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Copyright 2011 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Chapter Four The Components of the System Unit Obj ti Objectives After completing this chapter, you will be able to: 1 Differentiate among various styles of system units on desktop 5 Describe the purpose and types of expansion slots and computers, notebook computers, and mobile devices adapter cards 2 Describe the control unit and arithmetic logic unit components 6 Differentiate between a port and a connector, and explain of a processor, and explain the four steps in a machine cycle the differences among a USB port and other ports 3 Define a bit and describe how a series of bits represents data 7 Describe the types of buses in a computer 4 Differentiate among the various types of memory: RAM, cache, 8 Understand how to clean a system unit on a computer or ROM, flash memory, and CMOS mobile device 156 Chapter 4 The Components of the System Unit The System Unit Whether you are a home user or a business user, you most likely will purchase a new computer or upgrade an existing computer at some time in the future. Thus, you should understand the purpose of each component in a computer. As Chapter 1 discussed, a computer includes devices used for input, pro- cessing, output, storage, and communications. Many of these components are part of the system unit. The system unit is a case that contains electronic components of the computer used to process data. System units are available in a variety of shapes and sizes. The case of the system unit is made of metal or plastic and protects the internal electronic components from damage. All computers and mobile devices have a system unit (Figure 4-1). On desktop personal computers, the electronic components and most storage devices are part of the system unit. Other devices, such as the keyboard, mouse, microphone, monitor, printer, USB flash drive, scanner, Web cam, and speakers, normally occupy space outside the system unit. An all-in-one desktop personal computer is an exception, which houses the monitor and the system unit in the same case. On most notebook computers, including netbooks, the keyboard and pointing device often occupy the area on the top of the system unit, and the display attaches to the system unit by hinges. The location of the system unit on a Tablet PC varies, depending on the design of the Tablet PC. With the slate Tablet PC (shown in Figure 4-23 on page 173), which typically does not include a keyboard, the system unit is behind the display. On a convertible Tablet PC (shown in lower-left corner of Figure 4-1), by contrast, system unit system unit system unit system unit system unit system unit system unit system unit system unit system unit system unit Figure 4-1 All sizes of computers and mobile devices have a system unit.  The Components of the System Unit Chapter 4 157 the system unit is positioned below a keyboard, and the display attaches to the system unit with a swivel- type hinge, which enables a user to rotate the display and fold it down over the keyboard to look like a slate Tablet PC. The system unit on an Ultra-Mobile PC, a smart phone, and a PDA usually consumes the entire device. On these mobile computers and devices, the display often is built into the system unit. With game consoles, the input and output devices, such as controllers and a television, reside outside the system unit. On handheld game consoles, portable media players, and digital cameras, by contrast, the packaging around the system unit houses the input devices and display. At some point, you might have to open the system unit on a desktop personal computer to replace or install a new electronic component. For this reason, you should be familiar with the electronic components of a system unit. Figure 4-2 identifies some of these components, which include the processor, memory, adapter cards, drive bays, and the power supply. The processor interprets and carries out the basic instructions that operate a computer. Memory typically holds data waiting to be processed and instructions waiting to be executed. The elec- tronic components and circuitry of the system unit, such as the processor and memory, usually are part of or are connected to a circuit board called the motherboard. Many motherboards also integrate sound, video, and networking capabilities. Adapter cards are circuit boards that provide connections and functions not built into the mother- board or expand on the capability of features integrated into the motherboard. For example, a sound card and a video card are two types of adapter cards found in some desktop personal computers today. Devices outside the system unit often attach to ports on the system unit by a connector on a cable. These devices may include a keyboard, mouse, microphone, monitor, printer, scanner, USB flash drive, card reader/writer, Web cam, and speakers. A drive bay holds one or more disk drives. The power supply allows electricity to travel through a power cord from a wall outlet into a computer. drive bay power supply sound card video card memory processor Figure 4-2 The system unit on a typical personal computer consists of numerous electronic components, some of which are shown in this figure. The sound card and video card are two types of adapter cards. 158 Chapter 4 The Components of the System Unit The Motherboard The motherboard, sometimes called a system board, is the main circuit board of the system unit. Many electronic components attach to the motherboard; others are built into it. Figure 4-3 shows a photo of a current desktop personal computer motherboard and identifies its slots for adapter cards, the processor chip, and memory. Memory chips are installed on memory cards (modules) that fit in a slot on the motherboard. A computer chip is a small piece of semiconducting material, usually silicon, on which integrated circuits are etched. An integrated circuit contains many microscopic pathways capable of carrying electrical current. Each integrated circuit can contain millions of elements such as resistors, capacitors, and transistors. Specific types of processor, memory, and other chips are discussed later in the chapter. Read Innovative Computing 4-1 to find out about chips implanted in animals. INNOVATIVE COMPUTING 4-1 Chip Implants Identify Animals When Fido and Fluffy run away, their safe return home may be Shelters and animal control centers routinely scan runaway based on data stored on a chip that veterinarians have implanted pets for chips in an attempt to reunite animals with their owners, un the skin, usually at the neck or under and some animal hospitals scan pets to determine whether they sh shoulder blades. Other animals can be have been reported lost or stolen. Most shelters require pets to ch chipped, including horses, birds, and have the implant before the animals are adopted. In addition, liv livestock. breeders, farmers, and animal associations implant the chips to Each chip is numbered uniquely and reg- thwart thieves. Researchers also use this technology to track ist istered to the owner’s name and address. migration of wild animals and fish. Th chip, sometimes called a microchip This be because it is the size of a grain of rice, con- For more information, visit the Computer Concepts ta an antenna and transponder encased tains CourseMate Web site at www.cengagebrain.com, navigate to iin a glass l tube. b The Th antenna receives low-frequency radio waves the Chapter 4 Innovative Computing resource for this book, when a scanning device passes over the chip, and the transponder and then click ID Chips. sends a signal with the chip’s number back to the scanner. slots for memory modules slot for processor chip expansion slots for adapter cards motherboard Figure 4-3 Many electronic components attach to the motherboard in a desktop personal computer, including a processor chip, memory modules, and adapter cards.  The Components of the System Unit Chapter 4 159 Processor The processor, also called the central processing unit (CPU), interprets and carries out the basic instructions that operate a computer. The processor significantly impacts overall computing power and manages most of a computer’s operations. On a personal computer, all functions of the processor usually are on a single chip. Some computer and chip manufacturers use the term microprocessor to refer to a personal computer processor chip. Most processor chip manufacturers now offer multi-core processors. A processor core contains the circuitry necessary to execute instructions. The operating system views each processor core as a separate processor. A multi-core processor is a chip with two or more separate processor cores. Two common multi-core processors are dual-core and quad-core. A dual-core processor is a chip that contains two separate processor cores. Similarly, a quad-core processor is a chip with four separate processor cores. Each processor core on a multi-core processor generally runs at a slower clock speed than a Multi-Core Processors single-core processor, but multi-core processors typically increase overall performance. For example, For more information, visit although a dual-core processor does not double the processing speed of a single-core processor, it can the Computer Concepts approach those speeds. Multi-core processors also are more energy efficient than separate multiple CourseMate Web site at www.cengagebrain.com, processors, requiring lower levels of power consumption and emitting less heat in the system unit. navigate to the Chapter 4 Processors contain a control unit and an arithmetic logic unit (ALU). These two components Web Link resource for this work together to perform processing operations. Figure 4-4 illustrates how other devices that are book, and then click connected to the computer communicate with the processor to carry out a task. Multi-Core Processors. PROCESSOR CONTROL ARITHMETIC UNIT LOGIC UNIT (ALU) instructions data information Figure 4-4 Most devices connected INPUT OUTPUT to the computer communicate with the data MEMORY information processor to carry out a task. When a DEVICES DEVICES user starts a program, for example, its instructions transfer from a storage device instructions to memory. Data needed by programs data enters memory from either an input information device or a storage device. The control unit interprets and executes instructions in memory, and the ALU performs STORAGE calculations on the data in memory. DEVICES Resulting information is stored in memory, from which it can be sent to an output device or a storage device for future access, as needed. The Control Unit The control unit is the component of the processor that directs and coordinates most of the operations in the computer. The control unit has a role much like a traffic cop: it interprets each instruction issued by a program and then initiates the appropriate action to carry out the instruc- tion. Types of internal components that the control unit directs include the arithmetic/logic unit and buses, each discussed in this chapter. 160 Chapter 4 The Components of the System Unit The Arithmetic Logic Unit The arithmetic logic unit (ALU), another component of the processor, performs arithmetic, comparison, and other operations. Arithmetic operations include basic calculations such as addition, subtraction, multiplication, and division. Comparison operations involve comparing one data item with another to determine whether the first item is greater than, equal to, or less than the other item. Depending on the result of the comparison, different actions may occur. Machine Cycle For every instruction, a processor repeats a set of four basic operations, which comprise a machine cycle (Figure 4-5): (1) fetching, (2) decoding, (3) executing, and, if necessary, (4) storing. Fetching is the process of obtaining a program instruction or data item from memory. The term decoding refers to the process of translating the instruction into signals the computer can execute. Executing is the process of carrying out the commands. Storing, in this context, means writing the result to memory (not to a storage medium). The Steps in a Machine Cycle A student enters a math Step 1 problem into the The control unit fetches memory of the computer. the math problem’s instructions and data from memory. 10 0x 0 0 48 48 The results l iin memory appear on the screen of the monitor. 4 Step 4 MEMORY Step 2 The results of the math The control unit decodes the 1 problem are stored in 3 math problem’s instructions memory. and sends the instructions PROCESSOR and data to the ALU. 2 10 0x CONTROL 48 ALU Step 3 UNIT = 480 The ALU performs 0 calculations on the data. x 48 100 Figure 4-5 This figure shows the steps in a machine cycle. The System Clock The processor relies on a small quartz crystal circuit called the system clock to control the timing of all computer operations. Just as your heart beats at a regular rate to keep your body func- tioning, the system clock generates regular electronic pulses, or ticks, that set the operating pace of components of the system unit.  The Components of the System Unit Chapter 4 161 The pace of the system clock, called the clock speed, is measured by the number of ticks per second. Current personal computer processors have clock speeds in the gigahertz range. Giga is a prefix that stands for billion, and a hertz is one cycle per second. Thus, one gigahertz (GHz) equals one billion ticks of the system clock per second. A computer that operates at 3 GHz has 3 billion (giga) clock cycles in one second (hertz). The faster the clock speed, the more instructions the processor can execute per second. The speed of the system clock is just one factor that influ- ences a computer’s performance. Other factors, such as the type of processor chip, amount of cache, memory access time, bus width, and bus clock speed, are discussed later in this chapter. Comparison of Personal Computer Processors The leading manufacturers of personal computer processor chips are Intel and AMD. These manufacturers often identify their processor chips by a model name or model number. High-performance desktop personal computers today use a processor in the Intel Core family. Less expensive, basic personal computers today use a brand of Intel processor in the Pentium or Celeron family. The Xeon and Itanium families of processors are ideal for workstations and low-end servers. AMD is the leading manufacturer of Intel-compatible processors, which have an internal design similar to Intel processors, perform the same functions, and can be as powerful, but often are less expensive. In the past, chip manufacturers listed a processor’s clock speed in marketing literature and advertise- ments. As previously mentioned, though, clock speed is only one factor that impacts processing speed in today’s computers. To help consumers evaluate various processors, manufacturers such as Intel and AMD now use a numbering scheme that more accurately reflects the processing speed of their chips. If you are ready to buy a new computer, the processor you select should depend on how you plan to use the computer. For detailed personal computer and mobile device purchasing guidelines, read the Buyer’s Guide feature that follows Chapter 7. FAQ 4-1 Which PC vendors are the most popular with Worldwide PC Market Share consumers? HP Hewlett-Packard (HP) has the highest market share worldwide 20% Dell at approximately 20 percent, with Dell in second place with 42% 13% Acer nearly 13 percent market share. HP accounts for nearly 21 6% 7% 12% Lenovo percent of PC sales in the United States. The chart to the right compares the worldwide market share for various PC vendors. Toshiba Others For more information, visit the Computer Concepts Source: Gartner CourseMate Web site at www.cengagebrain.com, navigate to the Chapter 4 FAQ resource for this book, and then click PC Vendor Market. QUIZ YOURSELF 4-1 Instructions: Find the true statement below. Then, rewrite the remaining false statements so that they are true. 1. A computer chip is a small piece of semiconducting material, usually silicon, on which integrated circuits are etched. 2. Four basic operations in a machine cycle are: (1) comparing, (2) decoding, (3) executing, and, if necessary, (4) pipelining. 3. Processors contain a motherboard and an arithmetic logic unit (ALU). 4. The central processing unit, sometimes called a system board, is the main circuit board of the system unit. 5. The leading processor chip manufacturers for personal computers are Microsoft and AMD. 6. The system unit is a case that contains mechanical components of the computer used to process data. Quiz Yourself Online: To further check your knowledge of pages 156 through 161, visit the Computer Concepts CourseMate Web site at www.cengagebrain.com, navigate to the Chapter 4 Quiz Yourself resource for this book, and then click Objectives 1 – 2. 162 Chapter 4 The Components of the System Unit Data Representation To understand how a computer processes data, you should know how a computer represents data. Most computers are digital. They recognize only two discrete states: on and off. The two digits, 0 and 1, easily can rep- BINARY DIGIT ELECTRONIC ELECTRONIC (BIT) CHARGE STATE resent these two states (Figure 4-6). The digit 0 represents the electronic state of off (absence of an electronic charge). The digit 1 represents the electronic state of on (presence of an electronic charge). ON The computer uses a binary system because it recognizes only two states. The binary system is a number system that has just two unique digits, 0 and 1, called bits. A bit (short for binary digit) is the smallest unit of data the computer can process. By itself, a bit is not very informative. OFF When 8 bits are grouped together as a unit, they form a byte. A byte provides enough different combinations of 0s and 1s to represent 256 individual characters. These characters include numbers, uppercase and Figure 4-6 A computer circuit represents the 0 lowercase letters of the alphabet, punctuation marks, and others, such as or the 1 electronically by the presence or absence the letters of the Greek alphabet. of an electronic charge. The combinations of 0s and 1s that represent characters are defined by patterns called a coding scheme. In one coding scheme, the number 8-BIT BYTE FOR THE NUMBER 4 4 is represented as 00110100, the number 0 0 1 1 0 1 0 0 6 as 00110110, and the capital letter E as 01000101 (Figure 4-7). ASCII (pronounced ASK-ee), which stands for American 8-BIT BYTE FOR THE NUMBER 6 Standard Code for Information Interchange, 0 0 1 1 0 1 1 0 is the most widely used coding scheme to represent data (Figure 4-8). Coding schemes make it possible for 8-BIT BYTE FOR THE LETTER E humans to interact with a digital computer 0 1 0 0 0 1 0 1 that processes only bits. When you press a key on a keyboard, a chip in the keyboard converts the key’s electronic signal into a Figure 4-7 Eight bits grouped together as a unit are called a byte. A byte represents a single character in the ASCII SYMBOL ASCII SYMBOL computer. 00110000 0 01001110 N 00110001 1 01001111 O 00110010 2 01010000 P 00110011 3 01010001 Q 00110100 4 01010010 R 00110101 5 01010011 S 00110110 6 01010100 T 00110111 7 01010101 U 00111000 8 01010110 V 00111001 9 01010111 W 01000001 A 01011000 X 01000010 B 01011001 Y 01000011 C 01011010 Z 01000100 D 00100001 ! 01000101 E 00100010 " 01000110 F 00100011 # 01000111 G 00100100 $ 01001000 H 00100101 % 01001001 I 00100110 & 01001010 J 00101000 ( 01001011 K 00101001 ) Figure 4-8 ASCII is a widely used 01001100 L 00101010 * coding scheme. 01001101 M 00101011 +  The Components of the System Unit Chapter 4 163 scan code that is sent to the system unit. Then, the system unit converts the scan code into a binary form the computer can process and is stored in memory. Every character is converted to its cor- responding byte. The computer then processes the data as bytes, which actually is a series of on/off electrical states. When processing is finished, software converts the byte into a human-recognizable number, letter of the alphabet, or special character that is displayed on a screen or is printed (Figure 4-9). All of these conversions take place so quickly that you do not realize they are occurring. Standards, such as those defined by ASCII, also make it possible for components in computers to communicate successfully with each other. How a Letter Is Converted to Binary Form and Back Step 1 Step 2 A user presses the capital letter The scan code for the capital letter T (SHIFT+T keys) on the keyboard, T is sent to the system unit. which in turn creates a special code, called a scan code, for the capital letter T. Step 4 Step 3 After processing, the binary The system unit converts the scan code for the capital letter T code for the capital letter T to its is converted to an image and ASCII binary code ((01010100) and displayed on the output device. stores it in memory for processing. T Figure 4-9 This figure shows how a letter is converted to binary form and back. Memory Memory consists of electronic components that store instructions waiting to be executed by the processor, data needed by those instructions, and the results of processing the data (information). Memory usually consists of one or more chips on the motherboard or some other circuit board in the computer. Memory stores three basic categories of items: (1) the operating system and other system software that control or maintain the computer and its devices; (2) application programs that carry out a specific task such as word processing; and (3) the data being processed by the application programs and resulting infor- mation. This role of memory to store both data and programs is known as the stored program concept. 164 Chapter 4 The Components of the System Unit Bytes and Addressable Memory A byte (character) is the basic storage unit in memory. When application program instructions and data are transferred to memory from storage devices, the instructions and data exist as bytes. Each byte resides tempo- seat G35 rarily in a location in memory that has an address. An address simply is seat G36 a unique number that identifies the location of the byte in memory. The illustration in Figure 4-10 shows how seats in an opera house are similar to addresses in memory: (1) a seat, which is identified by a unique seat number, holds one person at a time, and a location in memory, which is identified by a unique address, holds a single byte; and (2) both a seat, identified by a seat number, and a byte, identified by an address, can be empty. To access data or instructions in memory, the computer references the addresses that contain bytes of data. Figure 4-10 Seats in an opera Memory Sizes house are similar to Manufacturers state the size of memory (Figure 4-11) and storage devices in terms of the number addresses in memory: of bytes the chip or device has available for storage. Recall that storage devices hold data, instructions, a seat holds one and information for future use, while most memory holds these items temporarily. A kilobyte (KB or person at a time, and K) is equal to exactly 1,024 bytes. To simplify memory and storage definitions, computer users often a location in memory holds a single byte; and round a kilobyte down to 1,000 bytes. For example, if a memory chip can store 100 KB, it can hold both a seat and a byte approximately 100,000 bytes (characters). A megabyte (MB) is equal to approximately 1 million bytes. can be empty. A gigabyte (GB) equals approximately 1 billion bytes. A terabyte (TB) is equal to approximately 1 trillion bytes. Memory Sizes Approximate Approximate Number of Exact Number Number of Term Abbreviation Bytes of Bytes Pages of Text Kilobyte KB or K 1 thousand 1,024 1/2 Megabyte MB 1 million 1,048,576 500 Gigabyte GB 1 billion 1,073,741,824 500,000 Terabyte TB 1 trillion 1,099,511,627,776 500,000,000 Figure 4-11 Terms commonly used to define memory sizes. Types of Memory The system unit contains two types of memory: volatile and nonvolatile. When the computer’s power is turned off, volatile memory loses its contents. Nonvolatile memory, by contrast, does not lose its contents when power is removed from the computer. Thus, volatile memory is tem- porary and nonvolatile memory is permanent. RAM is the most common type of volatile memory. Examples of nonvolatile memory include ROM, flash memory, and CMOS. The following sections discuss these types of memory. RAM Users typically are referring to RAM when discussing computer memory. RAM (random access memory), also called main memory, consists of memory chips that can be read from and written to by the processor and other devices. When you turn on power to a computer, certain operating system files (such as the files that determine how the desktop appears) load into RAM from a storage device such as a hard disk. These files remain in RAM as long as the computer has continuous power. As additional programs and data are requested, they also load into RAM from storage.  The Components of the System Unit Chapter 4 165 The processor interprets and executes a program’s instructions while the program is in RAM. During this time, the contents of RAM may change (Figure 4-12). RAM can hold multiple programs simultaneously, provided the computer has enough RAM to accommodate all the programs. Most RAM is volatile, which means it loses its contents when the power is removed from the com- puter. For this reason, you must save any items you may need in the future. Saving is the process of copying items from RAM to a storage device such as a hard disk. How Program Instructions Transfer in and out of RAM RAM hard disk Step 1 operating system When you start the computer, certain interface operating system files are loaded into operating system RAM from the hard disk. The operating instructions system displays the user interface on the screen. RAM hard disk Step 2 Web browser window When you start a Web browser, the program’s instructions are loaded into Web browser RAM from the hard disk. The Web instructions browser and certain operating system instructions are in RAM. The Web browser window appears on the screen. RAM Web browser hard disk and paint program Step 3 windows When you start a paint program, the program’s instructions are loaded paint program into RAM from the hard disk. The paint instructions program, along with the Web browser and certain operating system instructions, are in RAM. The paint program window appears on the screen. Step 4 RAM When you quit a program, such as the Web browser, its program instructions are removed from RAM. The Web browser no longer is displayed on the screen. Web Web browser browser program window no instructions longer is are removed displayed from RAM on desktop Figure 4-12 This figure shows how program instructions transfer in and out of RAM. 166 Chapter 4 The Components of the System Unit Three basic types of RAM chips exist: dynamic RAM, static RAM, and magnetoresistive RAM. Dynamic RAM (DRAM pronounced DEE-ram) chips must be re-energized constantly or they lose their contents. Many variations of DRAM chips exist, dual inline most of which are faster than the basic DRAM. memory module memory chip Static RAM (SRAM pronounced ESS-ram) chips are faster and more reliable than any variation of DRAM chips. These chips do not have to be re-energized as often as DRAM chips, thus, the term static. A newer type of RAM, called magnetoresistive RAM (MRAM pronounced EM-ram), stores data using magnetic charges instead of electrical charges. Manufacturers claim that MRAM has greater storage capacity, consumes less power, and has faster access RAM times than electronic RAM. For more information, visit the Computer Concepts RAM chips usually reside on a memory module, which CourseMate Web site at memory slot is a small circuit board. Memory slots on the mother- www.cengagebrain.com, navigate to the Chapter 4 board hold memory modules (Figure 4-13). To learn more Web Link resource for this about how to purchase RAM for a computer, complete the Figure 4-13 This photo shows a memory book, and then click RAM. Learn How To 1 activity on pages 184 and 185. module being inserted in a motherboard. RAM Configurations The amount of RAM necessary in a computer often depends on the types of software you plan to use. A computer executes programs that are in RAM. The more RAM a computer has, the faster the computer will respond. FAQ 4-2 Retail software typically indicates the minimum amount of RAM it Can I add more RAM to my computer? requires. If you want the software to perform optimally, usually you Check your computer documentation to see how need more than the minimum specifications for the software. much RAM you can add. RAM modules are relatively Generally, home users running the latest version of Windows and inexpensive and usually include easy-to-follow instal- using basic application software such as word processing should have lation instructions. Be sure to purchase RAM that is at least 1 GB of RAM. Most business users who work with accounting, compatible with your brand and model of computer. financial, or spreadsheet programs, and programs requiring multimedia For more information, visit the Computer Concepts capabilities should have 2 to 8 GB of RAM. Users creating professional CourseMate Web site at www.cengagebrain.com, Web sites or using graphics-intensive applications will want 8 GB or more navigate to the Chapter 4 FAQ resource for this of RAM. The amount of RAM in computers purchased today ranges from book, and then click Upgrading RAM. 1 GB to 128 GB. Read Ethics & Issues 4-1 for a related discussion. ETHICS & ISSUES 4-1 How Much Technology Should Be Provided to Students and Teachers? Around the country and around the Wi-Fi networking and a simple, intuitive math. Some believe that the best approach world, local and national governments user interface. is to maintain dedicated computer lab have begun to supply schoolchildren with Supporters of these plans maintain that rooms rather than allow computers in the inexpensive notebook computers, includ- computer literacy and electronic communi- classroom. Computers require maintenance, ing netbooks. Many school districts in the cations are vital skills in today’s world, and support, and instructional time to teach United States purchase notebook comput- students should be introduced to computers students how to use the devices. Young ers for each student and hope to recoup as early in their school years as possible. children may lack the responsibility to care some of the cost by purchasing lower-cost Others claim that when students use note- for and use the computers properly. CD-based textbooks. The United Nations book computers, instructors tend to lecture endorses a plan known as One Laptop per less, requiring students to engage in more Should schools supply computers to all Child to supply $100 notebook computers research and independent study. Many students or teachers or both? Why or why to developing countries, some of which people oppose plans to equip every student not? What is the appropriate grade level already pledged to purchase millions of with a computer because they say that the at which to require computer literacy? the devices for schoolchildren. The device, technology detracts from traditional educa- Why? Should computers be relegated to a which recharges with a hand crank, includes tional subjects, such as basic reading and dedicated lab room? Why or why not?  The Components of the System Unit Chapter 4 167 Cache Most of today’s computers improve processing times with cache (pronounced cash). Two types of cache are memory cache and disk cache. This chapter discusses memory cache. Memory cache helps speed the processes of the computer because it stores frequently used instructions and data. Most personal computers today have at least two types of memory cache: L1 cache and L2 cache. L1 cache is built directly in the processor chip. L1 cache usually has a very small capacity, ranging from 8 KB to 128 KB. L2 cache is slightly slower than L1 cache but has a much larger capacity, ranging from 64 KB to 16 MB. Current processors include advanced transfer cache, a type of L2 cache built directly on the processor chip. Processors that use advanced transfer cache perform at much faster rates than those that do not use it. ROM Personal computers today typically have from 512 KB to 12 MB of advanced transfer cache. For more information, visit the Computer Concepts CourseMate Cache speeds up processing time because it stores frequently used instructions and data. When the Web site at processor needs an instruction or data, it searches memory in this order: L1 cache, then L2 cache, then www.cengagebrain.com, RAM — with a greater delay in processing for each level of memory it must search. If the instruction or data navigate to the Chapter is not found in memory, then it must search a slower speed storage medium such as a hard disk or optical disc. 4 Web Link resource for this book, and then click ROM ROM. Read-only memory (ROM pronounced rahm) refers to memory chips storing permanent data and instructions. The data How a Portable Media Player Might on most ROM chips cannot be modified — hence, the name read- Store Music in Flash Memory only. ROM is nonvolatile, which means its contents are not lost when power is removed from the computer. Step 2 Manufacturers of ROM chips often record data, instructions, or Instruct the computer to information on the chips when they manufacture the chips. These copy the music tracks ROM chips, called firmware, contain permanently written data, to a flash memory chip instructions, or information. in the portable media Step 1 player. Flash Memory Purchase and Flash memory is a type of nonvolatile memory that can be erased download music flash tracks from a Web memory electronically and rewritten. Most computers use flash memory to chip site. With one end portable media hold their startup instructions because it allows the computer easily player of a special cable USB port to update its contents. For example, when the computer changes from connected to a USB standard time to daylight savings time, the contents of a flash memory port on the system unit, chip (and the real-time clock chip) change to reflect the new time. connect the other end to Flash memory chips also store data and programs on many mobile the USB port in the computers and devices, such as smart phones, portable media play- portable media ers, PDAs, printers, digital cameras, automotive devices, digital voice player. recorders, and pagers. Some portable media players store music on flash memory chips (Figure 4-14). Others store music on tiny hard disks or flash memory cards. Flash memory cards contain flash earbuds memory on a removable device instead of a chip. Step 3 Plug the earbuds in FAQ 4-3 the portable media player, push a button How much music can I store on a portable on the portable media media player? player, and listen to the music through Portable media players that store music on flash memory chips can the earbuds. hold up to 16,000 songs. Portable media players with tiny hard disks from the have a much greater storage capacity — from 1,000 to more than computer 80,000 songs. USB port For more information, visit the Computer Concepts CourseMate Web site at www.cengagebrain.com, navigate to the Chapter 4 Figure 4-14 This figure shows how a portable media player FAQ resource for this book, and then click Portable Media Players. might store music in flash memory. 168 Chapter 4 The Components of the System Unit CMOS Some RAM chips, flash memory chips, and other types of memory chips use complementary metal-oxide semiconductor (CMOS pronounced SEE-moss) technology because it provides high speeds and consumes little power. CMOS technology uses battery power to retain information even when the power to the computer is off. Battery-backed CMOS memory chips, for example, can keep the calendar, date, and time current even when the computer is off. The flash memory chips that store a computer’s startup information often use CMOS technology. Memory Access Times Access time is the amount of time it takes the processor to read data, instructions, and information from memory. A computer’s access time directly affects how fast the computer processes data. Accessing data in memory can be more than 200,000 times faster than access- Access Time Terminology ing data on a hard disk because Term Abbreviation Speed of the mechanical motion of the hard disk. Millisecond ms One-thousandth of a second Today’s manufacturers use a Microsecond μs One-millionth of a second variety of terminology to state Nanosecond ns One-billionth of a second access times (Figure 4-15). Picosecond ps One-trillionth of a second Some use fractions of a second, which for memory occurs in Figure 4-15 Access times are measured in fractions of a second. This table lists the terms used to define access times. nanoseconds. A nanosecond (abbreviated ns) is one billionth of a second. A nanosecond is 10 million operations = 1 blink extremely fast (Figure 4-16). Other manufacturers state access times in MHz; for example, 800 MHz RAM. While access times of memory greatly affect overall computer performance, manufacturers and retailers usually list a computer’s memory in terms of its size, not Figure 4-16 It takes about one-tenth of a second to blink your eye, which is the equivalent of 100 million nanoseconds. In the its access time. time it takes to blink your eye, a computer can perform some operations 10 million times. QUIZ YOURSELF 4-2 Instructions: Find the true statement below. Then, rewrite the remaining false statements so that they are true. 1. A computer’s memory access time directly affects how fast the computer processes data. 2. A gigabyte (GB) equals approximately 1 trillion bytes. 3. Memory cache helps speed the processes of the computer because it stores seldom used instructions and data. 4. Most computers are analog, which means they recognize only two discrete states: on and off. 5. Most RAM retains its contents when the power is removed from the computer. 6. Read-only memory (ROM) refers to memory chips storing temporary data and instructions. Quiz Yourself Online: To further check your knowledge of pages 162 through 168, visit the Computer Concepts CourseMate Web site at www.cengagebrain.com, navigate to the Chapter 4 Quiz Yourself resource for this book, and then click Objectives 3 – 4.  The Components of the System Unit Chapter 4 169 Expansion Slots and Adapter Cards An expansion slot is a socket on the motherboard that can hold an adapter card. An adapter card, sometimes called an expansion card, is a circuit board that enhances functions of a component of the system unit and/or provides connections to peripherals. A peripheral is a device that connects to the system unit and is controlled by the processor in the computer. Examples of peripherals are modems, disk drives, printers, scanners, and keyboards. Figure 4-17 lists a variety of types of adapter cards. Sometimes, all functionality is built into the adapter card. With others, a cable connects the adapter card to a device, such as a digital video cam- era, outside the system unit. Some are a card that you insert in a slot on the computer. Figure 4-18 Video Cards shows an adapter card being inserted in an expansion slot on a personal computer motherboard. For more information, visit Some motherboards include all necessary capabilities and do not require adapter cards. Other the Computer Concepts motherboards may require adapter cards to provide capabilities such as sound and video. A sound CourseMate Web site at www.cengagebrain.com, card enhances the sound-generating capabilities of a personal computer by allowing sound to be navigate to the Chapter 4 input through a microphone and output through external speakers or headphones. A video card, Web Link resource for this also called a graphics card, converts computer output into a video signal that travels through a book, and then click Video cable to the monitor, which displays an image on the screen. Cards. Types of Adapter Cards Adapter Card Purpose CableCARD Allows viewing of digital cable television channels Disk controller Connects disk drives FireWire Connects to FireWire devices HDTV tuner Allows viewing of HDTV broadcasts on the monitor MIDI Connects musical instruments Modem Connects other computers through telephone lines, cable television lines, or other transmission media Network Connects other computers and peripherals PC-to-TV converter Connects a television Figure 4-18 An adapter card being inserted in Sound Connects speakers or a microphone an expansion slot on the motherboard of a personal TV tuner Allows viewing of television channels on the monitor computer. USB Connects to USB devices Video Connects a monitor Video capture Connects an analog video camera or VCR Figure 4-17 Currently used adapter cards and their functions. Removable Flash Memory Figure 4-19a (memory card) Removable flash memory includes these devices: memory cards, USB flash drives, and PC Cards/ExpressCard modules. A memory card is a removable flash memory device, usually no bigger than 1.5" in height or width, that you insert and remove from a slot in a personal computer, game console, mobile device (Figure 4-19a), or card reader/writer. Many mobile and consumer devices, such as memory card in camera slot smart phones, digital cameras, and portable media players use memory cards. Some printers and computers have built-in card Figure 4-19 Examples of removable flash readers/writers or slots that read flash memory memory in use. (continues on next page)  170 Chapter 4 The Components of the System Unit Figure 4-19b (USB flash drive) cards. In addition, you can purchase an external card reader/ writer that attaches to any computer. A USB flash drive is a flash memory storage device that plugs in USB flash drive a USB port on a computer or mobile device (Figure 4-19b). in USB port (A later section discusses USB ports.) Many desktop computers, traditional notebook computers, and Tablet PCs, have a PC Card slot or an ExpressCard slot, which is a special type of expansion slot that holds a PC Card or an ExpressCard module, respectively. Most netbooks do not have a PC Card slot or ExpressCard slot. A PC Card is a thin, credit card-sized removable flash memory device that primarily is used Figure 4-19c (ExpressCard module) today to enable traditional notebook computers and Tablet PCs to access the Internet wirelessly. An ExpressCard module, which can be used as a removable flash memory device, is about one- half the size of a PC Card and adds memory, communications, multimedia, and security capabilities to computers (Figure 4-19c). ExpressCard module in an ExpressCard slot Ports and Connectors A port is the point at which a peripheral attaches to or communicates with a system unit so that the peripheral can send data to or receive information from the computer. An external device, such as a key- board, monitor, printer, mouse, and microphone, often attaches by a cable to a port on the system unit. Instead of port, the term jack some- Figure 4-19 Examples of removable times is used to identify audio and video ports. The front and back of flash memory in use. (continued) the system unit on a desktop personal computer contain many ports (Figure 4-20). On notebook computers, including netbooks and Tablet PCs, the ports are on the back, front, and/or sides (Figure 4-21). keyboard port mouse port digital audio (or S/PDIF) digital audio in port (or S/PDIF) out port network port built-in rear surround memory serial port sound port card readers FireWire port center surround USB ports sound/subwoofer port FireWire port audio in port side surround sound port S-video port microphone microphone port port speaker port headphones port (or jack) HDMI port DVI port Figure 4-20 A system unit on a desktop personal computer has many ports on its front and back.  The Components of the System Unit Chapter 4 171 USB port network port modem port ExpressCard module slot USB ports memory card slot HDMI port serial port audio in (microphone) port audio out (headphone) port Figure 4-21 Ports on a typical notebook computer. A connector joins a cable to a port. A connector at one end of a cable attaches to a port on the system unit, and a connector at the other end of the cable attaches to a port on the peripheral. The next section discusses the more widely used ports. USB Ports A USB port, short for universal serial bus port, can connect up to 127 different peripherals together with a single connector. Devices that connect to a USB port include the following: mouse, printer, digital camera, scanner, speakers, portable media player, optical disc drive, smart phone, PDA, game console, and removable hard disk. Personal computers typically have six to eight USB ports on the front and/or back of the system unit (Figure 4-20). USB ports on mobile devices usually are smaller than those on personal computers. Figure 4-22 shows a variety of USB ports and connectors. USB Connectors and Ports Connector Port Where Used Type A Desktop computers, traditional notebook computers, netbooks, and Tablet PCs Type B Peripherals (printers, scanners, external hard disks, etc.) USB Ports For more information, visit the Computer Concepts Mini-B Mobile devices (cameras, phones, handheld game CourseMate Web site at consoles) www.cengagebrain.com, navigate to the Chapter 4 Web Link resource for this book, and then click USB Figure 4-22 A variety of USB ports and connectors are available. Ports. 172 Chapter 4 The Components of the System Unit USB 2.0, or Hi-Speed USB, is a more advanced and faster USB, with speeds 40 times higher than that of its predecessor. USB 3.0 is even faster than USB 2.0. Both USB 2.0 and USB 3.0 are backward compatible, which means they support older USB devices as well as newer USB devices. Keep in mind, though, that older USB devices do not run any faster in a newer USB port. To attach multiple peripherals using a single port, you can use a USB hub. A USB hub is a device that plugs in a USB port on the system unit and contains multiple USB ports in which you plug cables from USB devices. Some newer peripherals may attach only to a USB port. Others attach to either a serial or parallel port, as well as a USB port. FireWire Ports Previously called an IEEE 1394 port, a FireWire port is similar to a USB port in that it can FireWire connect multiple types of devices that require faster data transmission speeds, such as digital For more information, visit video cameras, digital VCRs, color printers, scanners, digital cameras, and DVD drives, to a single the Computer Concepts connector. A FireWire port allows you to connect up to 63 devices together. The three latest CourseMate Web site at versions, FireWire 800, FireWire 1600, and FireWire 3200, have speeds faster than the original www.cengagebrain.com, FireWire 400. navigate to the Chapter 4 Web Link resource for You can use a FireWire hub to attach multiple devices to a single FireWire port. A FireWire this book, and then click hub is a device that plugs in a FireWire port on the system unit and contains multiple FireWire FireWire. ports in which you plug cables from FireWire devices. Other Ports Some ports not included in typical computers but sometimes used are Bluetooth, SCSI, eSATA, IrDA, and MIDI. For a computer to have these ports, you often must customize the computer purchase order. Bluetooth Port Bluetooth technology uses radio waves to transmit data between two devices. Bluetooth devices have to be within about 33 feet of each other. Many computers, peripherals, smart phones, PDAs, cars, and other consumer electronics are Bluetooth-enabled, which means they contain a small chip that allows them to communicate with other Bluetooth-enabled comput- ers and devices. If you have a computer that is not Bluetooth enabled, you can purchase a Bluetooth wireless port adapter that will convert an existing USB port into a Bluetooth port. Also available are Bluetooth PC Cards and ExpressCard modules for traditional notebook computers and Tablet PCs, and Bluetooth cards for smart phones and PDAs. SCSI Port A special high-speed parallel port, called a SCSI port, allows you to attach SCSI (pronounced skuzzy) peripherals such as disk drives and printers. SAS (serial-attached SCSI) is a newer type of SCSI that transmits at much faster speeds than parallel SCSI. Some computers include a SCSI port. Others have a slot that supports a SCSI card. eSATA Port An eSATA port, or external SATA port, allows you to connect a high-speed external SATA (Serial Advanced Technology Attachment) hard disk to a computer. IrDA Port Some devices can transmit data via infrared light waves. For these wireless devices to transmit signals to a computer, both the computer and the device must have an IrDA port. To ensure nothing obstructs the path of the infrared light wave, you must align the IrDA port on the device with the IrDA port on the computer, similarly to the way you operate a television remote control. Devices that use IrDA ports include a smart phone, PDA, keyboard, mouse, and printer. MIDI Port A special type of port that connects the system unit to a musical instrument, such as an electronic keyboard, is called a MIDI port. Short for Musical Instrument Digital Interface, MIDI (pronounced MID-dee) is the electronic music industry’s standard that defines how devices, such as sound cards and synthesizers, represent sounds electronically. A synthesizer, which can be  The Components of the System Unit Chapter 4 173 a peripheral or a chip, creates sound from digital instructions. A system unit with a MIDI port has the capability of recording sounds that have been created by a synthesizer and then processing the sounds (the data) to create new sounds. Port Replicators and Docking Stations Instead of connecting peripherals directly to ports on a mobile computer, some mobile users prefer the flex- ibility of port replicators and docking stations. A port replicator is an external device that provides connec- tions to peripherals through ports built into the device. The mobile user accesses peripherals by connecting the port replicator to a USB port or a special port on the Tablet mobile computer. PC A docking station is similar to a port replicator, but it has more functionality. A docking station, which is an external device that attaches to a mobile computer or device, contains a power connection and provides connections to peripherals; it usually also includes slots for memory cards, optical disc drives, and other devices (Figure 4-23). With the mobile computer or device in the docking station, users can work with a full-sized key- board, a mouse, and other desktop peripherals from their traditional notebook computer, netbook, or Tablet PC. Read Looking Ahead 4-1 for a look at the next generation docking station of notebook computers. Figure 4-23 To use a slate Tablet PC while working at a desk, insert the Tablet PC in a docking station. Devices such as a keyboard and an optical disc drive can be plugged in the docking station. LOOKING AHEAD 4-1 Bendable Notebook Computers Will Slip in Your Pocket Today’s notebook computers are light and compact, any size needed and will but they will be enormous compared to what is be viewed easily outdoors. being planned for the retail marketplace in the Users with sight impair- next 10 years. Top designers at Lenovo and Intel ments can coat their screensns are designing flexible machines weighing less than with a synthetic material one pound that are thin enough to fold and place that will create 3-D shapes in a pocket. Battery life will be nearly one week, for such tactile uses as and the 256-core processors will make current reading Braille letters and computers with quad-core processors seem like blueprints. they are running at a snail’s pace. Notebook computer users will speak into a For more information, visit the Computer microphone, touch the screen, or type on a vir- Concepts CourseMate Web site at tual keyboard that does not have actual keys www.cengagebrain.com, navigate to the but can give feedback that a letter or number Chapter 4 Looking Ahead resource for this book, has been selected. Thin screens will roll out to and then click Future Notebooks. 174 Chapter 4 The Components of the System Unit Buses As explained earlier in this chapter, a computer processes and stores data as a series of electronic bits. These bits transfer internally within the circuitry of the computer along electrical channels. Each channel, called a bus, allows the various devices both inside and attached to the system unit to communicate with each other. Just as vehicles travel on a highway to move from one destination to another, bits travel on a bus (Figure 4-24). Buses are used to transfer bits from input devices to memory, from memory to the processor, from the processor to memory, and from memory to output or storage devices. Buses consist of two parts: a data bus and an address bus. The data bus is used to transfer actual data and the address bus is used to transfer information about where the data should reside in memory. The size of a bus, called the bus width, determines the number of bits that the computer can transmit at one time. For example, a 32-bit bus can transmit 32 bits (4 bytes) at a time. On a 64-bit bus, bits transmit from one location to another 64 bits (8 bytes) at a time. The larger the number of bits handled by the bus, the faster the computer transfers data. Most personal computers today use a 64-bit bus. Every bus also has a clock speed. Just like the processor, manufacturers state the clock speed for a bus in hertz. Recall that one megahertz (MHz) is equal to one million ticks per second. Today’s processors usually have a bus clock speed of 400, 533, 667, 800, 1066, 1333, or 1600 MHz. The higher the bus clock speed, the faster the transmission of data, which results in programs running faster. A computer has these basic types of buses: a system bus, possibly a backside bus, and an expan- sion bus. A system bus, also called the front side bus (FSB), is part of the motherboard and connects the processor to main memory. When computer professionals use the term bus by itself, they usually are refer- ring to the system bus. A backside bus processor (BSB) connects the processor to cache. An expansion bus allows the proces- sor to communicate with peripherals. Some peripherals outside the system unit connect to a port on an adapter card, which is inserted in an expansion slot on the motherboard. This expan- sion slot connects to the expansion bus, which allows the processor to communi- cate with the peripheral attached to the bus adapter card. Figure 4-24 Just as vehicles travel on a highway, bits travel on a bus. Buses are used to transfer bits from input devices to memory memory, from memory to the processor, chips from the processor to memory, and from memory to output or storage devices.  The Components of the System Unit Chapter 4 175 Bays After you purchase a desktop or notebook computer, you may want to install an addi- card readers tional storage device such as a disk drive in the system unit. A bay is an opening inside the system unit in which you can install additional equipment. A bay is different optical disc drives from a slot on the motherboard, which is used for the installation of adapter cards. A drive bay is a rectangular opening that typically holds disk drives. Other bays house card readers and widely used ports such as USB, FireWire, and audio ports. An external bay allows a user to access openings in the bay from outside the sys- tem unit (Figure 4-25). Optical disc drives are examples of devices installed in external bays. An internal bay is concealed entirely within the system unit. Hard disk drives are installed in internal bays. Figure 4-25 External bays usually are ports located beside or on top of one another. FAQ 4-4 How many PCs are in use worldwide? A recent study shows that more than one billion personal computers are in use worldwide, with 58 percent of these computers in the United States, Europe, and Japan. This number, expected to double by 2014, is growing rapidly because of developing markets. For more information, visit the Computer Concepts CourseMate Web site at www.cengagebrain.com, navigate to the Chapter 4 FAQ resource for this book, and then click Personal Computer Use. Power Supply Many personal computers plug in standard wall outlets, which supply an alternating current (AC) of 115 to 120 volts. This type of power is unsuitable for use with a computer, which requires a direct current (DC) ranging from 5 to more than 15 volts. The power supply is the component of the system unit that converts the wall outlet AC power into DC power. Built into the power supply is a fan that keeps the power supply cool. Some have variable speed fans that change speed or stop running, depending on temperature in the system unit. Some external peripherals such as a cable modem, speakers, or a printer have an AC adapter, which is an external power supply. One end of the AC adapter plugs in the wall outlet and the other end attaches to the peripheral. The AC adapter converts the AC power into DC power that the peripheral requires. 176 Chapter 4 The Components of the System Unit Ethics & Issues Putting It All Together For the complete text of the Ethics & Issues boxes When you purchase a computer, it is important to understand how the components of the system found in this chapter, visit unit work. Many components of the system unit influence the speed and power of a computer. the Computer Concepts These include the type of processor, the clock speed of the processor, the amount of RAM, bus CourseMate Web site at width, and the clock speed of the bus. The configuration you require depends on your intended use. www.cengagebrain.com and then navigate to the Read Ethics & Issues 4-2 for a related discussion. Chapter 4 Ethics & Issues The table in Figure 4-26 lists the suggested minimum processor and RAM requirements based resource for this book. on the needs of various types of computer users. ETHICS & ISSUES 4-2 Suggested Minimum Configurations Is Government Search and Seizure by User of Computers Ethical? User Processor and RAM In the interest of national security, the Home Intel Core i5 or Department of Homeland Security may search Intel Core i3 or and seize any mobile computer or device from AMD Athlon II or people arriving in the United States. The some- AMD Sempron times random searches may be done without a warrant or even a reason. Additionally, the government has taken computers from schools Minimum RAM: 2 GB and libraries in a similar manner. Computers and mobile devices might be taken away for S ll Office/Home Small /H Office Intel Core i7 or an off-site inspection for any amount of time. Intel Core i7 Extreme or Sometimes, the devices are not returned and AMD Phenom II or little or no reason is given for the seizure. AMD Athlon II At airports and other points of entry to the country, the government considers computers and mobile devices to be containers, just as Minimum RAM: 4 GB a piece of luggage is a container. Computers, therefore, can be searched and seized similarly M bil Mobile Intel Core i7 Extreme or to luggage without reasonable suspicion. Intel Core i7 or Opponents claim that the data on a computer AMD Phenom II or is like memories stored in the brain. They claim AMD Turion II that the government should be able to inspect the hardware, but not the contents of memory or hard disk. Librarians and school administra- Minimum RAM: 2 GB tors claim that the government is invading the privacy of patrons and students. P Power Intel Xeon or Intel Itanium or Is government search and seizure of AMD Opteron computers without a warrant ethical? Why or why not? Would you allow a government employee to inspect the data on your mobile computer or device? Why or why not? If mem- ories, thoughts, or intentions in one’s mind Minimum RAM: 8 GB could someday be deciphered by a computer E t p i Enterprise Intel Core i7 or at a security checkpoint, should the government Intel Core i7 Extreme or be allowed to scan them? Why? AMD Phenom II or AMD Athlon II Minimum RAM: 4 GB Figure 4-26 Suggested processor and RAM configurations by user.  The Components of the System Unit Chapter 4 177 Keeping Your Computer or Mobile Device Clean Over time, the system unit collects dust — even in a clean environment. Built up dust can block airflow in a computer or mobile device, which can cause it to overheat, corrode, or even stop working. By cleaning your computer or mobile device once or twice a year, you can help extend its life. This preventive maintenance requires a few basic products (Figure 4-27): can of compressed air — removes dust and lint from difficult-to-reach areas; removes sticky liquid spilled on keyboards lint-free antistatic wipes and swabs screen cleaning solution or 50/50 mix of rubbing alcohol and water (do not use ammonia-based solutions) small computer vacuum (or small attachment