Basic Disk Drives

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CHAPTER 9

• Basic Disk Drives

2
Chapter Overview

• Floppy Disk Drives
• Hard Disk Drives

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The Basics of Floppy Disk Drives

• In 1972, IBM developed the First floppy disk
  drives for its system 370 machines. these drives
  used 8-inch floppy disk.
• When IBM introduced the personal computer (PS)
  in 1981, it came standard with a 5.25-inch
  floppy.
• Todays 3.5-inch floppy disk are made of
  flexible plastic and coated with a magnetic
  material.

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• Major differences between the 5.25-inch and
  3.5-inch
• Physical size.
• 5.25-inch has a slot connector.
• 3.5-inch has a pin connector.
• Different power plug and voltages.

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Keeping a Floppy Disk Drive Running

• Schedule monthly cleanings.
• Check the floppy disk first for data errors or
  write protection.
• Check complementary metal-oxide semiconductor
  (CMOS) settings.
• Check or change the floppy disk drive cable.
• Change the floppy disk drive controller.
• Replace the floppy disk drive as needed.

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Errors Caused by the Floppy Disk

• First , make sure the disk is not write
  protected. The hole on the right top corner
  should be closed.
• Try another disk.
• Try a new ( formatted) disk.
• Try someone elses disk , one that is known to
  work on another computer.
• Try going to MS-DOS and reading a directory
  using the DIR command.
• POST will return FDD controller failure or
  drive not ready errors in the event of a loose
  data cable or power plug.

I/O card with floppy disk controller
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Hard Disk Drives

• Hard disk drives are mass storage devices.
• The First hard disk drives were small in capacity
  , physically and expensive.
• In 1981, IBM introduced the XT computer with a
  10-MB hard drive.
• Today, a new hard disk drive can fit in your
  pocket and hold over 40 GB of data.

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Physical Characteristics

• The First form of PC mass storage was the
  magnetic tape drive.
• The typical cassette drive cartridge was easily
  damaged.
• Gaining access to the data was slow due to the
  way data is organized on tape.
• Tapes were hundreds of feet long, and users
  often had to run the entire length of the tape to
  find the data they were seeking.
• The original concept behind the hard disk drive
  was to provide a storage medium that hold large
  amounts of data and allowed fast random access to
  that data.
• The First IBM hard disk drives were code-named
  Winchester.
• The PC-XT was the First personal computer to
  include a hard disk.
• Hard disk drives are composed of several platters
  , matched to a collection of R/W heads and an
  actuator.
• The distance between the heads and the disk
  surface is less than the thickness of a
  fingerprint.

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Storing Data

• Data is stored using binary code.
• 1s and 0s are stored in computers memory as
  electrical impulses.
• On magnetic media , the 1s and 0s can be stored
  as either magnetic or nonmagnetic areas on the
  drive surface.
• The 0s and 1s of the binary code are stored in
  terms of flux reversals.
• Flux reversals are actually the transitions
  between magnetized and nonmagnetized positions on
  the hard drive surface.

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Frequency Modulation ( FM)

• FM technology is based on timing.
• To differentiate a 1 from a 0, it measures the
  time the drive head spends in a magnetized state.
• The name "frequency modulation" comes from the
  fact that the num of reversals is doubled for
  ones compared to that for zeros. This can be seen
  in the patterns that are created if you look at
  the encoding pattern of a stream of ones or
  zeros. A byte of zeroes would be encoded as
  "RNRNRNRNRNRNRNRN", while a byte of all ones
  would be "RRRRRRRRRRRRRRRR". As you can see, the
  ones have double the frequency of reversals
  compared to the zeros hence frequency modulation
  (meaning, changing frequency based on data
  value).
• FM encoding write waveform for the byte
  "10001111".Each bit cell is depicted as a blue
  rectangle with a pink line representingthe
  position where a reversal is placed, if
  necessary, in the middle of the cell.

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Storing Data cont

• MFM uses the previous data bit to indicate
  whether the current bit is a 1 or a 0.
• Reduce the timing by considering not just the
  current bit but also the one before it .
• IN RLL It considers groups of several bits
  instead of encoding one bit at a time

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Physical Characteristics
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Actuator Arms

• Hold read/write (R/W) heads in place
• Must deliver speed and accuracy
• Use one of the following technologies
• The stepper motor (older) had many disadvantages.
• The voice coil motor (newer) uses the head for
  mapping.
• Might be damaged by head-to-disk interference
  (HDI), or head crash

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Stepper Motor

• hard disk drives used a stepper motor to control
  the movement of the heads over the surface of the
  platters.
• A stepper motor actuator. The motor moves in
  steps, which you can feel ifyou move the motor
  shaft by hand.

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voice coil motor

• The actuator in a modern hard disk uses a device
  called a voice coil to move the head arms in and
  out over the surface of the platters, and a
  closed-loop feedback system called a servo system
  to dynamically position the heads directly over
  the data tracks.
• When current is fed to the coil, an
  electromagnetic field is generated that causes
  the heads to move in one direction

Head-to-disk interface(HDI) or head crash these
terms describe the contact that sometimes occurs
between the surface of the disk and the R/W head.
Check pages 192,193 the disadvantages of each
type
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Geometry
Watch video
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Geometry the geometry of a hard drive is the
organization of data on these platters. Geometry
determines how and where data is stored on the
surface of each platter. Heads the number of
heads is relative to the total number of sides of
all the platters used to store data. Cylinder
data is stored in circular paths on the surface
of each platter. Each path is called a track,.
There are hundreds of tracks on the surface of
each platter. A set of tracks through each
platter is called a cylinder. Sector per track A
hard disk drive is cut into tens of thousands of
small arcs, each arc is called a sector and holds
512 bytes of data.
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• CHS values cylinder, heads, and sectors per
  track are known as CHS values. The capacity of
  any hard disk drive can be determined from these
  three values.
• The maximum CHS values are
• 1024 cylinders.
• 16 heads
• 63 sectors per track
• 512 bytes per sector

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Hard Disk Drive Types

• ST-506
• Enhanced Small Device Interface (ESDI)
• Integrated Device Electronics/Enhanced Integrated
  Drive Electronics (IDE/EIDE)
• Small Computer System Interface (SCSI)

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ST506

• The first hard disk drive for personal
  computers, introduced in 1979 by Seagate. It was
  used in drives of 40MB and less and transferred
  data at 625 Kbytes/sec, using the MFM encoding
  method.
• ST-506 uses a 34-connector control cable and
  20-connector data cable.

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Enhanced Small Device Interface (ESDI)

• The first attempt at improving the original
  ST-506/ST-412 hard disk interface was the
  Enhanced Small Device Interface or ESDI. ESDI was
  developed in the mid-1980s by Maxtor.
• ESDI improved on ST-506/ST-412 in several ways.
  It moved some drive controller functions to the
  hard disk from the controller card, eliminating
  some of the reliability problems associated with
  its predecessor.

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IDE/EIDE

• The IDE ( integrated device electronics) drive
  arrived on the early 1990s.
• It supports the ST-506 standard command set, and
  it limited controller function build directly on
  the drive's logic board.
• Enhanced IDE ( EIDE) adds a number of
  improvements to the standard IDE drives,
  including
• Increased data throughput.
• Support of storage devices other than hard disk
  drive.
• Up to four IDE devices instead of just two.
• Support for hard disk drives larger than 528 MB.

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SCSI

• SCSI( small computer system interface) .it is
  most strong of the hard disk drive interfaces,
  and it is popular on network servers and
  high-performance workstations.
• It is only one that allows both internal and
  external connections on the same adapter,
  includes a hard disk, CDROM scanners and tape
  drives.

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Installation and Setup the Five Steps

1. Physical installation and cabling
2. CMOS setup
3. Low-level formatting
4. Partitioning
5. High-level formatting

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Physical Installation and Cabling
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Setting the System CMOS for the Hard Disk
DriveCMOS Main Screen
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Setting the System CMOS for the Hard Disk
DriveHard Drive Setup Screen
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Low-Level Formatting

• Creates and organizes sectors
• Sets the proper interleave
• Establishes the boot sector

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Preparing the New Drive

• Create a bootable disk with formatting utilities.
• Create a Microsoft Windows 98 startup disk.
• Use the bootable disk to partition and format the
  new drive.

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Partitioning
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High-Level Formatting

• FORMAT.COM does the following
• Creates and configures the file allocation tables
  (FATs)
• Creates the root directory
• The FAT tracks which part of a file is stored on
  which sector.
• FAT32 uses disk space more efficiently.

HW4 What is the difference between the Low-level
Formatting and High-Level Formatting?
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High-Level Formatting (Cont.)

• Consider several factors before using FAT32.
• You should not use FAT32 on dual boot systems
  shared by operating systems (OSs) that do not
  support FAT32.
• FAT32 partitions that are shared can be read
  across the network.
• FAT32 does not support compression.
• You should not use disk utilities that are not
  made for FAT32.

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Fragmentation and Compression

• A hard disk can become fragmented over time.
• MS-DOS, Microsoft Windows 95, Microsoft Windows
  98, and Microsoft Windows Me have defragmentation
  programs.
• Disk compression eliminates wasted cluster space.

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Maintaining a Hard Disk Drive

• Perform comprehensive, regularly scheduled
  backups.
• Save a copy of the boot sector and partition
  table information.
• Have tools on hand for hard disk repairs.
• Use only disk tools certified for the hard disk
  drive and the OS.

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Common Errors and Troubleshooting Utilities

• Errors
• Abort, Retry, Fail
• Connectivity problems
• Lost boot and partition information
• CMOS errors
• Utilities
• Scandisk
• SCSI BIOS disk utility

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Chapter Summary

• Floppy disk drive technology has changed little
  over the years.
• Floppy disk drives fail more often than any other
  computer component.
• Installing a hard disk drive requires you to
  partition the drive, set the CMOS settings, and
  format the drive.
• The fdisk utility is used to create partitions.
• The geometry (CHS values) of a hard disk drive
  determines its storage capacity.
• Partition types include primary, extended,
  logical, and active.
• The active partition is used to initialize the
  OS.