Mass Storage Devices

Dept of IT | III YEAR | V SEMESTER IT E51 | COMPUTER HARDWARE AND TROUBLESHOOTING | UNIT 4
1 |Prepared By : Mr. PRABU.U/AP |Dept. of Computer Science and Engineering | SKCET |
UNIT IV
Mass Storage Devices Floppy disk and drive – Hard disk and drive – MFM and RLL
recording standards – CD Technology – DVD technology – pen drives – tape drives
4.1 FLOPPY DISK AND DRIVE
 A floppy disk drive (FDD), or floppy drive, is a hardware device that reads data
storage information.
 It was invented in 1967 by a team at IBM and was one of the first types of
hardware storage that could read/write a portable device.
 FDDs are used for reading and writing on removable floppy discs.
 Floppy disks are now outdated, and have been replaced by other storage devices
such as USB and network file transfer.
4.1.1 The Basics
 Spins at 360 rpm.
 Read/Write heads contact the disk surface – so don’t pull a floppy while the
activity light is on.
 Floppy disks, initially as 8-inch (200 mm) media and later in 5¼-inch (133 mm)
and 3½-inch (90 mm) sizes.
 Connected with 34-pin ribbon cable.
4.1.2 Floppies come in three basic sizes
 8-inch:The first floppy disk design, invented by IBM in the late 1960s and used
in the early 1970s.
 It first a read-only format and then as a read-write format.
 The typical desktop/laptop computer does not use the 8-inch floppy disk.
 5-inch: The common size for PCs made before 1987 and the predecessor to the
8-inch floppy disk.
 This type of floppy is generally capable of storing between 100K and 1.2MB
(megabytes) of data.
 The most common sizes are 360K and 1.2MB.
 3-inch: Floppy is something of a misnomer for these disks, as they are encased in
a rigid envelope.
 Despite their small size, microfloppies have a larger storage capacity than their
cousins -- from 400K to 1.4MB of data.
 The most common sizes for PCs are 720K (double-density) and 1.44MB (high-
density).
4.1.3 Parts of a Floppy Disk Drive
1. The Disk
A floppy disk is a lot like a cassette tape:

 Both use a thin plastic base material coated with iron oxide. This oxide is a
ferromagnetic material, meaning that if you expose it to a magnetic field it is
permanently magnetized by the field.
 Both can record information instantly.
 Both can be erased and reused many times.
 Both are very inexpensive and easy to use.
2. The Drive
The major parts of a FDD include:
 Read/Write Heads: Located on both sides of a diskette, they move together on
the same assembly. The heads are not directly opposite each other in an effort to
prevent interaction between write operations on each of the two media surfaces.
The same head is used for reading and writing, while a second, wider head is
used for erasing a track just prior to it being written. This allows the data to be
written on a wider "clean slate," without interfering with the analog data on an
adjacent track.
 Drive Motor: A very small spindle motor engages the metal hub at the center of
the diskette, spinning it at either 300 or 360 rotations per minute (RPM).
 Stepper Motor: This motor makes a precise number of stepped revolutions to
move the read/write head assembly to the proper track position. The read/write
head assembly is fastened to the stepper motor shaft.
 Mechanical Frame: A system of levers that opens the little protective window
on the diskette to allow the read/write heads to touch the dual-sided diskette
media. An external button allows the diskette to be ejected, at which point the
spring-loaded protective window on the diskette closes.
 Circuit Board: Contains all of the electronics to handle the data read from or
written to the diskette. It also controls the stepper-motor control circuits used to
move the read/write heads to each track, as well as the movement of the
read/write heads toward the diskette surface.
4.1.4 Internal parts of a 3½-inch floppy disk
1) A hole that indicates a high-capacity disk.
2) The hub that engages with the drive motor.
3) A shutter that protects the surface when removed from the drive.
4)The plastic housing.
5) A polyester sheet reducing friction against the disk media as it rotates within the
housing.
6) The magnetic coated plastic disk.
7) A schematic representation of one sector of data on the disk; the tracks and sectors
are not visible on actual disks.
8) The write protection tab (unlabeled) is upper left.
4.1.5 Types of Floppies
1. Zip disks - 100 MB, 250 MB or 750 MB
2. HiFD disks - 200MB or 720MB
3. SuperDisks - 120 MB or 240 MB

 4-wire Power cable.
 5.25 inch drives require a +12 volt and a +5 volt supply
 Current 3.5 inch drives only require a +5 volt supply.
Floppy Drive Size Tracks/Side Sectors/Track Capacity
5 1/4" DD 40 9 360KB
5 1/4" HD 80 15 1.2MB
3 1/2" DD 80 9 720KB
3 1/2" HD 80 18 1.44MB
3 1/2" ED 80 36 2.88MB
 DD = Double Density
 HD = High Density
 ED = Extended Density
4.1.6 Writing Data on a Floppy Disk
The following is an overview of how a floppy disk drive writes data to a floppy disk.
Reading data is very similar. Here's what happens:
1. The computer program passes an instruction to the computer hardware to
write a data file on a floppy disk, which is very similar to a single platter in a hard
disk drive except that it is spinning much slower, with far less capacity and
slower access time.
2. The computer hardware and the floppy-disk-drive controller start the motor in
the diskette drive to spin the floppy disk.
The disk has many concentric tracks on each side. Each track is divided into
smaller segments called sectors, like slices of a pie.
3. A second motor, called a stepper motor, rotates a worm-gear shaft (a
miniature version of the worm gear in a bench-top vise) in minute increments
that match the spacing between tracks.
The time it takes to get to the correct track is called "access time." This stepping
action (partial revolutions) of the stepper motor moves the read/write heads
like the jaws of a bench-top vise. The floppy-disk-drive electronics know how
many steps the motor has to turn to move the read/write heads to the correct
track.
4. The read/write heads stop at the track. The read head checks the prewritten
address on the formatted diskette to be sure it is using the correct side of the
diskette and is at the proper track. This operation is very similar to the way a
record player automatically goes to a certain groove on a vinyl record.
5. Before the data from the program is written to the diskette, an erase coil (on the
same read/write head assembly) is energized to "clear" a wide, "clean slate"
sector prior to writing the sector data with the write head. The erased sector is
wider than the written sector -- this way, no signals from sectors in adjacent
tracks will interfere with the sector in the track being written.
6. The energized write head puts data on the diskette by magnetizing minute,
iron, bar-magnet particles embedded in the diskette surface, very similar to the
technology used in the mag stripe on the back of a credit card. The magnetized
particles have their north and south poles oriented in such a way that their
pattern may be detected and read on a subsequent read operation.

7. The diskette stops spinning. The floppy disk drive waits for the next command.
On a typical floppy disk drive, the small indicator light stays on during all of the above
operations.
4.1.7 Floppy Disk Drive Facts
Here are some interesting things to note about FDDs:
 Two floppy disks do not get corrupted if they are stored together, due to the low
level of magnetism in each one.
 In your PC, there is a twist in the FDD data-ribbon cable -- this twist tells the
computer whether the drive is an A-drive or a B-drive.
 Like many household appliances, there are really no serviceable parts in today's
FDDs. This is because the cost of a new drive is considerably less than the hourly
rate typically charged to disassemble and repair a drive.
 If you wish to redisplay the data on a diskette drive after changing a diskette, you
can simply tap the F5 key (in most Windows applications).
 In the corner of every 3.5-inch diskette, there is a small slider. If you uncover the
hole by moving the slider, you have protected the data on the diskette from being
written over or erased.
 Floppy disks, while rarely used to distribute software (as in the past), are still
used in these applications:
 in some Sony digital cameras
 for software recovery after a system crash or a virus attack
 when data from one computer is needed on a second computer and the
two computers are not networked
 in bootable diskettes used for updating the BIOS on a personal computer
 in high-density form, used in the popular Zip drive
4.2 HARD DISK AND DRIVE
 A hard disk drive (sometimes abbreviated as "Hard drive," "HD", or "HDD") is a
data storage device.
 The hard disk was first introduced on September 13, 1956
 It consists of one or more platters inside of an air-sealed casing.
 they offered 5-megabyte capacity.
 During the mid-1990s the typical hard disk drive for a PC had a capacity of about
1 gigabyte.
 As of December 2014, desktop hard disk drives typically had a capacity of 500 to
4000 gigabytes, while the largest-capacity drives were 8 terabytes.
4.2.1 Working
 Hard drive consists of the following components: the head actuator, read/write
actuator arm, read/write head, spindle, and platter.
 On the back of a hard drive is a circuit board called the disk controller
 Data sent to and from the hard drive is interpreted by the disk controller, which
tells the hard drive what to do and how to move the components within the
drive.
 When the operating system needs to read or write information, it examines the
hard drive's File Allocation Table (FAT) to determine file location and available
areas.

 Once this has been determined, the disk controller instructs the actuator to move
the read/write arm and align the read/write head.
 Because files are often scattered throughout the platter, the head needs to move
to different locations to access all information.
 If the computer needs to read information from the hard drive, it would read the
magnetic polarities on the platter.
 One side of the magnetic polarity is 0 and the other is 1.
 Reading this as binary data, the computer can understand what the data is on the
platter.
 For the computer to write information to the platter, the read/write head aligns
the magnetic polarities, writing 0's and 1's that can be read later.
4.2.2 Preparing a Disk Drive for Data Storage
It involves three steps:
 Low-Level formatting (LLF)
 Partitioning
 High-level formatting (HLF)
Low Level Formatting
 Low level formatting marks the tracks and sectors of the disk.
 A sector is a small section of a track that stores 512 Bytes of information
Partitioning
 Partitioning a disk is the act of defining areas of the disk for an operating system
to use.
 Partitioning is required because a hard disk is designed to be used with more
than one operating system.
 Partitioning enables a single hard disk drive to run more than one type of
operating system (dual boot), or it can enable a single operating system to use
the disk as several volumes or logical drives.
 You decide you want to break the 10GB space into three logical partitions: one
with 5GB of space, one with 3GB, and one with 2GB.
 The operating systems will logically view these three partitions as three separate
drives and gives them separate drive letters C:, D:, and E:.
 Physically all you have is one hard drive with three logical drives.
 Hard drive partitions must always begin at C:; because the A: and B: drives are
reserved for floppies.

High Level Formatting
 Formatting also creates the root directory. (C:)
 If the disk is to be made bootable, COMMAND.COM and two system files (io.sys
and msdos.sys) must be in the root directory of the bootable drive.
4.2.3 Hard Disk Characteristics
 Capacity, usually quoted in gigabytes. (older hard disks used to quote their
smaller capacities in megabytes)
 Physical size, usually quoted in inches:
 Almost all hard disks today are of either the 3.5" or 2.5" varieties, used in
desktops and laptops, respectively. 2.5" disks are usually slower and have
less capacity but use less power and are more tolerant of movement.
 Reliability, usually given in terms of mean time between failure (MTBF):
 SATA 1.0 disks support speeds up to 10,000 RPM and MTBF levels up to 1
million hours under an eight-hour, low-duty cycle.
 Fibre Channel (FC) disks support up to 15,000 RPM and an MTBF of 1.4
million hours under a 24-hour duty cycle.
 Number of I/O operations per second:
 Modern disks can perform around 50 random access or 100 Sequential
access operations per second.
 Power consumption (especially important in battery-powered laptops).
 G-shock rating (surprisingly high in modern disks).
 Transfer Rate:
 Inner Zone: from 44.2 MB/s to 74.5 MB/s.
 Outer Zone: from 74.0 MB/s to 111.4 MB/s.
 Random access time: from 5 ms to 15 ms.
4.2.4 Disk Families used in Personal Computers
 Notable disk families include:
 MFM (Modified Frequency Modulation) disks required that the controller
electronics be compatible with the disk electronics.
 RLL (Run Length Limited) disks were named after the modulation technique that
made them an improvement on MFM. They required large cables between the

controller in the PC and the hard disk, the disk did not have a controller, only a
modulator/demodulator.
 ESDI (Enhanced Small Disk Interface) was an interface developed by Maxtor to
allow faster communication between the PC and the disk than MFM or RLL.
 Integrated Drive Electronics (IDE) was later renamed to ATA, and then PATA.
The name comes from the way early families had the hard disk controller
external to the disk. Moving the hard disk controller from the interface card to
the disk helped to standardize interfaces, including reducing the cost and
complexity.
 SCSI (Small Computer System Interface) was an early competitor with ESDI,
originally named SASI for Shugart Associates. SCSI disks were standard on
servers, workstations, and Apple Macintosh computers through the mid-90s, by
which time most models had been transitioned to IDE (and later, SATA) family
disks.
 SATA (Serial ATA). The SATA data cable has one data pair for differential
transmission of data to the device, and one pair for differential receiving from
the device, just like EIA-422. That requires that data be transmitted serially. The
same differential signaling system is used in RS485, Local Talk, USB, Fire wire,
and differential SCSI.
 SAS (Serial Attached SCSI). The SAS is a new generation serial communication
protocol for devices designed to allow for much higher speed data transfers and
is compatible with SATA. SAS uses serial communication instead of the parallel
method found in traditional SCSI devices but still uses SCSI commands for
interacting with SAS
 EIDE was an unofficial update (by Western Digital) to the original IDE standard,
with the key improvement being the use of DMA to transfer data between the
disk and the computer, an improvement later adopted by the official ATA
standards. DMA is used to transfer data without the CPU or program being
responsible to transfer every word. That leaves the CPU/program/operating
system to do other tasks while the data transfer occurs.
4.3 MFM AND RLL RECORDING STANDARDS
 Modified Frequency Modulation (MFM)
 Modified frequency modulation (MFM) is a method of encoding digital data on
magnetic media.
 Run-length limited (RLL) coding scheme used to encode the actual data-bits on
most floppy disks.
 MFM was used with early hardware, including Control Program for
Microcomputers (CP/M), IBM compatible PCs and Amiga PCs.
 MFM is a modification to the original FM (frequency modulation) scheme for
encoding data on single-density floppy disks and some early hard disk drives.
 MFM was used on 3.5-inch and 5.25-inch disks, or floppy's, with data transfer
rates (DTR) of 250 to 500 kbps,
 MFM ST-506 hard disks up to five Mbps.
 MFM is now with the exception of 1.44 MB floppy disks.
 It was also known as “double density.”
 The 1 bit is characterized by a magnetic transition, which is usually a positive
voltage.
 A 0 bit does not have a magnetic transition and is generally a negative voltage.

 Newer standard interfaces, like Small Computer System Interface (SCSI) and
Enhanced Integrated Drive Electronics (EIDE), support faster DTRs.
MFM has five basic encoding rules, as follows:
 Flux transitions are never at a 0 bit's midpoint.
 Flux transitions are always at a 1 bit's midpoint.
 Flux transitions are never at a 1 bit's starting point or at a 1 bit's endpoint.
 The run length limit is cells of two bits, which facilitates continuous flux
reversals between two neighbouring 0 bits.
 The space following the last data bit and the lead-in just before the first data bit
are recorded with clocking bits (0s).
RLL
 Today’s most popular encoding scheme for hard disks, called Run Length
Limited,
 IBM invented RLL encoding and first used the method in many of its mainframe
disk drives.
 During the late 1980s, the PC hard disk industry began using RLL encoding
schemes to increase the storage capabilities of PC hard disks.
 Today, virtually every drive on the market uses some form of RLL encoding.
 Run length limited (RLL) encoding schemes include a collection of encodings that
can be categorized by two parameters:
 run length and run limit.
 The run length is the minimum number of cells (potential transitions) that can
occur between transitions and
 the run limit is the maximum number of cells (potential transitions) that can
occur between transitions.
 It is actually possible to consider FM encoding to be RLL (0,1) and MFM encoding
to be RLL (1, 3).
 RLL codes are defined by four main parameters: m, n, d, k.
 The first two m/n refer to the rate of the code,
 While the remaining two specify the minimum d and maximum k number of
zeroes between consecutive ones.
4.4 CD TECHNOLOGY
 Compact disc (CD) is a digital optical disc data storage format.
 The format was originally developed to store and play only sound recordings
but was later adapted for storage of data (CD-ROM).
 Standard CDs have a diameter of 120 millimetres (4.7 in) and can hold up to
about 80 minutes of uncompressed audio or about 700 MB of data.
 The Mini CD has various diameters ranging from 60 to 80 millimetres (2.4 to
3.1 in).
 Uses Digital Technology to store data in binary values of Zero and One.
 Uses “Pits” and “Lands” to signify binary values.
 A land is reflective and reflects the laser into a sensor to register it as 1. The
light hits a pit, it shatters and no reflection is received, thus a 0 is registered.
 CD’s Read at a Constant Linear Velocity (CLV).
 Capable of Storing Large Amounts of Data (up to 700MB).

4.4.1 History
1980: The first Compact Disk player is produced by Sony/Phillips.
1982: The first Compact Disk is manufactured for sale, Billy Joel’s “52nd Street”
1984: First portable Compact Disk players enter the market followed by car CD players
shortly after.
1985: Sony/Philips announce the standard for compact disc storage of computer data,
the CD-ROM.
1987: Video CD format is designed.
1991: CD-R (Compact Disk Recordable) technology is introduced as a new storage
technology.
4.4.2 Types Of Compact Disks
CD Audio – The first type of CD that was available. This allows for the storage of digital
audio. These are playable in all current CD drives and car audio systems including DVD
players.
CD-ROM – Computer Data is stored on these units such as games, applications, and
other files. Only readable on computers.
CD-R – Allows users to write data once to a recordable Compact Disk. Cannot be re-
written and can be read in all current players depending on wither the disk holds Audio
or Data.
CD-RW – Users Can Write and Re-Write these special disks. However because of the
disk format, they cannot be read in Audio CD players or DVD players.
 Sector
 2,048 bytes for data discs
 2,352 bytes for audio discs
 Track
 A single (logical) collection of data on the disc
 Up to 99 tracks on a CD
Capacities of Compact Disc types
Type Sectors
Data max size Audio max size Time
(MB) (MB) (MB) (MB) (min)
8 cm 94,500 193.536 ≈ 184.6 222.264 ≈ 212.0 21
650 MB 333,000 681.984 ≈ 650.3 783.216 ≈ 746.9 74
700 MB 360,000 737.280 ≈ 703.1 846.720 ≈ 807.4 80
800 MB 405,000 829.440 ≈ 791.0 952.560 ≈ 908.4 90
900 MB 445,500 912.384 ≈ 870.1 1,047.816 ≈ 999.3 99
Transfer Speed Megabytes/s Megabits/s
1x 0.15 1.2
2x 0.3 2.4
4x 0.6 4.8
8x 1.2 9.6

10x 1.5 12.0
12x 1.8 14.4
20x 3.0 24.0
32x 4.8 38.4
36x 5.4 43.2
40x 6.0 48.0
48x 7.2 57.6
50x 7.5 60.0
52x 7.8 62.4
4.4.3 Main Physical Parameters
 The main parameters of the CD (taken from the September 1983 issue of the
audio CD specification) are as follows:
 Scanning velocity: 1.2–1.4 m/s (constant linear velocity) – equivalent to
approximately 500 rpm at the inside of the disc, and approximately 200 rpm at
the outside edge. (A disc played from beginning to end slows down during
playback.)
 Track pitch: 1.6 μm
 Disc diameter 120 mm
 Disc thickness: 1.2 mm
 Inner radius program area: 25 mm
 Outer radius program area: 58 mm
 Center spindle hole diameter: 15 mm
 A polycarbonate disc layer has the data encoded by bumps.
 A shiny layer reflects the laser.
 A layer of lacquer protects the shiny layer.
 Artwork is the screen printed on the top of the disc.
 A laser beam reads the CD & is reflected back to sensor, which converts it into
electronic data.
4.5 DVD TECHNOLOGY
 DVD stands for Digital Versatile/Video Disc.
 It is an optical disc storage media format.
 Invented and developed by Philips, Sony, Toshiba and Panasonic in 1995.
 It offers higher storage capacity than CD's while having the same dimensions.
4.5.1 History
1996: Digital Versatile Disk (DVD) technology is introduced.
1997: DVD’s and DVD players begin to enter the market.
1998: DVD Recordable systems invented and begin to enter the market.
2000: DVD movies become mainstream and replace analog.
4.5.2 Layers
1. Single Side, Single Layer - 4.7 GB of data capacity
2. Single Side, Dual Layer - 8.5 GB on one side additional 3.8 GB on the second layer
3. Double Side, Single Layer - 9.4 GB (4.7 on each side)
4. Double Side, Dual Layer - Maximum capacity of 17GB(8.5 GB on each side)

DVD type Name
Single sided, single layer DVD-5
Single sided, dual layer DVD-9
Double sided, single layer DVD-10
Double sided, dual layer DVD-18
4.5.3 Types
There are 2 types of DVD.
1 DVD-video
2 DVD-ROM
DVD video is used to store movies on the disc. DVD ROM is used to store computer
based software and data.
Specification DVD CD-ROM
Diameter(mm) 120 120
Disk thickness (mm) 1.2 1.2
Substrate thickness (mm) 0.6 1.2
Track Pitch (nm) 740 1600
Minimum pit size(nm) 400 830
Wavelength(nm) 640 780
Single layer capacity 4.7 GB 650 MB
4.5.4 Formats
The set of accepted standards for DVDs are also referred to as books similar to
CDs. DVD technology is defined by a set of 5 books labelled A through E that relate to
different applications.
 Book A defines the format and approach used for DVD-ROM (programs and data)
 Book B defines DVD video
 Book C defines DVD audio
 Book D defines DVD-WO (Write Once)
 Book E defines DVD-E (Erasable or re-writable) and DVD RAM.
DVD-ROM
 DVD- Rom is the computer counterpart and is similar to a CD.
 The DVD-ROM drive can play all type of disks.
 It can also play video that is digitized and saved in Windows-compatible formats
such as AVI, MOV and the other streaming media formats such as Windows
media and Real media.
DVD-Video
 DVD-Video can be played with the MPEG (Moving Picture Experts Group)
decoder to decode movies.
 MPEG decoder can be either dedicated software or a special adapter card. One of
the MPEG decoder software is Power DVD by Cyber Link.
 It offers a wide variety of features such as DTS Digital Surround Decoder, Dolby
Pro Logic II and many others.

DVD-R
 DVD-Rs are recordable disks introduced in the end of 1997.
 Writing is possible only once but can be read so many times.
 Writing may also be referred to as Recording or Burning.
 The disk cannot be erased or re-written.
 There are two versions of DVD-R available.
 One is DVD-R for general use and DVD R(A) for authoring.
 DVD-R(A) is intended for professional development and is not rewritable.
 Both the types are readable in most DVD players and drives.
 The capacity of a first generation disk was 3.9 GB and later increased to 4.7 GB.
DVD-RW
 DVD-RWs are rewritable DVD disks introduced in the year 1999 that make it
possible to erase the previously recorded data and re-record again.
 Some of these disks can be erased and rewritten up to 1000 times.
 These disks have 4.7 GB capacity as a single layer DVD-ROM.
DVD-RAM
 These disks are introduced in 1998. Its initial capacity was 2.6 GB per side.
 Second generation DVD-RAM disks have the capacity of 4.7 GB per side and are
more suitable foe editing and accessing movies and music.
 Second generation disks are backward compatible with 2.6 GB DVD-RAM disks
and can read other DVD and CD formats.
4.6 PEN DRIVE
 It is a type of Universal Serial Cable (USB) flash drive.
 It is a kind of memory card that can be plugged into a computer’s USB port.
 It is termed “Pen drive” with reference to its size.
 It is small and compact thus making it fit into the palm of our hand.
 It is often flat and rectangular like a highlighter pen.
 A pen drive is used to store data and has a storage capacity of 64 MB to 32 GB.
 It is removable and rewritable.
It is mostly used as a backup for CDROMs or floppy disks.
4.6.1 Mechanism
 Pen drive consists of a small printed circuit board.
 This circuit board provides a strong base for the pen drive’s form and also serves
as a means to collect information.
 The circuit board consists of a small microchip within it.
 This microchip enables the pen drive to extract or feed in data.
 This process requires relatively low electrical power compared to CD-R’s or
Floppy.
 It is based on EEPROMS technology that allows writing and erasure process in a
computer system.
4.6.2 Transferring the data
 The data that is to be transferred is connected through a computer programme.
 It is then read, transmitted or rewritten from a pen drive to a computer or vice
versa.

 Thus the required data gets copied to any selected drive on the computer for
further use.
4.6.3 The working
 When a pen drive is connected to a USB port, it is activated.
 The USB port gives the pen drive access to the information on a specific
computer drive.
 Most of the pen drives are designed in such a way that they are compatible with
any USB port on a computer.
4.6.4 USB flash drive parts
1. USB connector
2. USB mass storage controller device
3. Test points
4. Flash memory chip
5. Crystal oscillator
6. LED
7. Write-protect switch (Optional)
8. Space for second flash memory chip
Internals of a typical flash drive
(Seitec brand USB1.1 pictured)
1 USB connector
2 USB mass storage controller device
3 Test points
4 Flash memory chip
5 Crystal oscillator
6 LED
7 Write-protect switch
8 Space for second flash memory chip

4.6.5 Components
 One end of the device is fitted with a single male type-A USB connector.
 In the printed circuit board, there are some simple power circuitry and small
number of ICs.
 Typically one of these ICs provides interface to USB port, another drives the
onboard memory & the other is the flash memory.
 The internal components of a typical flash drive are:
 USB connector: It is a cap that reduces the risk of damage due to static
electricity & improves overall drive appearance.
 USB mass storage controller device: This contains a small RISC
microprocessor and a small amount of on-chip ROM and RAM.
 Test points: This is used for testing during flash drive‘s manufacturing or
loading code into the microprocessor.
 Flash memory chip: It is a NAND flash memory chip that stores data. It is
typically also used in digital cameras.
 Crystal Oscillator: It produces the device‘s main 12MHz clock signal &
controls the device‘s data output through a phase-locked loop.
 LED: This indicates the data transfers or data reads & writes.
 Write-protect switch: This indicates whether device should be in ―write-
protection‖ mode.
 Unpopulated space for second flash memory chip: This provides space to
include a second memory chip that can be used for more than one storage
size device to meet needs of market.
4.6.6 Additional components
The typical device may also include:
 Jumpers and test pins - for testing during the flash drive's manufacturing or
loading code into the microprocessor.
 LEDs - indicate data transfers or data reads and writes.
 Write-protect switches - indicate whether the device should be in "write-
protection" mode.
 Unpopulated space - provides space to include a second memory chip. Having
this second space allows the manufacturer to develop only one printed circuit
board that can be used for more than one storage size device, to meet the needs
of the market.
 USB connector cover or cap - reduces the risk of damage due to static
electricity, and improves overall device appearance. Some flash drives do not
feature a cap, but instead have retractable USB connectors. Other flash drives
have a "swivel" cap that is permanently connected to the drive itself and
eliminates the chance of losing the cap.
 Transport aid - In some cases, the cap or main body contains a hole suitable for
connection to a key chain or lanyard or to otherwise aid transport and storage of
the USB flash device.
4.6.7 Advantages
 There are several advantages over other storage devices particularly the floppy
disk.
 They are faster, hold more data and are considered more reliable.

 They are impervious to scratches and dust that were problematic for previous
forms of portable storage.
 Durable solid state for transporting data from one location to another.
 The near ubiquity of USB support on modern PCs means that such a drive will
work in most places.
 The cheapest of Flash Drives will store dozens of floppy disks worth of data;
some hold more data than a CD; top Flash Drives can hold data more than a DVD.
 Most modern OS can read & write to flash drivers without any additional device
drivers.
4.6.8 Disadvantages
 They can sustain only a limited number of write & erase cycles before failure.
 Write operations will gradually slow as the device ages.
 They can be damaged or have data corrupted if an impact loosens circuit
connection.
4.6.9 Uses:
 Computer repair: They can be used as a mean to transfer recovery & antivirus
software to infected PCs and also a portion of machine data can be backed up in
case of emergency.
 System administration: They can be used to load configuration info and
software used for system maintenance, troubleshooting and recovery.
 Audio players: These are Flash drives with sound output and a simple user
interface. Examples: Apple Computer‘s iPod shuffle, Creative Labs MuVo.
 To boot OS: Flash drives can be used to launch any OS from a bootable flash
drive known as Live USB.
 In arcades: Flash drives can be used in arcade games to transfer high scores,
screenshots, dance edits & combos throughout sessions.
4.7 TAPE DRIVE
 A tape drive is a data storage device that reads and writes data on a magnetic
tape.
 Magnetic tape data storage is typically used for offline, archival data storage.
 Tape media generally has a favorable unit cost and a long archival stability.
 A tape drive provides sequential access storage, unlike a hard disk drive, which
provides random access storage.
 A disk drive can move to any position on the disk in a few milliseconds, but a
tape drive must physically wind tape between reels to read any one particular
piece of data.
 As a result, tape drives have very slow average seek times to data.
 Magnetic tape drives were first used for data storage on mainframe computers in
the 1950s, with capacities less than one megabyte.
4.7.1 Formats
Tape Drives come in various formats like:
 Digital Data Storage (DDS)
 Digital Linear Tape (DLT)
 Linear Tape Open (LTO)
 Advanced Intelligent Tape (AIT)
 Quarter Inch Cartridge (QIC) or Scalable Linear Recording (SLR)

4.7.2 Working
 A tape drive is a device that stores computer data on magnetic tape, especially
for backup and archiving purposes.
 Like an ordinary tape recorder, a tape drive records data on a loop of flexible
celluloid-like material that can be read and also erased.
 Tape drives work either by using a traditional helical scan where the recording
and playback heads touch the tape, or linear tape technology, where the heads
never actually touch the tape. Drives can be rewinding, where the device issues a
rewind command at the end of a session, or non-rewinding.
 Rewinding devices are most commonly used when a tape is to be unmounted at
the end of a session after batch processing of large amounts of data (payroll is
the classic example).
 Non-rewinding devices are useful for incremental backups and other
applications where new files are added to the end of the previous session's files.
4.7.3 Shoe-shining effect
 The shoe-shining effect occurs during a tape backup process when the transfer
rate of the data falls below the transfer speed of the tape drive.
 When this occurs, the data buffer of the tape drive empties and the drive must
stop, reverse position and begin writing once the tape buffer fills again.
 Shoe-shining can significantly affect the attainable backup speed and place
undue stress on the tape medium itself.
4.7.4 Advantages
A benefit of a tape drive backup is that tapes have a large capacity for storing
data and are very economical when compared to the cost of hard disk storage.
4.7.5 Disadvantages
A disadvantage is that tape drives store data sequentially, and the user can only
access specific data by starting at the beginning and rolling through the tape until the
desired data is located.

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