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SNHU - IT-201 Computer Platform Technologies
Written by: Chris Bell - September, 2012

CPU Hardware and Processing

1. What are the three primary components of a CPU? What is the function of each component?

Arithmetic Logic Unit (ALU): Performs all of the adding, subtracting, multiplying and dividing. It also performs logic operations that result in True or False. The ALU loads data from registers and the external control unit tells the ALU what operation to perform on the data.

Control Unit: It's responsible for executing or storing results from the ALU. It fetches the data, performs a function that it’s told, executes and possibly stores the finished data.

Registers: These are responsible for temporarily storing data for the processor. The control unit tells it to hold, accept or send certain data and it performs the function accordingly.

2. How does a CPU process an instruction? How can instructions be combined to form a complex processor operation?

First, the control unit fetches the instruction, decodes it and stores it in a register. Then it's sent to the ALU to be executed and stored again. Then external communication can pull it from memory when needed. Complex processor operations can be performed but must first be translated into simple arithmetic. It can process A - B or A + (-B).

3. What are the similarities and differences of RISC and CISC?

Reduced Instruction Set Computing avoids anything complex, anything with data transformation and most data movement. It executes the simple arithmetic and data transfers.

Complex Instruction Set Computing handles the complex arithmetic with more memory, more processing power with less registers. It saves 4 processing cycles during each operation. The problem with complex computing is that it requires a lot of fetching and time to execute when there aren't that many complex instructions used on a typical PC day to day.

4. What is the most important difference between primary and secondary storage? How does this difference affect the CPU's performance?

The main difference is speed. Fetching from primary storage is typically 100,000 times faster than secondary storage and their registers have a zero wait state. The primary storage is considered volatile however, which means it can lose data over long periods of time. Secondary storage is considered to be nonvolatile.

5. What is the purpose of a memory storage hierarchy?

The memory storage hierarchy defines the most wanted pieces of the CPU. When increasing memory it will have to suffer in other areas such as cost or speed. The hierarchy defines where each user might be depending on the areas they see as more important. If someone is looking for speed, but has no need for memory, the costs can be put more towards the speed.

References: (2012). What Are Primary and Secondary Storage Devices? Retrieved from: (August, 2008). The Basic Functions of a Computer. Retrieved from: