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Chapter7249ADVANCED HARDWARE CONFIGURATION FIGURE 7-4A 68-pin LPT SCSI connector68-pin LPT type connector used with 16-bit- wide data paths. Mainboard Flow Control: IRQs,DMAs,and I/O AddressesRecall from the preceding section that multiple SCSI devices attached to a single controllercard need to be uniquely identified and their requests for service prioritized.The same is trueof multiple devices attached to the mainboard via expansion slots.Recall that the unique iden- tifier used with peripheral components is the Interrupt Request (IRQ). The processor of a computer executes processes in physical memory for devices.Its time andcapacity must be shared among all devices in the computer,which can be accomplished in oneof two ways:polling or interruption.In polling,the processor polls system devices to see if thereare tasks to be run.Not all devices have processes to run and,thus,the processor wastes timeand resources polling them.There is also no efficient way of prioritizing tasks using processorpolling.The second method is a more effective way to share processor time;the processor isinterrupted by devices only when resources are needed.IRQs are so named because they areused to identify devices and give priorities that are considered when a device needs to accessthe processor.If two devices require access to the processor at the same time,the one with thelowest IRQ (highest priority) is given access first. Initially,eight IRQs were created to identify and prioritize devices attached to the original ISAslots that used an 8-bit wide data path and were numbered 0 through 7.The highest prioritywas given the lowest number,thus a device with an IRQ of 0 had a higher priority than a deviceassigned an IRQ of 4.With the evolution of the 16-bit wide ISA expansion slot came the needfor eight more IRQs,numerically identified as 8 through 15.Unlike SCSI,however,theseadditional IRQs were not appended to the priority list,but rather squeezed into the middleof the priority sequence between IRQ 2 and IRQ 3.This means that IRQs do not follow astraightforward priority order;although IRQ 10 has higher priority than IRQ 13,IRQ 10also has a higher priority than IRQ 4.The IRQ priority scheme is illustrated in Figure 7-5. FIGURE 7-5IRQ priorities

SCSI technology has evolved over time;it was initially adopted as an industry-defined stan- dard in 1986.At that time,SCSI used an 8-bit-wide data path on a controller card that heldup to seven devices and had a data transfer speed of 5MB per second.This was commonlyreferred to as SCSI-1 (SCSI Standard 1).By 1994,it had evolved to a standard that used a 16- bit-wide data path on a controller card that could hold up to 15 devices and had a transfer speedof 20MB per second.This advent was referred to as SCSI-2 (SCSI Standard 2).SCSI-3 wasintroduced a short time later and provided speeds of over 160MB per second.Newer technol- ogy,such as FireWire (IEEE 1394),can transfer data to and from SCSI devices at speeds over800MB per second.Table 7-1 describes various SCSI technologies. Table 7-1 Common SCSI standardsSpeed Bus WidthNumber ofSCSI Type(MB/s)(bits)ConnectorDevices SupportedSCSI-1 (narrow,slow)5850-pin Centronics or 750-pin LPT (Line Port Terminal) typeSCSI-2 (Fast)10850-pin LPT type7SCSI-2 (Wide)201668-pin LPT type15SCSI-3 1668-pin LPT type15(Ultra)40(Ultra2 Wide)80(Ultra3 Wide)160You can identify the type of SCSI device by observing the connector.To identify a SCSI-1 50- pin Centronic or LPT connector,you can compare them to Figures 7-2 and 7-3,respectively. SCSI-2 devices initially used a 50-pin LPT connector,as shown in Figure 7-3.However,laterversions of SCSI-2 and SCSI-3 used a 68-pin LPT connector,as depicted in Figure 7-4.248Chapter 7ADVANCED INSTALLATION FIGURE 7-2A 50-pin Centronics SCSI connector50-pin Centronic connector used with older 8-bit- wide data path devices.Normally held in place viaspring clips. FIGURE 7-3A 50-pin LPT SCSI connector50-pin LPT connector used for 8-bit-widedata paths.

Chapter7247ADVANCED HARDWARE CONFIGURATIONFIGURE 7-1Connecting SCSI devicesMuch like IDE hard disks, the SCSI ID of a SCSI hard disk is typically configuredusing jumper switches on the physical hard drive itself. Some SCSI devices act as a gateway to other devices;if this is the case, each deviceis associated with a unique Logical Unit Number (LUN). NOTE

ALinux installation is a large and complicated task;it requires a great deal of hardware andsoftware knowledge.In Chapter 3, Linux Installation and Usage, you examined theinstallation process using common hardware components and practices.This chapter examineshardware further and emphasizes hardware that is less common and more difficult to config- ure.In addition,you explore various methods for installing Linux and common installationproblems. Advanced Hardware ConfigurationSome of the hardware peripherals your system utilizes might require specialized setup andconfiguration.Chapter 2, Preparing for Linux Installation, emphasized the IDE hard diskdrive configuration,as it is the most common configuration found in home and office com- puters as of this writing.Chapter 2 also introduced the configuration of peripheral compo- nents using IRQs,I/O addresses,and DMAs.This section explores the configuration of SCSIhard disks,RAID,and common peripheral configurations seen in most computers. SCSI Hard Disk Drive ConfigurationThe Small Computer System Interface (SCSI) was designed as a way to connect multipleperipherals to the system in a scalable,high-speed manner.Recall that a SCSI device is notusually connected directly to the mainboard,but rather to a controller card,which,in turn,con- nects all devices attached to it to the mainboard.Disk devices attach to the SCSI controllercard via one cable with several connectors for the devices to plug in to.Information is thensent from device to device along this cable in a daisy-chain fashion.To prevent signals frombouncing back and forth on the cable,each end of the cable must be terminated with a devicethat stops signals from being perpetuated.This device is called a terminator.Typically,one ter- minator is on the controller card itself,as shown in the top half of Figure 7-1.Some systemsthat have several hard drives attached to one controller,however,typically place the controllerin the middle of the daisy chain,as shown in the bottom half of Figure 7-1. SCSI disk drives must be configured such that each hard disk drive can be uniquely identifiedby the system;this is accomplished by assigning a unique ID number known as a SCSI IDortarget IDto each device.Most SCSI controllers today support up to 15 devices and identifythese devices with the numbers 0 15 (one number must be reserved for the controller carditself).This SCSI ID also gives priority to the device.The highest priority device is given thenumber 7,followed by 6,5,4,3,2,1,0,15,14,13,12,11,10,9,and 8.

AdvancedInstallationChapter 7After completing this chapter,you will be able to: .Describe the types and structure of SCSI devices .Identify default IRQs,I/O addresses,and DMAs .Explain how Plug-and-Play can be used to assign configuration toperipheral devices .Explain how APM and ACPI can be used to control power to peripheraldevices .Outline the steps used to install Linux from source files on a DVD,harddisk,or network server .Understand methods used to automate the Linux installation .Install Red Hat Fedora Linux using a kickstart file .Troubleshoot the installation process

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7.True or false? Subdirectories cannot be created on a mounted floppy drive. 8.True or false? All the partitions on a hard drive share a single filesystem. 9.True or false? After filesystems are created on disk devices and those disk devices aremounted to the directory tree,there is no need for any further maintenance. 10.True or false? Quotas can restrict how many files and directories a user can create. 11.Most devices on a Linux system (such as disks,terminals,and serial ports) are repre- sented by a file on the hard disk called a(n) _________________________ file. 12.When the Linux system is first turned on,a filesystem present on the hard drive ismounted to the / directory.This is referred to as the _________________________ filesystem and contains most of the operating system files. 13.Hard disk drives come in two flavors,IDE and _________________________. 14.To create partitions after installation,you can use the _________________________ command. 15.The process of saving data from memory to the hard disk is called ______________. Chapter6243REVIEW QUESTIONS

Review Questions1.What is the traditional filesystem used on Linux? a.bfsb.ext2c.ext3d.hpfs2.If a CD-ROM drive is configured as a secondary slave,what is the name of the asso- ciated device file? a./dev/hdab./dev/hdbc./dev/hdcd./dev/hdd3.In a hard drive,data is read from disks in concentric circles called _______________. a.tracksb.sectorsc.cylindersd.blocks4.To view the size of a directory and its contents in Kilobytes,you can use the _______ command. a.pwdb.fdiskc.fsckd.du5.Using the _________________________ flag of the fsck command performs a fullfilesystem check and displays a progress line. a.-ARb.-Cfc.-ad.-A6.True or false? The type of filesystem used determines how files are managed on thephysical hard disk. 242Chapter 6LINUX FILESYSTEM ADMINISTRATION

major number The number used by the kernel to identify which device driver to call tointeract properly with a given category of hardware;hard disk drives,CD-ROMs,and videocards are all categories of hardware;similar devices share a common major number. minor number The number used by the kernel to identify which specific hardware device, within a given category,to use a driver to communicate with;see alsoMajor number. mkfs (make filesystem) command A command used to format or create filesystems. mknod command A command used to re-create a device file,provided the major number, minor number,and type (character or bock) are known. mount command A command used to mount filesystems on devices to mount point direc- tories. mount point The directory in a file structure to which something is mounted. mounting A process used to associate a device with a directory in the logical directory treesuch that users can store data on that device. partition A physical division of a hard disk drive. quota command A command used to view disk quotas imposed on a user. quotaoff command A command used to deactivate disk quotas. quotaon command A command used to activate disk quotas. quotas The limits that can be imposed on users and groups for filesystem usage. repquota command A command used to produce a report on quotas for a particular filesys- tem. root filesystem The filesystem that contains most files that make up the operating system; it should have enough free space to prevent errors and slow performance. sector The smallest unit of data storage on a hard disk;sectors are arranged into concen- tric circles called tracks and can be grouped into blocks for use by the system. soft limit A limit imposed that can be exceeded for a certain period of time. syncing The process of writing data to the hard disk drive that was stored in RAM. track The area on a hard disk that forms a concentric circle of sectors. tune2fs command A command used to modify ext2 and ext3 filesystem parameters. umount command A command used to break the association between a device and a direc- tory in the logical directory tree. Chapter6241KEY TERMS

/etc/fstab A file used to specify which filesystems to mount automatically at boot time andqueried by the mount command if an insufficient number of arguments are specified. /etc/mtab A file that stores a list of currently mounted filesystems. /proc/devices A file that contains currently used device information. bad blocks The areas of a storage medium unable to store data properly. block The unit of data commonly used by filesystem commands;a block can contain sev- eral sectors. block devices The storage devices that transfer data to and from the system in chunks ofmany data bits by caching the information in RAM;they are represented by block device files. character devices The storage devices that transfer data to and from the system one databit at a time;they are represented by character device files. cylinder A series of tracks on a hard disk that are written to simultaneously by the mag- netic heads in a hard disk drive. device file A file used by Linux commands that represents a specific device on the system; these files do not have a data section and use major and minor numbers to reference the properdriver and specific device on the system,respectively. df (disk free space) command A command that displays disk free space by filesystem. du (directory usage) command A command that displays directory usage. edquota command A command used to specify quota limits for users and groups. fdisk command A command used to create,delete,and manipulate partitions on hard disks. filesystem The organization imposed on a physical storage medium that is used to managethe storage and retrieval of data. filesystem corruption The errors in a filesystem structure that prevent the retrieval of storeddata. formatting The process in which a filesystem is placed on a disk device. fsck (filesystem check) command A command used to check the integrity of a filesystemand repair damaged files. fuser command A command used to identify any users or processes using a particular fileor directory. hard disk quotas The limits on the number of files,or total storage space on a hard diskdrive,available to a user. hard limit A limit imposed that cannot be exceeded. 240Chapter 6LINUX FILESYSTEM ADMINISTRATION