Unit 1 Hardware Basics

1.1 Central Processing Unit

1.1.1 Text

The hardware of a digital computer system is divided into four functional sections. The block diagram of Fig. 1-1 shows the four basic units of simplified computer: the input unit, central processing unit (CPU), memory unit, and output unit. Each section has a special function in terms of overall computer operation.

The CPU is the heart of the computer system. It is responsible for performing all arithmetic operations and logic decisions initiated by the program. In addition to arithmetic and logic functions, the CPU controls overall system operation.

The input and output units are the means by which the CPU communicates with the outside world. The input unit is used to input information and commands to the CPU for processing. For instance, a keyboard can be used to input a new program. After processing, the information results must be output. This output of data from the system is performed under control of the output unit. The memory unit of the computer is used to store information such as numbers, names and addresses. In the computer system, memory is divided into two different sections, known as main storage and auxiliary storage.

A computer can solve series of problems and make hundreds, even thousands of logical decisions without becoming tired or bored. It can find the solution to a problem in a fraction of the time, it takes a human being to do the job. A computer can replace human beings in dull and routine tasks, but it has no originality; it works according to the instructions given to it and cannot exercise any value judgements. But a computer can carry out vast numbers of arithmetic logical operations almost instantaneously.

The CPU in a microcomputer is actually the one relatively small integrated circuit or chip. Although most CPU chips are smaller than a lens of a pair of glasses, the electronic components they contain would have filled a room a few decades ago. Using advanced microelectronic techniques,manufacturers can cram tens of thousands of circuits into tiny layered silicon chips that work dependably and use less power. The CPU coordinates all the activities of the various components of the computer. It determines which operations should be carried out, and what is the order. The CPU can also retrieve information from memory and can store the results of manipulations back into the memory unit for later reference.

The basic job of computers is the processing of information. For this reason, computers can defined as devices which accept information in the form of instructions called a program and characters called data, perform mathematical and logical operations on the information, and then supply results of these operations. The program, which tells the computers what to do and the data, which provide the information needed to solve the problem, are kept inside the computer in a place called memory.

Computers are thought to have many remarkable powers. However, most computers, whether large or small, have three basic capabilities.

First, computers have circuits for performing arithmetic operations, such as addition, subtraction, division, multiplication and exponentiation.

Second, computers have a means of communicating with the user. After all, if we couldn’t feed information in and get results back, these machines would not be of much use.

Third, computers have circuits which can make decisions. The kinds of decisions which computer circuits can make are of the type: Is one number less than another? Are two numbers equal? And, is one number greater than another?

A CPU can be a single microprocessor chip, a set of chips, or a box of boards of transistors, chips, wires, and connectors. Differences in CPUs distinguish mainframes, mini-computers and micro-computers. A processor is composed of two functional units: a control unit and an arithmetic/logic unit, and a set of special workspaces called registers.

The control unit

The control unit is the functional unit that is responsible for supervising the operation of the entire computer system. In some ways, it is analogous to a telephone switchboard with intelligence because it makes the connections between various functional units of the computer system and calls into operation each unit that is required by the program currently in operation. The control unit fetches instructions from memory and determines their type or decodes them. It then breaks each instruction into a series of simple small steps or actions. By doing this, it controls the step-by-step operation of the entire computer system.

The Arithmetic/Logic Unit

The Arithmetic/Logic Unit (ALU) is the functional unit that provides the computer with logical and computational capabilities. Data are brought into the ALU by the control unit, and the ALU performs whatever arithmetic or logic operations are required to help carrying out the instructions. Arithmetic operations include adding, subtracting, multiplying, and dividing. Logic operations make a comparison and take action based on the results. For example, two numbers might be compared to determine if they are not equal. If they are equal, processing will continue; if they are not equal, processing will stop.

Registers

A register is a storage location inside the processor. Registers in the control unit are used to keep track of the overall status of the program that is running. Control unit registers store information such as the current instruction, the location of the next instruction to be executed, and the operands of the instruction. In the ALU, registers store data items that are added, subtracted, multiplied, divided, and compared. Other registers store the results of arithmetic and logic operations.

Instruction

An instruction is made up of operations that specify the function to be performed and operands that represent the data to be operated on. For example, if an instruction is to perform the operation of adding two numbers, it must know what the two numbers are and where the two numbers are. When the numbers are stored in the computer’s memory, they have an address to indicate where they are, so if an operand refers to data in the computer’s memory, it is called an address. The processor’s job is to retrieve instructions and operands from memory and to perform each operation. Having done that, it signals memory to send it to the next instruction.

The CPU executes each instruction in a series of small steps:

1.Fetch the next instruction from memory into the instruction register.

2.Change the program counter to point to the following instruction.

3.Determine the type of instruction just fetched.

4.If the instruction uses data in memory, determine where they are.

5.Fetch the data into internal CPU registers.

6.Execute the instruction.

7.Store the results in the proper place.

Go to step 1 to begin executing the following instruction.

This sequence of steps is frequently referred to as the fetch-decode-execute cycle. It is central to the operation of all computers. This step-by-step operation is repeated over and again at awesome speed. A timer called a clock releases precisely timed electrical signals that provide a regular pulse for the processor’s work. The term that is used to measure the computer’s speed is borrowed from the domain of electrical engineering and is called a megahertz (MHz) which means million cycles per second.

Key Words

address 地址，寻址

analogous 类似的，相似的

arithmetic 算术的

auxiliary 辅助的，补充的

awesome 惊人的，令人敬畏的

capability 性能，能力

decode 解码，译码

distinguish 区别，辨别

exponentiation 幂运算

fetch 获取，取得

fraction 小部分

initiate 开始，启发，提议，创始

instantaneously 瞬间地，即时地

instruction 指令

keyboard 键盘

mainframe 大型机

manipulation 操作，处理

microelectronic 微电子的

operand 操作数

originality 创意，创造力

retrieve 恢复

remarkable 显著的，不平常的

sequence 顺序，序列

silicon 硅

transistor 晶体管

1.1.2 Exercises

1.Translate the following phrases into English

（1）集成电路

（2）取指—译码—执行

（3）算术逻辑运算

（4）微电子技术

（5）数字计算机系统

（6）辅助存储器

（7）工作区

（8）逻辑决策

2.Translate the following phrases into Chinese

（1）Central Processing Unit

（2）functional unit

（3）current instruction

（4）instruction register

（5）program counter

（6）electronic components

（7）input information and commands

（8）Arithmetic/Logic Unit

3.Identify the following to be True or False according to the text

（1）A computer can replace people to do all kinds of work.

（2）In the ALU, registers store data items that are added, subtracted, multiplied, divided, and compared.

（3）Registers in the control unit are used to keep track of the overall status of the program.

（4）In the ALU, registers only store the results of arithmetic and logic operations.

（5）A register is a storage location inside the processor.

（6）ALU fetched instructions from memory and determines their type.

（7）To store the results in the proper place is done by ALU.

（8）The term that is used to measure the computer’s speed is borrowed from the domain of electrical engineering.

4.Reading Comprehension

（1）A processor is composed of two functional units, they are_________________.

a.an arithmetic/logic unit and a storage unit

b.a control unit and some registers

c.a control unit and an arithmetic/logic unit

d.some registers and an arithmetic/logic unit

（2）The control unit fetches ________________from memory and decodes them.

a.data

b.information

c.results

d.instructions

（3）_______________ is a storage location inside the processor.

a.A register

b.ALU

c.Control unit

d.Memory

（4）The CPU executes each instruction in a series of steps, the sequence is_____________.

a.execute-fetch-decode

b.fetch-decode-execute

c.decode-execute-fetch

d.fetch-execute-storage

1.1.3 Reading Material

Microprocessor

Microcomputer, or micro for short, is a kind of computer. It was born in the early 1970s. The computer’s brain is called the microprocessor. That’s the main chip in a computer that does all the work. It’s also the center of activity on the motherboard. It interprets and executes the instructions which comprise a computer program. The CPU consists of an arithmetic unit and its associated circuitry, known as the arithmetic and logic unit, and an instruction counter and decoder. The CPU can perform only one operation at a time. Essentially, numerically coded instructions are stored in the computer’s high-speed storage, or primary storage. The CPU takes the instructions one at a time and executes them. The numerical coding of the instruction tells the CPU which operation to perform and where the data upon which the operation is to take place is stored.

The central processor of the micro, called the microprocessor, is built as a single semiconductor device; that is, the thousands of individual circuit elements necessary to perform all the logical and arithmetic functions of a computer are manufactured as a single chip. A complete microcomputer system is composed of a microprocessor, a memory and some peripheral equipment. The processor, memory and electronic controls for the peripheral equipment are usually put together on a single or on a few printed circuit boards. Systems using microprocessors can be hooked up together to do the works that until recently only minicomputer systems were capable of doing. Micros generally have somewhat simpler and less flexible instruction sets than minis, and are typically much slower. Similarly, minis are available with much larger primary memory sizes. Micros are becoming more powerful and converging with minicomputer technology.

The microprocessor is essentially a small calculator. It does basic calculator like things—adding, subtracting, multiplying, and dividing values stored in the computer’s memory. Computer programs tell the microprocessor what to do, which is how everything works inside a PC.

Other terms for the microprocessor include the processor, the central processing unit (CPU), and the number of the microprocessor, such as 8088, 80286, 80386,80486, and so on. (Note that although there are many numbers/names for a microprocessor, those above are the most common.)There are three main varieties of microprocessors for PCs: the 8088/8086, the 80286, or AT microprocessor , and the 386 family of microprocessor . There is no 586 microprocessor. Instead of calling it a number, the company that manufactured it(Intel)called it the Pentium. It’s the micro part of microprocessor that led old-time computer users to call PCs microprocessor. This may have applied to the first microprocessor, but today’s powerhouse PCs are anything but micro.

How can you tell which microprocessor your PC has? The best way is to look at the label, which probably has a microprocessor number in it: 386 and 486 are common. And, as a last resort, you can use PC diagnostic software to figure out which microprocessor you have. The latest offspring in the 386 families are the Pentium computers, which would have been called 586 computers. The Pentium is basically a fast, all-powerful 386. About a year after the first Pentium microprocessor came out, a small problem was discovered, the Pentium had a problem doing math. Specifically, a division problem, when two particular numbers were divided, the Pentium produced a result that wasn’t quite accurate. Intel quickly admitted to the mistake and offered replacement Pentiums. Then they fixed the problem and any new Pentiums that came rolling out of the factory were doing much better in math. Now there’s nothing more to worry about.