1

Storing

And

Retrieving Information

2

Mass Storage and Files• Programs and information

(text, image, audio, video) are stored:

– Magnetic • Magnetic Tape• Magnetic Disk• USB

– Optical• DVD• CD-ROM• CD-R• CD-RW

•Other•USB FLASH•MO•Solid State Drives

Computer Files

4

Hard Disks

• Faster and more storage than diskettes

• Anatomy:– Recording surface– Multiple platters– Read/write head– Access arms

Courtesy of Seagate Technology

5

Fixed Hard Disk

6

Backing Up Files

• Magnetic Tape used for:– Backup or protection– Archiving

• Tape backup units (TBUs)• USB 2.0• USB Portable Hard Drives

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Backing Up Files

• Backup methods:– Full– Selective– Modified files only

• Other backup options:– Server computer– Notebook/desktop PC– CD-R or CD-RW– Interchangeable external hard disk

Magnetic Disks

Sequential-accessas well

Random or Direct Access

Hard/Fixed DisksPermanently installed and cannot be removed

- Data stored on all recording surfaces. - Allows greater density than interchangeable diskettes

Interchangeable Disks

Can be stored offline and loaded to the magnetic disk drives as they are needed

- Floppy Disk, Super Disks, or Zip Disks- Interchangeable Hard Disks

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Case & Inside

10

• Formatting is considered HARD DRIVE preparation.

– Initialize disk with recording format for your operating system.

• Low-Level Formatting - Creates sectors and tracks on disk into which data are stored.

• High Level Formatting - Sets up VFAT, Master Boot Record is created, copies hidden operating system files to the volume, and prompts you for a label i.e. MY Computer.

http://www.ranger.cc.tx.us/COSC_training/xstudy5.htm

• ScanDisk for lost clusters– Sooner or later your PC will give a “lost clusters found” message,

indicating that the hard disk has orphan clusters that don’t belong to a file. Typically, lost clusters are the result of an unexpected interruption of file activity, perhaps a system crash or loss of power. Windows users should run the ScanDisk utility program periodically to “scan” the disk for lost clusters and, if any are found, let you return them to the available pool of usable clusters.

• Defragmentation

Head Crash

Magnetic Disk Organization

• Disk Address– Tracks/Sectors/

• Clusters– Cylinders

• Write data – Magnetize disk’s thin

coated surface

• Read data– Sense absence or

presence of a bit

• Magnetic Disks spin At Constant Angular Velocity

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Magnetic Disk Organization

• VFAT: Virtual File Allocation Table

– ScanDisk for lost clusters

• Defragmentation

– Re-Ordering Files Back into Continuos Clusters

• Formatting

• Disk Speed

– Access time

– Data transfer rate

– Disk caching

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File 1st Cluster

Expenses.xls 1

Annual Rep.doc 2

AVAILABLE 3

NewBudget.mdb

4

Cluster Track Sectors

3 1 2,3,4,5

VFAT: Writing a file

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VFAT: request for a particular file.

1. The operating system searches the VFAT to find the physical address of the first cluster of the file.

2. The read/write heads are moved over the track/cylinder containing the first cluster.

3. The rapidly rotating disk passes the cluster under/over the read/write head and the information in the first cluster is read and transmitted to RAM for processing.

4. The operating system checks an entry within the initial cluster that indicates whether the file consists of further clusters, and if so, where on the disk they are located.

5. The operating system directs that clusters continue to be read and their information transmitted to RAM until the last cluster in the chain is read (no further chaining is indicated).

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DEFRAGGING YOUR HARD DRIVE

Optical Disks

Spiraling Track

Detector

Pit

Land

Sector

Less sensitive to environment

Cheaper than magnetic disks

Large data capacity

Spins at Constant Linear

Velocity

Optical Disks: Write-Only

• CD-ROM– Compact Disk: read only memory– Cannot be altered– Speeds: 32X, 40X or 75X (spin rate)– Capacity: 700 MB *

• DVD-ROM– Capacity: 4.7 GB to 17 GB– Backward compatible with CD-ROM

Optical Disks: Read/Write

• CD-R– Compact disk-

recordable

• CD-RW– Compact disk-

rewritable – Will not work with

older CD-ROM drives

• DVD-R• DVD-RW• DVD-RAM

– Rewritable

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CD surface area

Inside the CD Player and Reading from a CD

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DVDs (Digital Video Disc or Digital Versatile Disk) sides