CHAPTER 2 How Hardware and Software Work Together

1 How Hardware and SoftwareWork Togetheromputer systems contain both Hardware andsoftware, and computer technicians mustunderstand how they interact. Although the phys-ical Hardware is the visible part of a computersystem, the Software is the intelligence of the sys-tem that enables the Hardware components towork. After reading this CHAPTER , you shouldhave a general understanding of how hardwareand Software work Together , and what happenswhen a PC is first turned on. You will also learn about error messages that can occurduring the boot. You can look at this CHAPTER as your crash course on operatingsystems from the perspective of a Hardware technician!In this CHAPTER , you will learn: How an operating system manageshardware How system resources help hardwareand Software communicate The steps involved in booting yourcomputerC392 CHAPTERC2223_CH02_39 How an Operating System Manages HardwareAn operating system (OS) is Software that controls a computer.

2 It manages Hardware ,runs applications, provides an interface for users, and stores, retrieves, and manipu-lates files. In general, an operating system acts as the middleman between applica-tions and Hardware (see Figure 2-1).PrinterRAMHard driveCPUROM BIOSH ardwareApplication(MS-Word)Operating system (Windows XP)Figure 2-1 Users and applications depend on the OS to relate to all Hardware componentsSeveral applications might be installed on a computer to meet various user needs,but it only needs one operating system. The most popular operating systems for per-sonal computers today are Microsoft Windows XP, Windows 2000, and Windows98/Me. Other Microsoft operating systems for PCs that are outdated or becomingoutdated are Windows NT, Windows 95, and DOS.

3 There are other OSs not madeby Microsoft, including Linux and the Mac OS. When you learn about Hardware , itis sometimes important to know how an OS installs devices and how to use the OS tohelp in troubleshooting a failed device. In this book, for these purposes, we will beusing Windows XP or Windows 98, as these are the OSs you are most likely to becalled on to operating system is responsible for communicating with Hardware , but the OSdoes not relate directly to the Hardware . Rather, the OS uses device drivers or theBIOS to interface with Hardware . Figure 2-2 shows these relationships. Therefore,most PC Software falls into three categories: Device drivers or the BIOS Operating system Application software40 CHAPTER 2 How Hardware and Software Work TogetherC2223_CH02_40 Operating systemHard driveOperating systemApplicationsUserKernelDevicedriver sDevicedriversSystemBIOSV ideocardFloppy diskdriveBIOSF igure 2-2An OS relates to Hardware by way of BIOS and device driversDevice drivers are small programs stored on the hard drive that tell the computerhow to communicate with a specific Hardware device such as a printer, network card,or modem.

4 Recall from CHAPTER 1 that the basic input/output system (BIOS) on themotherboard is hard-coded or permanently coded into a computer chip called theROM BIOS chip or firmware chip. BIOS programs fall into three categories: pro-grams to control I/O devices (called system BIOS), programs to control the startup ofa computer (called startup BIOS), and a program to change the setup informationstored in CMOS (called CMOS setup). Next we look at how an OS uses devicedrivers and the BIOS to manage an OS Uses Device DriversDevice drivers are Software designed to interface with specific Hardware are stored on the hard drive and installed when the OS is first installed or whennew Hardware is added to a system.

5 The OS provides some device drivers, and themanufacturer of the specific Hardware device with which they are designed to inter-face provides others. In either case, unlike BIOS, device drivers are usually written fora particular OS and might need to be rewritten for use with you purchase a printer, DVD drive, Zip drive, digital camera, scanner, orother Hardware device, bundled with the device is a set of floppy disks or CDs thatA+ an Operating System Manages Hardware412C2223_CH02_41contain the device drivers (see Figure 2-3). You must install these device driversunder the operating system so it will have the necessary Software to control thedevice. In most cases, you install the device and then install the device drivers.

6 Thereare a few exceptions, such as a digital camera using a USB port to download this case, most often you install the Software to drive the digital camera before youplug in the camera. See the device documentation to learn what to do first. Laterchapters cover device driver 2-3A device such as this CD-ROM drive comes packaged with its device drivers stored on afloppy disk or other media. Alternately, you can use device drivers built into the drivers come from a number of sources. Some come with and are part of the operatingsystem, some come with Hardware devices when they are purchased, and some are provided fordownloading over the Internet from a device manufacturer s Web are two kinds of device drivers: 16-bit real-mode drivers and 32-bit pro-tected-mode drivers.

7 Windows 95 and Windows 98 support both, but Windows Meand Windows NT/2000/XP use only 32-bit drivers. Windows 9x and Windows2000/XP provide hundreds of 32-bit drivers for many different kinds of devices, anddevice manufacturers also provide their own 16- or 32-bit drivers, which come bun-dled with the device or can be downloaded from the device manufacturer s Web installing a new Hardware device on a Windows 2000/XP system, alwayscheck the Hardware compatibility list (HCL) to determine if a driver will work underWindows 2000/XP. 42 CHAPTER 2 How Hardware and Software Work TogetherA+ to the Microsoft Web site and search for your the device does not install properly or produces errors, check the manufacturer sWeb site for a driver that the manufacturer says is compatible with Windows2000 2000/XP and Windows 9x keep information about 32-bit drivers in theWindows registry, a database of Hardware and Software settings, Windows configura-tion settings, user parameters, and application , to address bugs, make improvements, or add features, manufacturersrelease device drivers that are more recent than those included with Windows or bun-dled with the device.

8 Whenever possible, it is best to use the latest driver available fora device provided by the device manufacturer. You can usually download theseupdated drivers from the manufacturer s Web site. You will learn how to install,update, and troubleshoot drivers in later chapters. APPLYINGCONCEPTSS uppose you have just borrowed an HP 995c Deskjet printer from a friend, but you forgot toborrow the CD with the printer drivers on it. You could go to the Hewlett-Packard Web site( ), download the drivers to a folder on your PC, and install the driver under Win-dows. Figure 2-4 shows you a Web page from the site listing downloadable drivers for inkjetprinters. Search the HP site and find the driver for your borrowed HP 995c 2-4 Download the latest device drivers from a manufacturer s Web siteHow an Operating System Manages Hardware43A+ an OS Uses System BIOS to Manage DevicesThe OS communicates with simple devices, such as floppy drives or keyboards,through system BIOS.

9 In addition, system BIOS can be used to access the hard some cases, an OS has a choice of using system BIOS or device drivers to access adevice. Most often it uses device drivers because they are faster. The trend today is touse device drivers rather than the BIOS to manage is a good way to determine whether the BIOS or a device driver is controlling a device. Ifthe device is configured using CMOS setup, most likely system BIOS controls it. If the device isconfigured using the OS, most likely a driver controls it. Sometimes you can use the WindowsSystem Information or Device Manager utilities to find out the name of a driver controlling example, in Figure 2-5, the setup main menu for an Award BIOS system letsyou configure, or set, the system date and time, the Supervisor Password (power-onpassword), floppy disk drives, the hard drive, and the keyboard.

10 Figure 2-6 showsanother setup window for this same BIOS that can configure serial ports, an infraredport, and a parallel port. System BIOS can control all these devices. On the otherhand, there is no setup window in this BIOS to control the DVD drive or Zip driveinstalled on this system. The BIOS is not aware of these devices; this means they arecontrolled by device setup windows are accessed during startup. A system displays a message at the bottom ofthe screen saying something like, Press Del to enter setup. Pressing the indicated key launchesa program stored on the ROM BIOS microchip to change the contents of CMOS RAM. This BIOS setup program provides windows like those in Figures 2-5 and that the system BIOS is stored in ROM.