Introduction to Hard Drives

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Chapter 6

• Introduction to Hard Drives

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You Will Learn

• How data is stored on a hard drive
• How to use DOS and Windows commands to manage
  data on a hard drive
• How to identify various types of hard drives and
  understand advantages of each
• How to manage a hard drive to optimize its
  performance
• How to compare different removable drives

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Hard Drive Technology
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Hard Drive Technology
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Hard Drive Technology

• Methods used to adjust for smaller tracks closer
  to center of platter
• Write precompensation
• Reduced write current

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Integrated Device Electronics (IDE) Technology

• A hard drive whose disk controller is integrated
  into the drive
• Eliminates need for controller cable
• Increases speed
• Reduces price
• OS does not communicate directly with the IDE
  drive OS passes requests to the drive
  controller, which is responsible for keeping up
  with where and how data is stored on a drive
• Most system boards provide one or two IDE
  connections directly on system board

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Hardware Subsystem with an IDE Hard Drive
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Tracks and Sectors on an IDE Drive

• MFM and RLL technologies use either 17 or 26
  sectors per track
• Wastes drive space
• Number of bytes a track can hold is determined by
  centermost track

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Tracks and Sectors on an IDE Drive

• Use zone bit recording
• Tracks near center have smallest number of
  sectors per track
• Number of sectors increases as tracks get larger
• Have 512 bytes per sector for every sector on the
  drive

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Zone Bit Recording
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Enhanced IDE (EIDE) Drives

• Support newer, faster drive standard that allows
  systems to recognize drives larger than 504 MB
  and to handle up to four devices on the same
  controller

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ANSI Standards for Hard Drives
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SCSI (Small Computer Systems Interface) Technology

• Provides a standard for communication between a
  subsystem of peripheral devices and the system
  bus
• Most SCSI drives are IDE drives

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SCSI Technology
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Differing SCSI Standards

• General categories
• Narrow (8 bits)
• Wide (16 bits)
• Ways a SCSI cable can be built
• Single-ended
• Differential
• Three major standards
• SCSI-1 (Regular SCSI)
• SCSI-2 (Fast SCSI)
• SCSI-3 (Ultra SCSI)

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Summary of Different SCSI Standards
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Sample Configuration of a SCSI Subsystem
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Other Variations of SCSI Hardware and Software

• Termination
• Device drivers
• Host adapter issues

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Termination

• Prevents an echo effect of power at the end of a
  SCSI chain resulting in interference with the
  data transmission
• Several ways to terminate power
• Types of terminators
• Passive
• Active
• Forced perfect (more expensive and more reliable)

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Termination
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Termination
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Device Drivers

• Advanced SCSI Programming Interface (ASPI)
• Common Access Method (CAM)

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Host Adapter Issues

• Compare installation procedures and options

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Comparing SCSI Hard Drives and EIDE Hard Drives

• SCSI costs more than EIDE but gives better
  performance
• SCSI provides faster data transfer
• SCSI bus supports multitasking EIDE processes
  data from one I/O device at a time
• SCSI host adapter allows connection to non-SCSI
  devices
• Without SCSI, if two IDE drives are on the same
  adapter, only one can be busy at a time

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Other Types of Hard Drive Interfaces

• IEEE 1394
• Also known as FireWire and i.Link
• Uses serial transmission of data
• Popular with multimedia and home entertainment
  applications
• Fibre Channel
• Designed for use in high-end systems that have
  multiple hard drives (competes with SCSI)
• Faster than SCSI when more than 5 hard drives are
  strung together for massive secondary storage
• Too expensive and has too much overhead for
  desktop PC or workstation

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How a Hard Drive Is Logically Organized to Hold
Data

• Steps in preparing a hard drive to hold data
• Low-level format
• Partitioning the hard drive
• High-level format

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Hard Drive Partition Table
continued
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Hard Drive Partition Table
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Logical Drives