Transcript Chapter 6: Storage - Mesa Community College

Secondary Storage
CIS 105
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Topics
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List the benefits of secondary
storage.
Identify and describe storage
media that are available for
personal computers.
Describe how data is stored
on a disk.
Lists the items that effect a
hard drive’s access time.
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Information Processing Cycle
Input
Raw Data
Process
(Application)
Output from one process can
serve as input to another process.
Output
Information
Storage
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Secondary Storage
Secondary storage is used to store programs
and data that are not currently being used.
 Examples:
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Hard drive, USB Flash Drives , CD, DVD
When programs and data are needed, they
must be retrieved from the storage device
and loaded into RAM (primary storage).
 The CPU only executes commands and
manipulates data loaded in RAM.
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Memory (RAM) vs. Storage
(Volatile)
Temporarily holds program
instructions to be executed and
data that is currently being
manipulated.
(Non-volatile)
Holds data, instructions,
and information that can
be retrieved and loaded
into RAM when needed.
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Benefits of Secondary Storage

Benefits
Space
 Reliability
 Convenience
 Economy

Programs and data can be saved and
retrieved when needed.
 Referred to as Reading and Writing.
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Multi-platter Drives
Hard Drives
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Hard Disk Characteristics
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Read and Write heads are used to store and retrieve data.
Read and Write heads do NOT touch the platters, if they
do, it is called a Head Crash.
Data is stored magnetically.
Access arms are used to
position the heads.
Multi-Platter - both sides of
platter are recordable.
Very large capacity.
Removable and External
hard drives are now available,
and are great for backups.
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Format Commands
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Low Level Format – software provided by vendor.
High Level Format – performed by operating system.
Formatting is the process of preparing a storage device for
reading or writing.
 Formatting erases all data on.
 Partitions can be created during formatting, and a
partition is a logical division of a hard disk created so
that you can have different operating systems on the
same hard disk or to create the appearance of having
separate hard drives for file management, multiple
users, or other purposes.
 Format defines Tracks, Sectors, Cylinders, and File
Allocation Table (FAT) – this items are defined in the next few slides.9
Tracks and Sectors
Formatting organizes the disk into storage
locations called tracks ( a band that forms
a circle on the disk).
Formatting breaks the tracks into sectors
which are small pie-shaped areas.
Data processed one or more sectors at a time
called clusters.
In a multi-platter hard disk, the same track on
multiple platters together form a cylinder
(next slide).
Tracks
Sectors
(Cluster: 1-8 sectors)
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Cylinders
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In a multi-platter hard
disk, the same track on
multiple platters together
form a cylinder.
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MZR
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With normal sectors,
there is a lot of wasted
space on the sectors
located on the outer
tracks.
Multiple Zone
Recording (MZR) –
data is recorded at the
same density on all
tracks so that outer
tracks have more data.
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File Allocation Table (FAT)
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FAT – list of clusters and used to keep track of where files
are on the disk.
FAT includes Filename, File size, and the cluster
number of where a file begins and additional
directory info
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When a file is deleted, the data on the disk is still there,
only the entry in the FAT is marked as deleted so another
file can eventually be saved in it’s location.
That is why data can still be recovered after you think it
has been deleted.
NTFS – Windows New Technology File System is more
secured then FAT and uses MFT (Master File Table) to
track where files are stored.
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FAT and MFT are stored on the actual storage device.
Access Time

Access Time - the time required to locate data on
the storage device – 3 things affect access time.
 Seek Time – the time it takes the access arm
with the read/write heads to get into position
over the track.
 Head Switching – the activation of a particular
read/write head.
 Rotational Delay (latency) – the time it takes
for the sector containing the data to rotate under
the read/write head.
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Data Transfer Rate
Data Transfer Rate – the time it takes to
transfer the data to and from the disk to
RAM.
 While the computer is running, the platters
spin at a constant high speed, 5400-15000
revolutions per minute (rpm).
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Hard Disk Controller
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Hard disk controller transfers
data between the hard disk
and the system bus.
The controller may be part of
the hard disk, motherboard,
or a separate expansion card.
Common Interfaces:
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SATA – Serial Advanced Technology Attachment
Some external drives can use this interface (eSATA)
transfer rate: 1.5 or 3.0 gigabits per second (Gbit/s)
EIDE – Enhanced Integrated Drive Electronics (parallel)
Also know as ATA and PATA
transfer rate of last version ATA-7: 133 Mbits
USB 2.0 transfer rate: 480 Mbits per second (use eSATA)
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Fragmented Disk
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Fragmented disk occurs when files are stored in
non-contiguous clusters
How does fragmentation affect access time?
http://www.diskeeper.com/
Perfect Disk – www.raxco.com
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Windows Disk Defragmenter
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RAID (Redundant Array of Independent Disks)
There are about 9 levels
Level 1 - Data is duplicated – auto backup and fault tolerant –
disk mirroring with no striping
(RAID LEVEL 0)
Level 0 - File saved across different drives
called striping.
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Optical Storage Technology
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Compact Discs (CD)
CD-ROM – Read Only Memory
 CD-R – Recordable – Write Once
 CD-RW – ReWritable
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Digital Versatile Discs (DVD)
DVD – Read Only
 DVD-R, DVR+R – Recordable – Write Once
 DVD-RAM, DVD-RW, DVD-+RW – ReWritable
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Compact Disc Drives
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CD-ROM - drive can only read data
from CDs
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CD-R - drive can write to disk once
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CD-ROM stores up to 650 MB per disk
Disk can be read by CD-ROM or CD-R
drive
CD-RW - drive can erase and record
data multiple times on RW media
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Some compatibility problems trying to read
CD-RW disks on CD-ROM drives
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Digital Versatile Disk (DVD)
Short wavelength laser can read densely
packed spots
 DVD drive can read CD-ROMs
 Capacity from 4.7GB (Single Layer-Single
side) up to 27GB (Dual Layer-Double Side)
 Data store tighter on higher capacity discs.
 Allows for full-length movies
 High-Density DVD (HD-DVD) 15 - 60GB
 Blu-ray discs – 25 – 100GB
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(2007 became industry standard)
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DVD-Dual Layer
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(pcworld 4/2005)
Two layers, one disc: This side view shows the two dyerecording layers of a double-layer DVD. When the laser writes
to the disc, it directs its beam to either layer one or layer two.23
Magnetic Tape Storage
Plastic tape with a magnetic coating.
 Primarily used in large organizations.
 There are small tape drives for small businesses
and home use, but not too common.
 Need a tape drive
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Erase head
 Read/Write head
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Used for backups.
 Sequential access
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Flash Memory Cards
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A flash memory card
is a removable storage
device.
Consists of circuits
with NO moving parts.
Used by PDAs, phones,
digital cameras, some
MP3 players.
Includes USB Flash Drives.
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Backup System
Need to backup data on storage devices.
 Copies should be saved onsite and offsite.
 Why?
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Hard drives may fail (head crash)
 Fire
 Natural disasters
 Thief
 Vandalism
 Government requirements
 To save your job
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Summary




List the benefits of secondary storage.
Identify and describe storage media that
are available for personal computers.
Describe how data is stored on a disk.
Lists the items that effect a hard drive’s
access time.
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