cis

Head crash

A head crash occurs when a read/write head touches the surface of a platter, usually resulting in a loss of data or sometimes loss of the entire disk. Although current internal hard disks are built to withstand shocks and are sealed tightly to keep out contaminants, head crashes occasionally still do occur. Thus, it is crucial that you back up a hard disk regularly.

Heat sink

A heat sink is a small ceramic or metal component with fins on its surface that absorbs and disperses heat produced by electrical components, such as a processor. Many heat sinks have fans to help distribute air dissipated by the heat sink. Some heat sinks are packaged as part of a processor chip. Others are installed on the top or the side of the chip (Figure 6-6). Some computers use liquid cooling technology to reduce the temperature of a processor. Liquid cooling technology uses a continuous flow of fluid(s), such as water and glycol, in a process that transfers the heated fluid away from the processor to a radiator-type grill, which cools the liquid, and then returns the cooled fluid to the processor. Laptop users often use a cooling pad to help further reduce the heat generated by their computer. A cooling pad rests below a laptop and protects the computer from overheating and also the user's lap from excessive heat (Figure 6-7). Some cooling pads contain a small fan to transfer heat away from the laptop. These types of cooling pads often draw power from a USB port. Instead of using power, other pads absorb heat through a conductive material inside the pad

storage

A storage medium, also called secondary storage, is the physical material on which a computer keeps data, information, programs, and applications. Examples of storage media include hard disks, solid-state drives (both of which can be internal or external), memory cards, USB flash drives, optical discs, network attached storage devices, magnetic stripe cards, smart cards, RFID tags, and NFC tags. Another storage option is cloud storage, which keeps information on servers on the Internet. Because the user accesses files on cloud storage through a browser using an app from the storage provider, the actual media on which the files are stored are transparent to the user. Figure 8-1 shows a variety of storage options. In addition to programs and apps, users store a variety of data and information on storage media in their computers and mobile devices or on cloud storage. For example, many users store digital photos, appointments, schedules, contacts, email messages, and tax records. A home user also might store budgets, bank statements, a household inventory, stock purchase records, homework assignments, recipes, music, and videos. In addition or instead, a business user stores reports, financial records, travel records, customer orders and invoices, vendor payments, payroll records, inventory records, presentations, quotations, and contracts. Business and power users store diagrams, drawings, blueprints, designs, marketing literature, corporate newsletters, and product catalogs. A storage device is the hardware that records and/or retrieves items to and from storage media. Writing is the process of transferring data, instructions, and information from memory to a storage medium. Reading is the process of transferring these items from a storage medium into memory. When storage devices write on storage media, they are creating output. Similarly, when storage devices read from storage media, they function as a source of input. Nevertheless, they are categorized as storage devices, not as input or output devices

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 one another. Just as vehicles travel on a highway to move from one destination to another, bits travel on a bus (Figure 6-18). 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 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. Bus Width 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. Using the highway analogy again, assume that one lane on a highway can carry one bit. A 32-bit bus is like a 32-lane highway. A 64-bit bus is like a 64-lane highway. If a number in memory occupies 8 bytes, or 64 bits, the computer must transmit it in two separate steps when using a 32-bit bus: once for the first 32 bits and once for the second 32 bits. Using a 64-bit bus, the computer can transmit the number in a single step, transferring all 64 bits at once. The wider the bus, the fewer number of transfer steps required and the faster the transfer of data. Most personal computers today use a 64-bit bus. In conjunction with the bus width, many computer professionals refer to a computer's word size. Word size is the number of bits the processor can interpret and execute at a given time. That is, a 64-bit processor can manipulate 64 bits at a time. Computers with a larger word size can process more data in the same amount of time than computers with a smaller word size. In most computers, the word size is the same as the bus width.

Cloud Computing

Cloud Computing Recall that cloud computing refers to an environment of servers that house and provide access to resources users access via the Internet. Home and business users choose cloud computing for a variety of reasons: • Accessibility: Data and/or applications are available worldwide from any computer or device with an Internet connection. • Cost savings: The expense of software and high-end hardware, such as fast processors and high-capacity memory and storage devices, shifts away from the user. • Space savings: Floor space required for servers, storages devices, and other hardware shifts away from the user. • Scalability: Provides the flexibility to increase or decrease computing requirements as needed. Cloud computing consists of a front end and a back end, connected to each other through a network. The front end includes the hardware and software with which a user interacts to access the cloud. For example, a user might access a resource on the cloud through a browser on a laptop. The back end consists of the servers and storage devices that manage and store the resources accessed by users. Mini Feature 6-2: Cloud Computing Services Cloud computing allows companies to outsource, or contract to third-party providers, elements of their information technology infrastructure. They pay only for the computing power, storage, bandwidth, and access to applications that they actually use. As a result, companies need not make large investments in equipment, or the staff to support it. Read Mini Feature 6-2 to learn about available types of cloud computing services.

CD

Disc Burning Disc burning software writes text, graphics, audio, and video files on a recordable or rewritable disc. This software enables home users easily to back up contents of their hard drive on an optical disc (CD/DVD) and make duplicates of uncopyrighted music or movies. Disc burning software usually also includes photo editing, audio editing, and video editing capabilities.

Flash Memory

Flash memory is a type of nonvolatile memory that can be erased electronically and rewritten. Most computers use flash memory to hold their start-up instructions because it allows the computer to update its contents easily. For example, when the computer changes from standard time to daylight savings time, the contents of a flash memory chip (and the real-time clock chip) change to reflect the new time. Flash memory chips also store data and programs on many mobile devices and peripheral devices, such as smartphones, portable media players, printers, digital cameras, automotive devices, and digital voice recorders. When you enter names and addresses in a smartphone, for example, a flash memory chip stores the data. Some portable media players store music on flash memory chips; others store music on tiny hard drives or memory cards. Memory cards contain flash memory on a removable device instead of a chip. Read Secure IT 6-4 for tips about deleting data on a smartphone.

Machine Cycle

Machine Cycle For every instruction, a processor repeats a set of four basic operations, which comprise a machine cycle: (1) fetching, (2) decoding, (3) executing, and, if necessary, (4) storing. • Fetching is the process of obtaining a program or an application instruction or data item from memory. • 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).

Memory Cache

Memory cache helps speed the processes of the computer because it stores frequently used instructions and data. Most personal computers today have two types of memory cache: Level 1 (L1) cache and Level 2 (L2) cache. Some also have Level 3 (L3) cache. • L1 cache is built directly on the processor chip. L1 cache usually has a very small capacity. • L2 cache is slightly slower than L1 cache but has a much larger capacity. Current processors include advanced transfer cache (ATC), a type of L2 cache built directly on the processor chip. Processors that use ATC perform at much faster rates than those that do not use it. • L3 cache is a cache on the motherboard that is separate from the processor chip. L3 cache exists only on computers that use L2 advanced transfer cache. When the processor needs an instruction or data, it searches memory in this order: L1 cache, then L2 cache, then L3 cache (if it exists), then RAM — with a greater delay in processing for each level of memory it must search (Figure 6-14). If the instruction or data is not found in memory, then it must search a slower speed storage medium, such as a hard drive or optical disc. Discover More: Visit this chapter's free resources to learn more about memory cache.

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 programs that control or maintain the computer and its devices 2. Applications that carry out a specific task, such as word processing 3. The data being processed by the applications and the resulting information This role of memory to store both data and programs is known as the stored program concept.

Processor Cooling

Processor chips for laptops, desktops, and servers can generate quite a bit of heat, which could cause the chip to malfunction or fail. Although the power supply on some computers contains a main fan to generate airflow, today's personal computer processors often require additional cooling. Some computer cases locate additional fans near certain components, such as a processor, to provide additional cooling. Heat sinks, liquid cooling technologies, and cooling mats often are used to help further dissipate processor heat. A heat sink is a small ceramic or metal component with fins on its surface that absorbs and disperses heat produced by electrical components, such as a processor. Many heat sinks have fans to help distribute air dissipated by the heat sink. Some heat sinks are packaged as part of a processor chip. Others are installed on the top or the side of the chip (Figure 6-6). Some computers use liquid cooling technology to reduce the temperature of a processor. Liquid cooling technology uses a continuous flow of fluid(s), such as water and glycol, in a process that transfers the heated fluid away from the processor to a radiator-type grill, which cools the liquid, and then returns the cooled fluid to the processor. Laptop users often use a cooling pad to help further reduce the heat generated by their computer. A cooling pad rests below a laptop and protects the computer from overheating and also the user's lap from excessive heat (Figure 6-7). Some cooling pads contain a small fan to transfer heat away from the laptop. These types of cooling pads often draw power from a USB port. Instead of using power, other pads absorb heat through a conductive material inside the pad.

ROM

ROM Read-only memory (ROM pronounced rahm) refers to memory chips storing permanent data and instructions. The data on most ROM chips cannot be modified — hence, the name read-only. ROM is nonvolatile, which means its contents are not lost when power is removed from the computer. In addition to computers and mobile devices, many peripheral devices contain ROM chips. For example, ROM chips in printers contain data for fonts. Manufacturers of ROM chips often record data, instructions, or information on the chips when they manufacture the chips. These ROM chips, called firmware, contain permanently written data, instructions, or information, such as a computer or mobile device's start-up instructions. Read Ethics & Issues 6-2 to consider issues related to the manufacture of computer and mobile device components.

Registers

Registers A processor contains small, high-speed storage locations, called registers, that temporarily hold data and instructions. Registers are part of the processor, not part of memory or a permanent storage device. Processors have many different types of registers, each with a specific storage function. Register functions include storing the location from where an instruction was fetched, storing an instruction while the control unit decodes it, storing data while the ALU calculates it, and storing the results of a calculation.

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. For example, to determine if an employee should receive overtime pay, software instructs the ALU to compare the number of hours an employee worked during the week with the regular time hours allowed (e.g., 40 hours). If the hours worked exceed 40, for example, software instructs the ALU to perform calculations that compute the overtime wage.

The Control Unit

The control unit is the component of the processor that directs and coordinates most of the operations in the computer. That is, it interprets each instruction issued by a program or an application and then initiates the appropriate action to carry out the instruction. Types of internal components that the control unit directs include the arithmetic logic unit, registers, and buses, each discussed in this chapter.

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 functioning, the system clock generates regular electronic pulses, or ticks, that set the operating pace of components of the system unit. Each tick equates to a clock cycle. Processors today typically are superscalar, which means they can execute more than one instruction per clock cycle. 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 influences 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.

Processor CPU

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 larger computers, such as mainframes and supercomputers, the various functions performed by the processor extend over many separate chips and often multiple circuit boards. 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.

Hard Drives

The term, hard drive, refers collectively to hard disks and SSDs. Hard drives can be internal or external. That is, they can reside inside a computer or mobile device, or they can be an external device that connects to a computer or some mobile devices. The following sections discuss the characteristics of internal and external hard disks and SSDs. Hard Disk A hard disk, also called a hard disk drive (HDD), is a storage device that contains one or more inflexible, circular platters that use magnetic particles to store data, instructions, and information. Depending on how the magnetic particles are aligned, they represent either a 0 bit or a 1 bit. Recall from Chapter 7 that a bit (binary digit) is the smallest unit of data a computer can process. Thus, the alignment of the magnetic particles represents the data. Desktops and laptops often contain at least one hard disk. The entire hard disk is enclosed in an airtight, sealed case to protect it from contamination (Figure 8-4). Read Ethics & Issues 8-1 to consider whether governments should be able to confiscate computers and mobile devices to search the content of hard drives and other media.

USB

Usb Flash Drives As mentioned in Chapter 1, a USB flash drive, sometimes called a thumb drive, is a flash memory storage device that plugs in a USB port on a computer or mobile device (Figure 8-13). USB flash drives are convenient for mobile users because they are small and lightweight enough to be transported on a keychain or in a pocket. With a USB flash drive, users easily transfer documents, photos, music, and videos from one computer to another. Storage capacities of USB flash drives vary. Read Secure IT 8-2 for pointers about safely removing a USB flash drive and other media. Discover More: Visit this chapter's free resources to learn more about USB flash drives.

RAM

Users typically are referring to RAM when discussing computer and mobile device 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 or mobile device, certain operating system files (such as the files that determine how the desktop or home screen appears) load into RAM from a storage device such as a hard drive. These files remain in RAM as long as the computer or mobile device has continuous power. As additional applications and data are requested, they also load into RAM from storage. The processor interprets and executes a program or application's instructions while the program or application is in RAM. During this time, the contents of RAM may change (Figure 6-12). RAM can accommodate multiple programs and applications simultaneously. Most RAM is volatile, which means it loses its contents when the power is removed from the computer. For this reason, you must save any data, instructions, and information you may need in the future. Saving is the process of copying data, instructions, and information from RAM to a storage device such as a hard drive. Types of RAM Two common types of RAM are dynamic RAM and static RAM: • Dynamic RAM (DRAM pronounced DEE-ram) chips must be reenergized constantly or they lose their contents. Many variations of DRAM chips exist, most of which are faster than the basic DRAM (Table 6-1). • 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 reenergized as often as DRAM chips; hence, the term, static. SRAM chips, however, are much more expensive than DRAM chips. Special applications, such as cache, use SRAM chips. A later section in this chapter discusses cache. Read How To 6-2 for instructions about determining memory requirements