Transcript Document 7484265

CHAPTER 9
Basic Disk Drives
Chapter Overview
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Floppy Disk Drives
Hard Disk Drives
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.
 Today’s 3.5-inch floppy disk are made of flexible plastic and coated with a
magnetic material.
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.
Keeping a Floppy Disk Drive Running
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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.
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 else’s 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
Hard Disk Drives
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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.
Physical Characteristics
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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.
Storing Data
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Data is stored using binary code.
1s and 0s are stored in computer’s 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.
Frequency Modulation ( FM)
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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 representing
the position where a reversal is placed, if necessary, in the middle of the
cell.
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
Physical Characteristics
Actuator Arms
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Hold read/write (R/W) heads in place
Must deliver speed and accuracy
Use one of the following technologies:
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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
Stepper Motor
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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 if
you move the motor shaft by hand.
voice coil motor
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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
Geometry
Watch video
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.
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
Hard Disk Drive Types
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ST-506
Enhanced Small Device Interface (ESDI)
Integrated Device Electronics/Enhanced
Integrated Drive Electronics (IDE/EIDE)
Small Computer System Interface (SCSI)
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 20connector data cable.
Enhanced Small Device Interface (ESDI)
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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.
IDE/EIDE
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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.
SCSI
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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,
CD–ROM scanners and tape drives.
Installation and Setup: the Five Steps
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Physical installation and cabling
CMOS setup
Low-level formatting
Partitioning
High-level formatting
Physical Installation and Cabling
Setting the System CMOS for the
Hard Disk Drive–CMOS Main Screen
Setting the System CMOS for the Hard
Disk Drive–Hard Drive Setup Screen
Low-Level Formatting
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Creates and organizes sectors
Sets the proper interleave
Establishes the boot sector
Preparing the New Drive
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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.
Partitioning
High-Level Formatting
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FORMAT.COM does the following:
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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?
High-Level Formatting (Cont.)
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Consider several factors before using FAT32.
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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.
Fragmentation and Compression
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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.
Maintaining a Hard Disk Drive
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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.
Common Errors and Troubleshooting
Utilities
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Errors
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Abort, Retry, Fail
Connectivity problems
Lost boot and partition information
CMOS errors
Utilities
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Scandisk
SCSI BIOS disk utility
Chapter Summary
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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.