAM available for the system. DIMM has different types and sizes, such as SDRAM, DDR, DDR2, DDR3, or DDR4 DIMMs. RAM is not the type of memory that can retain its content after a system reboot, but rather the type of memory that loses its content when the power is turned off. RAM stands for Random Access Memory, which is a type of volatile memory that stores data temporarily while the computer is running. RAM allows fast access and modification of data by the CPU, but it loses its contents when the power is turned off. RAM can be packaged into modules or packages, such as DIMMs or SO-DIMMs. Reference: The Official CompTIA IT Fundamentals (ITF+) Student Guide (Exam FC0-U61), Chapter 1: IT Fundamentals1

Device Manager in Windows is a system utility used to view and control the hardware attached to the computer. It allows users to uninstall, disable, and update device drivers, as well as scan for hardware changes.
This utility is essential for managing the interactions between a computer's operating system and its hardware components.References: This functionality is outlined in various IT certification materials, including CompTIA's documentation which emphasizes understanding system utilities for effective IT support.