Ch 6: EVALUATING YOUR SYSTEM: UNDERSTANDING AND ASSESSING HARDWARE
EVALUATING YOUR CPU AND RAM
Cheat Sheet
A. The CPU Subsystem
1. CPU Basics: The central processing unit (CPU) processes instructions, performs calculations, manages the flow of information through the computer, and processes the data you input into information. The CPU is composed of the control unit and the arithmetic logic unit (ALU). The control unit coordinates the activities of all the computer components. The ALU performs all calculations and makes logic and comparison decisions. Every time the CPU performs a program instruction, it goes through a series of steps called the machine cycle.

2. CPU Speed and Location: Processor speed is measured in megahertz (MHz), or 1 million hertz, or gigahertz (GHz), or 1 billion hertz. The percentage of time that your CPU is working is referred to as CPU usage. The CPU is located on the motherboard.

3. Replacing a CPU: Replacement CPUs are expensive. Not all CPUs are interchangeable, and the replacement CPU must be compatible with the motherboard.

B. The RAM Subsystem
1. RAM Basics: RAM (random access memory) is the computer’s temporary storage space. RAM remembers everything that the computer needs to process data, but only while the computer is on. This means that RAM is volatile storage. When the power is off, the data stored in RAM is cleared out. Memory modules are the circuit boards that hold RAM chips. They fit into slots on the motherboard. RAM capacity is measured in megabytes (MB) or gigabytes (GB).

2. Physical Memory vs. Kernel Memory: The amount of RAM that is actually sitting on memory modules in your computer is your computer’s physical memory. The memory that your OS uses is called kernel memory. At a minimum, you need enough RAM to run the OS, run whatever applications you’re using, plus some additional RAM to hold the data you’re inputting.

3. Adding RAM: You need to be sure that you’re adding a compatible memory module to your computer. Every computer is designed with a maximum limit on the amount of RAM it can support. In addition, each computer is designed with a specific amount of slots on the memory board in which the memory cards fit, and each slot may have a limit on the amount of RAM it can support.

4. Virtual Memory: If you don’t have enough RAM to hold all the programs you’re trying to run, the OS stores the data that doesn’t fit in RAM into a space on the hard disk called virtual memory. When it is using virtual memory, your OS builds a page file on the hard drive to allow processing to continue. This enables the system to run more applications than can actually fit in its RAM. Adding RAM greatly affects system performance in this case.