计算机专业英语论文--硬件概述

题目：计算机硬件概述（Overview of the computer hardware based）

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A computer is a fast and accurate symbol processing system. It can accept, store, process data and produce output results. A computer can automatically process data without human intervention. However, it must be given a set of instruction to guide it, step by step, through processes. The set of instructions is called a program, The program is stored physically inside the machine, making it a program.

All computer systems of interest to us are similar. They contain hardware components for input, central processing unit and output. The system on the small-scale is called a microcomputer or minicomputer. Continuing up the size scale, the mainframe computer is one that may offer a faster processing speed and a greater storage capacity than a typical mini. Finally comes the supercomputer, designed to process complex scientific applications，which is the largest and fastest.

Although the capacity of computers' storage locations is varied，every computer stores numbers，letters，and other characters in a coded form. Every character in the storage is represented by a string of 0s and 1s，the only digits founded in the binary numbering system. BCD and ASCII are popular computer codes.

So, what part of computer hardware that contains it? Computer hardware has four parts: the central processing unit (CPU) and memory, storage hardware, input hardware, and output hardware.

The Central Processing Unit

Pronounced as separate letters it is the abbreviation for central processing unit. The CPU is the brains of the computer. Sometimes referred to simply as the central processor, but more commonly called processor, the CPU

is where most calculations take place. In terms of computing power, the CPU is the most important element of a computer system.

On large machines, CPUs require one or more printed circuit boards. On personal computers and small workstations, the CPU is housed in a single chip called a microprocessor. Since the 1970's the microprocessor class of CPUs has almost completely overtaken all other CPU implementations.

Early CPUs were custom-designed as a part of a larger, sometimes one-of-a-kind, computer. However, this costly method of designing custom CPUs for a particular application has largely given way to the development of mass-produced processors that are made for one or many purposes. This standardization trend generally began in the era of discrete transistor mainframes and minicomputers and has rapidly accelerated with the popularization of the integrated circuit (IC). The IC has allowed increasingly complex CPUs to be designed and manufactured to tolerances on the order of nanometers. Both the miniaturization and standardization of CPUs have increased the presence of these digital devices in modern life far beyond the limited application of dedicated computing machines. Modern microprocessors appear in everything from automobiles to cell phones and children's toys.

The CPU itself is an internal component of the computer. Modern CPUs are small and square and contain multiple metallic connectors or pins on the underside. The CPU is inserted directly into a CPU socket, pin side down, on the motherboard. Each motherboard will support only a specific type or range of CPU so you must check the motherboard manufacturer's specifications before attempting to replace or upgrade a CPU. Modern CPUs also have an attached heat sink and small fan that go directly on top of the CPU to help dissipate heat.

Two typical components of a CPU are the following:

The arithmetic logic unit (ALU), which performs arithmetic and logical operations.

The control unit (CU), which extracts instructions from memory and decodes and executes them, calling on the ALU when necessary.

To properly perform its job, the CPU must complete a cycle of four steps. The first step in this cycle is to fetch a instruction from a software program's memory. Once the CPU fetches the instruction, its second step is to decode the instruction. By decoding the instruction, the CPU is able to organize the

information from the instruction in a manner that allows the CPU to complete the next step, which is executing.

During the execution step, the CPU completes the instruction. It accomplishes this by following the information gained during the decoding step. Once the CPU has finished executing the instruction, the final step in this cycle is to write-back the results that occurred during the execution step. The CPU can write-back the results to its own internal register, or to the main memory of the computer.

The Control Unit: A control unit is one of the two components of the central processing unit. The function of the control unit is to extract information which is stored in the memory and to decode and execute those instructions.

It also takes help from the arithmetic logic unit , whenever required. The control unit is very important for computers functioning . The control unit has outputs which take charge of the activities of the entire device. Some regard the control unit to be an FSM or finite state machine which is used for hardware and software applications.

Control Unit and Microprogram :There was a time when the manufacturing of control units was a difficult process, especially in designing it. But today the scenario has changed. A control unit is executed in the form of microprograms which remain in control stores. There is a micro sequencer which chooses the words and certain portions of those words which directly manage the various computer parts. These parts are arithmetic and logic units, buses, instruction registers, registers and input/output. Today the latest computers may possess subsidiary controllers for every subsystem, which would be supervised by the main control unit .

Functions of Control Unit:A control unit can be described as a sort of circuitry that supervises and controls the path of information that runs over the processor and organizes the various activities of those units that lie inside it.

It carries out many tasks such as decoding, fetching, handling the execution and finally storing the results.

It controls the execution of instructions in a sequential order.

It guides the flow of data through the different parts of the computer.

It interprets the instructions.

It regulates the time controls of the processor.

It sends and receives control signals from various peripheral devices.

A control unit is a major computer part which helps in the functioning of the central processing unit and in turn runs the whole computer.

The Arithmetic-Logic Unit: An arithmetic-logic unit (ALU) is the part of a computer processor ( CPU ) that carries out arithmetic and logic operations on the operand s in computer instruction word s. In some processors, the ALU is divided into two units, an arithmetic unit (AU) and a logic unit (LU). Some processors contain more than one AU - for example, one for fixed-point operations and another for floating-point operations. (In personal computers floating point operations are sometimes done by a floating point unit on a separate chip called a numeric coprocessor.)

Typically, the ALU has direct input and output access to the processor controller, main memory (random access memory or RAM in a personal computer), and input/output devices. Inputs and outputs flow along an electronic path that is called a bus . The input consists of an instruction word (sometimes called a machine instruction word) that contains an operation code (sometimes called an "op code"), one or more operands, and sometimes a format code. The operation code tells the ALU what operation to perform and the operands are used in the operation. (For example, two operands might be added together or compared logically.) The format may be combined with the op code and tells, for example, whether this is a fixed-point or a floating-point instruction. The output consists of a result that is placed in a storage register and settings that indicate whether the operation was performed successfully. (If it isn't, some sort of status will be stored in a permanent place that is sometimes called the machine status word.)

In general, the ALU includes storage places for input operands, operands that are being added, the accumulated result (stored in an accumulator ), and shifted results. The flow of bits and the operations performed on them in the subunits of the ALU is controlled by gated circuits. The gates in these circuits are controlled by a sequence logic unit that uses a particular algorithm or sequence for each operation code. In the arithmetic unit, multiplication and division are done by a series of adding or subtracting and shifting operations. There are several ways to represent negative numbers. In the logic unit, one of 16 possible logic operations can be performed - such as comparing two

operands and identifying where bits don't match.

The design of the ALU is obviously a critical part of the processor and new approaches to speeding up instruction handling are continually being developed.

Memory

In computing , memory refers to the state information of a computing system, as it is kept active in some physical structure. The term "memory" is used for the information in physical systems which are fast (ie RAM ), as a distinction from physical systems which are slow to access (ie data storage ). By design, the term "memory" refers to temporary state devices, whereas the term "storage" is reserved for permanent data. Advances in storage technology have blurred the distinction a bit —memory kept on what is conventionally a storage system is called " virtual memory ".

Colloquially, computer memory refers to the physical devices used to store data or programs (sequences of instructions) on a temporary or permanent basis for use in an electronic digital computer . Computers represent information in binary code , written as sequences of 0s and 1s. Each binary digit (or "bit") may be stored by any physical system that can be in either of two stable states, to represent 0 and 1. Such a system is called bistable. This could be an on-off switch, an electrical capacitor that can store or lose a charge, a magnet with its polarity up or down, or a surface that can have a pit or not. Today, capacitors and transistors, functioning as tiny electrical switches, are used for temporary storage, and either disks or tape with a magnetic coating, or plastic discs with patterns of pits are used for long-term storage.

Computer memory is usually meant to refer to the semiconductor technology that is used to store information in electronic devices. Current primary computer memory makes use of integrated circuits consisting of silicon -based transistors . There are two main types of memory: volatile and non-volatile .

Storage Hardware

The purpose of storage hardware is to provide a means of storing computer instruction and data in a form that is relatively permanent, that is, the data is not lost when the power is turned off—and easy to retrieve when needed for processing . There are four kinds of storage hardware: floppy disks, hard disks, optical disk, and magnetic tape.

Floppy Disks: A soft magnetic disk. It is called floppy because it flops if

you wave it (at least, the 5??-inch variety does). Unlike most hard disks, floppy disks (often called floppies or diskettes) are portable, because you can remove them from a disk drive. Disk drives for floppy disks are called floppy drives. Floppy disks are slower to access than hard disks and have less storage capacity, but they are much less expensive. And most importantly, they are portable.

Floppies come in three basic sizes:

8-inch: The first floppy disk design, invented by IBM in the late 1960s and used in the early 1970s as first a read-only format and then as a read-write format. The typical desktop/laptop computer does not use the 8-inch floppy disk.

5.25-inch: The common size for PCs made before 1987 and the predecessor to the 8-inch floppy disk. This type of floppy is generally capable of storing between 100K and 1.2MB (megabytes) of data. The most common sizes are 360K and 1.2MB.

3.5-inch: Floppy is something of a misnomer for these disks, as they are encased in a rigid envelope. Despite their small size, microfloppies have a larger storage capacity than their cousins -- from 400K to 1.4MB of data. The most common sizes for PCs are 720K (double-density) and 1.44MB (high-density). Macintoshes support disks of 400K, 800K, and 1.2MB.

Hard Disks: In any computer system the hard disk is considered as the secondary memory device that is used for the primary data storage. The primary memory is obviously the RAM. But as the RAM is the primary memory it cannot be used for the purpose of the permanent data storage. Hence a secondary memory device is necessarily needed for the purpose of the data storage in any computer system. Apart from hard disk drive the tape storage media can also be used as the secondary storage device. But the hard disk drive is the most popularly used secondary memory device. The main reason for this is the access speed and the reliability of the data it can offer. In the case of the tape drives the access speed is much low and the data transfer is comparatively low than the hard disk drive.

Since the primary memory that is the RAM is a non volatile memory hence it cannot be used as the permanent memory storage device. Hence the hard disk or the need for as a secondary memory device is needed in any computer. The primary function of the primary memory is to load the programs so that the CPU – Central Processing Unit can easily and speedily access and execute the instructions. The primary memory can only boot the computer system; but it the hard disk drive that is responsible for the loading and the proper functioning of any operating system. The operating system is a necessary for the computers to run to the expectations of the user. Hence the hard disk is a must for the loading of the hard disk drive. The importance of the primary memory is that it is a compulsion that is necessary for the start up of the

computer. A computer can start up even with out a hard disk. But since there is no operating system that is present in the computer hence it is not possible to load the operating system. The computer will display a message usually in such a situation stating that ―Disk Boot Failure‖.

The information that is required to boot a computer is stored in the hard disk boot sector. Also the importance of the hard disk drive is to store the backup of the data or any information that is created by the user. Apart from the hard disk drives the other storage devices like the optical disks that are the CD ROM, DVD ROM etc can be used for the purpose of the backup of the data or user information. The floppy disks can also be used for the backup of the data. The hard disk specification should also match the expectations of the computers; that is the storage capacity and access speed.

The internal organization of the any hard disk drive consists of the following four parts primarily. They are as listed below: the Platters, the Head Arm, the Chassis, and also the Head Actuator. The hard disk drives are also available in two different types that is the internal and also the external hard disk drives. The internal hard disk drives are used for the storage of the data in the computer case. There are not portable and usually are inside the case. The external hard disk drives are portable can be connected to other computer systems as well. There is a hard casing over the hard disk.

Optical Disks: In computing and optical recording , an optical disc is a flat, usually circular disc which encodes binary data in the form of pits (binary value of 0 or off, due to lack of reflection when read) and lands (binary value of 1 or on, due to a reflection when read) on a special material (often aluminium ) on one of its flat surfaces. The encoding material sits atop a thicker substrate (usually polycarbonate ) which makes up the bulk of the disc and forms a dust defocusing layer. The encoding pattern follows a continuous, spiral path covering the entire disc surface and extending from the innermost track to the outermost track. The data is stored on the disc with a laser or stamping machine, and can be accessed when the data path is illuminated with a laser diode in an optical disc drive which spins the disc at speeds of about 200 RPM up to 4000 rpm or more depending on the drive type, disc format, and the distance of the read head from the center of the disc (inner tracks are read at a faster disc speed). The pits or bumps distort the reflected laser light, hence most optical discs (except the black discs of the original PlayStation video game console ) characteristically have an iridescent appearance created by the grooves of the reflective layer. The reverse side of an optical disc usually has a printed label, generally made of paper but sometimes printed or stamped onto the disc itself. This side of the disc contains the actual data and is typically coated with a transparent material, usually lacquer . Unlike the 3?-inch floppy disk , most optical discs do not have an integrated protective casing and are

therefore susceptible to data transfer problems due to scratches, fingerprints, and other environmental problems.

Optical discs are usually between 7.6 and 30 cm (3 to 12 in) in diameter, with 12 cm (4.75 in) being the most common size. A typical disc is about 1.2 mm (0.05 in) thick, while the track pitch (distance from the center of one track to the center of the next) is typically 1.6 μm .

An optical disc is designed to support one of three recording types: read-only (eg: CD and CD-ROM ), recordable (write-once, eg CD-R ), or re-recordable (rewritable, eg CD-RW ). Write-once optical discs commonly have an organic dye recording layer between the substrate and the reflective layer. Rewritable discs typically contain an alloy recording layer composed of a phase change material, most often AgInSbTe , an alloy of silver , indium , antimony and tellurium.

Optical discs are most commonly used for storing music (eg for use in a CD player ), video (eg for use in a DVD player ), or data and programs for personal computers . The Optical Storage Technology Association (OSTA) promotes standardized optical storage formats. Although optical discs are more durable than earlier audio-visual and data storage formats, they are susceptible to environmental and daily-use damage. Libraries and archives enact optical media preservation procedures to ensure continued usability in the computer's optical disc drive or corresponding disc player.

For computer data backup and physical data transfer, optical discs such as CDs and DVDs are gradually being replaced with faster, smaller, and more reliable solid state devices, especially the USB flash drive . This trend is expected to continue as USB flash drives continue to increase in capacity and drop in price. Similarly, personal portable CD players have been supplanted by portable solid state MP3 players , and MP3 music purchased or shared over the internet has significantly reduced the number of audio CDs sold annually.

Magnetic Tape: Magnetic tape is an effective way of making a backup, or duplicate, copy of your programs and data. We mentioned the alarming consequences that can happen if a hard disk suffers a head crash. You will lose some or all of your data or programs. Of course, you can always make copies of your hard-disk files on floppy disks. However, this can be time-consuming and may require many floppy disks. Magnetic tape is sequential access storage and can solve the problem mentioned above.

Input Hardware: Input devices take data and programs people can read or understand and convert them to a form the computer can process. This is the machine-readable electronic signals of 0s and 1s. Input hardware is of two kinds: Keyboard entry and direct entry.

Keyboard Entry: Data is input to the computer through a keyboard that looks like a typewriter keyboard but has additional keys. In this method, the user typically reads from an original document called the source document.

The user enters that document by typing on the keyboard.

Direct Entry: Data is made into machine-readable form as it is entered into the computer, no keyboard is used. Direct entry devices may be categorized into three areas: pointing devices (for example, mouse, touch screen, light pen, digitizer, they are all pointing devices), scanning devices (for example, image scanner, fax machine, bar-code reader are all scanning devices), and voice-input devices.

Output Hardware: Output devices convert machine-readable information into people-readable form. Common output devices are monitors, printers, plotters, and voice output.

Monitors: Monitors are also called display screen or video display terminals. Most monitors that sit on desks are built in the same way as television sets, these are called cathode-ray tubes. Another type of monitor is flat-panel display, including liquid-crystal display (LCD), electroluminescent (EL) display and gas-plasma display. An LCD does not emit light of its own. Rather, it consists of crystal molecules. An electric field causes the molecules to line up in a way that alters their optical properties. Unfortunately, many LCDs are difficult to read in sunlight or other strong light. A gas-plasma display is the best type of flat screen. Like a neon light bulb, the plasma display uses a gas that emits light in the presence of an electric current.

Printer: There are four popular kinds of printers: dot-matrix, laser, ink-jet, and thermal.

Dot-Matrix Printer :Dot-matrix printers can produce a page of text in less than 10 seconds and are highly reliable. They form characters or images using a series of small pins on a print head. The pins strike an inked ribbon and create an image on paper. Printers are available with print heads of 9, 18, or 24 pins. One disadvantage of this type of printer is noise.

Laser Printer: The laser printer creates dot like images on a drum, using a laser beam light source. The characters are treated with a magnetically charged ink like toner and then are transferred from drum to paper. A heat process is used to make the characters adhere. The laser printer produces images with excellent letter and graphics quality. Ink-Jet Printer An ink-jet printer sprays small droplets of ink at high speed onto the surface of the paper. This process not only produces a letter-quality image but also permits printing to be done in a variety of colors.

Thermal Printer: A thermal printer uses heat elements to produce images on heat-sensitive paper. Color thermal printers are not as popular because of

their cost and the requirement of specifically treated paper. They are a more special use printer that produces near photographic output. They are widely used in professional art and design work where very high quality color is essential.

Plotters: Plotters are special-purpose output devices for producing bar charts, maps, architectural drawings, and even3D diagram. Plotters can produce high-quality multicolor documents and also documents that are larger in size than most printers can handle. There are four types of plotters: pen, ink-jet, electrostatic, and direct imaging.

Voice-Output Device s: Voice-output devices make sounds that resemble human speech but actually are pre-recorded vocalized sounds. Voice output is used as a reinforcement tool for learning, such as to help students study a foreign language. It is used in many supermarkets at the checkout counter to confirm purchases. Of course, one of the most powerful capabilities is to assist the physically challenged.