The Central Processing Unit
Every computer contains a central processing unit (CPU). The CPU of larger computers often spans several separate microprocessor chips and various circuit boards, whereas in a personal computer the CPU is a single chip. This microprocessor chip, also called an integrated circuit, is a small electronic device consisting of tiny transistors and other circuit parts on a piece of semiconductor material. This material is known as a semiconductor because it is neither a good conductor of electricity (like copper) nor a good insulator (such as rubber) Semiconductor material therefore does not interfere with the flow of electricity in a chip's circuits. The most commonly used semiconductor material is silicon, a type of purified glass.
On a personal computer, all processing functions are contained on a single microprocessor chip. Because the functions are housed on a single chip, the term CPU and microprocessor are used interchangeably. Recall from Chapter 1 that the CPU, or microprocessor, is often referred to as the "brain" of a personal computer system because it interprets and executes the instructions for most computer operations. The CPU consists of a control unit, an arithmetic logic unit (ALU) and registers,
These components of the CPU perform four basic operations that are collec tively called a machine cycle. The machine cycle includes fetching an instruction, decoding the instruction, executing the instruction, and storing the result. The machine cycle is the same whether you are using a midrange server or a personal computer/
Control Unit The control unit directs and coordinates the overall operation
of the computer system. It acts as a traffic officer, signaling to other parts of the computer system what they are to do. It interprets program instructions and thes initiates the action needed to carry them out. These are the fetching and decoding steps of the machine cycle. Fetching means retrieving an instruction or data from memory. Decoding means interpreting or translating the instruction into tricity (like copper) nor a good insulator (such as rubber) Semiconductor material therefore does not interfere with the flow of electricity in a chip's circuits. The most commonly used semiconductor material is silicon, a type of purified glass.
On a personal computer, all processing functions are contained on a single microprocessor chip. Because the functions are housed on a single chip, the term CPU and microprocessor are used interchangeably. Recall from Chapter 1 that the CPU, or microprocessor, is often referred to as the "brain" of a personal computer system because it interprets and executes the instructions for most computer operations. The CPU consists of a control unit, an arithmetic logic unit (ALU) and registers,
These components of the CPU perform four basic operations that are collectively called a machine cycle. The machine cycle includes fetching an instruction, decoding the instruction, executing the instruction, and storing the result. The machine cycle is the same whether you are using a midrange server or a personal computer/
Control Unit The control unit directs and coordinates the overall operation of the computer system. It acts as a traffic officer, signaling to other parts of the computer system what they are to do. It interprets program instructions and thes initiates the action needed to carry them out. These are the fetching and decoding steps of the machine cycle. Fetching means retrieving an instruction or data from memory. Decoding means interpreting or translating the instruction intological operations, such as comparing data items. For example, the ALU can deter mine if one data item, such as the number of hours an employee has worked, is less than equal to, or exceeds the number of hours in a standard 40-hour work week If the number of hours worked is less than or equal to 40, the employee's pay is calculated using a particular formula. If the hours worked exceeds 40, a different. formula is used for calculating overtime pay
Registers To speed up processing the ALU uses a register to temporarily hold instructions and data. This is the storing step of the machine cycle. Storing means writing or recording the result to memory. Registers are accessed much faster than memory locations outside the CPU. The time required to execute an instruc tion and store the result is called execution time, or E-time.
Various kinds of registers are used, each serving a specific purpose. Once processing begins, an Instruction register holds instructions currently being executed. A data register holds the data items being acted upon. A storage register holds the immediate and final results of processing
Coprocessors In addition to the main processor, or CPU, a personal computer
may also contain one or more coprocessors. A coprocessor is a special-purpose chip that assists the CPU in performing certain types of operations. The first mainstream coprocessor was a math coprocessor, which was used to perform mathematical computations more quickly for scientific, engineering, and statistical applications. Math coprocessors have now been integrated into most ALU compo- nents of microprocessor chips and are no longer separate chips. A graphics copro- cessor is designed specifically for handling image-intensive applications, such as Web pages and computer-aided design programs. A cryptographic coprocessor, also called a crypto-coprocessor, provides encryption and related processing