CCNA 1 and 2 Companion Guide, Revised (Cisco Networking Academy Program) part 5

1102.book Page 9 Tuesday, May 20, 2003 2:53 PM PC Basics 9 Figure 1-3 Motherboard Read-only memory (ROM)—A type of computer memory in which data has been prerecorded. After data has been written onto a ROM chip, it cannot be removed and can only be read. A version of ROM known as EEPROM (electron-ically erasable programmable read-only memory) can be written to. It is called Flash memory or firmware. The basic input/output system (BIOS) in most PCs is stored in EEPROM. Expansion slot—An opening in a computer, usually on the motherboard, where an expansion card can be inserted to add new capabilities to the computer (see Figure 1-4). System unit—The main component of the PC system. It includes the case, chassis, power supply, microprocessor, main memory, bus, expansion cards, disk drives (floppy, CD hard disk, and so on), and ports. The system unit does not include the keyboard, the monitor, or any other external devices connected to the computer. Power supply—Supplies power to a computer. 1102.book Page 10 Tuesday, May 20, 2003 2:53 PM 10 Chapter 1: Introduction to Networking Figure 1-4 Expansion Slot NOTE Some computers have a network card, sound card, video card, and other cards integrated into the motherboard. Motherboard Components The motherboard is the computer’s main circuit board. It is crucial because it is the nerve center of the computer system. Everything else in the system plugs into it, is con-trolled by it, and depends on it to communicate with other devices in the system. The following list describes the motherboard’s various components: Backplane—A large circuit board that contains sockets for expansion cards. Memory chips—RAM chips on memory cards plug into the motherboard. Network interface card (NIC)—A printed circuit board that provides network communication capabilities to and from a PC. Many newer desktop and laptop computers have an Ethernet NIC built into the motherboard. Video card—A board that plugs into a PC to give it display capabilities. Video cards typically include onboard microprocessors and additional memory to speed up and enhance graphics display. Sound card—An expansion board that handles all sound functions. Parallel port—An interface that can transfer more than 1 bit at a time. It is used to connect external devices, such as printers. Serial port—An interface used for serial communication in which only 1 bit is transmitted at a time. The serial port can connect to an external modem, plotter, or serial printer. It can also be used to connect to networking devices such as routers and switches as a console connection. Mouse port—Connects a mouse to a PC. Keyboard port—Connects a keyboard to a PC. 1102.book Page 11 Tuesday, May 20, 2003 2:53 PM PC Basics 11 Power cord—Connects an electrical device to an electrical outlet to provide power to the device. Universal Serial Bus (USB) port—This interface lets peripheral devices such as mice, modems, keyboards, scanners, and printers be plugged in and unplugged without resetting the system. USB ports eventually might replace serial and paral-lel ports. Lab Activity PC Hardware This lab helps you become familiar with the basic peripheral components of a PC system and their connections, including network attachment. You examine the internal PC configuration and identify major components. You also observe the boot process for the Windows operating system and use the Control Panel to find out information about the PC hardware. Desktop Versus Laptop Laptop and notebook computers are becoming increasingly popular. The main differ-ence between desktop PCs and laptops, other than the fact that laptop components are smaller than those found in a PC, is that laptops offer more mobility and portability than desktop PCs. The expansion slots are called Personal Computer Memory Card International Association (PCMCIA) card slots or PC card slots in laptop computers. The PC card slots are where devices such as NICs, modems, hard drives, and other useful devices (usually the size of a thick credit card) are connected. Figure 1-5 shows a PC card adapter for a wireless local-area network (WLAN). Figure 1-5 PC Card 1102.book Page 12 Tuesday, May 20, 2003 2:53 PM 12 Chapter 1: Introduction to Networking Network Interface Cards As shown in Figure 1-6, a NIC is a printed circuit board that provides network com-munication capabilities to and from a PC. Also called a LAN adapter, a NIC plugs into a motherboard and provides a port for connecting to the network. The NIC consti-tutes the computer interface with the LAN. Figure 1-6 Network Interface Card The NIC communicates with the network through a cable and with the computer via an expansion slot. When a NIC is installed in a computer, it requires an interrupt request (IRQ) for service from the CPU, as well as an input/output (I/O) address, a memory space for the operating system (such as Linux or Windows), and drivers to perform its function. An IRQ is a signal that informs a CPU that an event needing its attention has occurred. An IRQ is sent over a hardware line to the microprocessor. An example of an interrupt being issued is a key being pressed on the keyboard. The CPU must move the character from the keyboard to RAM. An I/O address is a location in memory used to enter data into or retrieve data from a computer using an auxiliary device. When selecting a NIC for a network, consider the following: Type of network—Different types of networks use different types of NICs. For example, Ethernet NICs are designed for Ethernet LANs. Some other types of networks include Token Ring and Fiber Distributed Data Interface (FDDI). Ethernet is by far the most common. Type of medium—The type of port or connector used by the NIC for network connection is specific to the medium type, such as twisted-pair, coaxial, fiber-optic, or wireless. Coaxial is becoming increasingly rare. 1102.book Page 13 Tuesday, May 20, 2003 2:53 PM PC Basics 13 Type of system bus—There are different types of system buses, such as PCI and ISA. Because PCI slots are faster than ISA slots, the latter are being phased out. NIC and Modem Installation Connectivity to the Internet requires an adapter card, which might be a modem or NIC. A modem is an electronic device that is used for computer communications through telephone lines. It allows data transfer between one computer and another over the Public Switched Telephone Network (PSTN). Figure 1-7 shows an example of an external modem. Typically, modems send data in blocks of bytes. After each block, basic math is performed to analyze the block, and the computer on the receiving end is asked whether it agrees with the results. If any differences appear, the block is sent again. The modems convert digital data to analog signals for transmission over the PSTN and then convert analog signals back to digital data on the receiving end. Figure 1-7 External Modem The term modem derives from the function of this device. The process of converting digital signals to analog and back again is called modulation/demodulation (hence the term modem). Modems can be installed internally or attached to the computer via a serial or USB interface externally. Modems connect a computer to the network by dial-ing the telephone number of another computer’s modem, typically that of the Internet service provider (ISP). The NIC lets hosts connect to the network. The NIC is considered a key component. NICs are available in different types, depending on the individual device configuration. Notebook computers can have a built-in interface or use a PCMCIA card. Desktop systems can use a built-in or adapter card-type NIC. ... - tailieumienphi.vn