ptaff_6_chp4

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Chapter 4

Storing Data: Electronic Filing Cabinets

COMPUTERS IN YOUR FUTURE 2004COMPUTERS IN YOUR FUTURE 2004by Bryan Pfaffenberger and Bill Daley

Differences between memory and storage How storage media are categorized How a storage device’s performance is measured How data is stored on hard and floppy disks Characteristics of hard drives Uses of removable disks Types of optical storage media New types of storage media

Chapter 4

Storing Data: Electronic Filing CabinetsWhat You Will Learn

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Hard Drive RAM Memory

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Memory vs. Storage

Storage, also known as mass media or auxiliary storage, refers to the various media on which a computer system can store data.

Storage devices hold programs and data in units called files.

Files are stored in directories or folders.

Memory is a temporary workplace where the computer transfers the contents of a file while it is being used.

Copyright © 2003 Prentice Hall, Inc 6NEXT SLIDE

Why is storage necessary?

Storage:

Retains data when the computer is turned off.

Is cheaper than memory.

Plays an important role during startup.

Plays an input role when starting applications.

Is needed for output.

Devices can hold a large amount of data.


Storage Devices

Storage devices are:

Hardware that is capable of retaining data when the electricity is turned off.

Able to read (retrieve) data from a storage medium (disk/tape).

Able to write (record) data to a storage medium.


Types of Storage Technologies

Sequential– Hardware that reads and writes data in a serial (one after the other) fashion.

Random-Access– Hardware that reads and writes data without going through a sequence of locations.

Magnetic– Hardware that uses disks or tapes that are coated with magnetic material.

Optical– Hardware that uses laser beams to read data from plastic disks.

Solid State– Devices that use nonvolatile memory chips to read and write data.

Tape Backup Unit

Floppy Drive Hard Drive Jaz Drive Zip Drive

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Sequential – Magnetic Storage

Random-Access – Magnetic Storage

CD-ROM / DVD Drive

Magneto-Optic (MO) Drive

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Sequential – Optical Storage

Magnetic – Optical Storage


CompactFlash MemoryFlash Memory

Smart Card

Micro Drive

Memory

Stick

PC Card

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Solid State Storage


The Storage Hierarchy

Storage hierarchy consists of three levels. They are: Online storage– Also called primary storage, it is

made up of the storage devices that are actively available to the computer system. User action is not required.

Near-online storage– Also called secondary storage, it is not readily available to the computer system. The user performs an action, such as inserting a disk, to make it available.

Offline storage– Also called tertiary storage or archival storage, it is not readily available to the computer system. Devices such as tape backup units store data for archival purposes.

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Floppy Disk Hard Drive CD ROM / DVD

Capacity– 720 KB to 1.44 MB

Access Time– 100ms

Capacity– Up to 80 GB

Access Time– 6 to 12ms

Capacity– CD-ROM 650 MB; DVD 17 GB

Access Time– 80 to 800ms

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Capacity and Speed of Storage Devices

A storage device’s performance is measured by:

Capacity– The number of bytes of data that a device can hold.

Access Time– The amount of time, in milliseconds (ms), it takes for the device to begin reading data.


Disks and Disk Drives

A disk or diskette is a portable storage medium. Disks are circular plastic disks coated with a

magnetically sensitive film. Disks work with a disk drive. High-density floppy disks are commonly used today.

Floppy disks store 1.44 MB of data.

SuperDisk and High FD disks store up to 250 MB of data and are downwardly compatible with floppy disks.

Zip disks store up to 750 MB of data and are not downwardly compatible with floppy disks.

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Protecting Your Data on Disks


Click on picture to view video

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How Disk Drives Work

Once inserted, the floppy disk spins on a spindle.

The head actuator moves the read/write head over the surface of the disk to the location of the data to be read.

Data is read into computer’s memory.


Track

Sector

Cluster

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Disk Organization

A disk is formatted–that is, it is divided into tracks and sectors and a file allocation table (FAT) is created. Track– circular band Sector– pie shaped section Cluster– two or more adjacent sectors FAT– keeps track of specific locations of files


Platter Read/Write head

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How Hard Disks Work

Hard disks are a high-speed, high-capacity storage devices.

They contain metal disks called platters.

They contain two or more stacked platters with read/write heads for each side.

They work similarly to floppy disk drives.

Hard disks can be divided into partitions to enable computers to work with more than one operating system.


Factors Affecting a Hard Disk’s Performance

Seek time or positioning performance– How quickly the read/write head positions itself and begins transferring information. It is measured in milliseconds (ms).

Spindle speed or transfer performance– How quickly the drive transfers data. It is measured in rotations per minute (RPM).

Latency– The time it takes for the spinning platter to bring the desired data to the read/write head. It is measured in milliseconds (ms).


Hard Disk Interfaces

A hard disk controller provides an interface which enables the hard disk to communicate with the CPU.

Types of interfaces:

Integrated Drive Electronics (IDE), also called ATA or IDE/ATA

Ultra DMA/66

Ultra DMA/100

Small Computer System Interface (SCSI)


Jaz Drive

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Removable Hard Disks

Removable hard disks contain platters that are enclosed in a cartridge which can be inserted or removed from a drive.

They are used for data archiving and data backup.


Tape Backup Unit

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Magnetic Tape

Magnetic tape backup units store large amounts of data that are not used frequently.

They use a cassette-type reel-to-reel plastic tape.


CD-ROM Disks and Drives

CD-ROM stands for Compact Disk-Read Only Memory.

CD-ROM drives can not write data to disks.

They are capable of storing 650 MB of data.

They are used for storing operating systems, large application programs, and multimedia programs.


CD-R and CD-RW Disks and Recorders

CD-R

Disks that can be read and written to.

Disks can only be written to “once”.

Drives that are capable of reading and writing data are needed.

CD-RW

Disks that can be read and written to.

Disks are erasable.

Disks can be written to many times.

Drives that are capable of reading, writing and erasing data are needed.


DVD-ROM Disks and Drives

DVD stands for Digital Video Disk.

They use technology similar to CD-ROM.

They are capable of storing up to 17GB of data.

Their data transfer rate is comparable to that of hard disk drives.

They are compatible with CD-ROM disks.

DVD-RAM– Has the ability to read/write data.


Other Optical Storage Technologies

Write Once, Read Many (WORM) systems use 12-inch optical disks that store up to 15 GB.

Magneto-Optical (MO) disks are erasable and they combine magnetic principles with optical technology.

Magnet-Optical Drive

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Storage Horizons

Florescent multilayer disc-read-only memory (FMD-ROM) uses optical technology to create disks with up to 100 layers of data. Laser beams strike the disc’s fluorescent layers. Up to 1 terabyte (TB) of data can be stored on

each disc.

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Solid State Storage Devices

Solid state storage devices use nonvolatile memory chips to retain data.

They do not have moving parts.

They are small, lightweight, reliable, and portable.


PC Cards

PC or PCMCIA card– Credit card-sized device used mainly with notebook computers.

Their various functions include:

Modems

Network adapters

Additional memory or storage


CompactFlash Memory StickSmartMedia

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Flash Memory Cards

Flash memory card– A wafer-thin card used with cellular phones, MP3 players, and digital cameras.

Types of flash memory cards:

SmartMedia card

CompactFlash card

Sony’s Memory Stick


Smart Cards

Smart card– Credit card-sized device combining flash memory with a microprocessor.

It is used as a credit card.

They offer more functionality, greater convenience, and higher safety than credit cards.


Enterprise Storage Systems

Enterprise storage systems are developed by corporations to cope with their information storage needs.

They use several storage technologies: Tape libraries Hard disks Optical disc libraries Tape backup systems

A new technology being developed is the Storage area network– Links high-capacity storage devices to all of the organizations servers.

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Chapter 4 Summary

1. Memory makes software and data available for the CPU’s use.

2. RAM is volatile.

3. Storage devices are nonvolatile.

4. Storage devices are categorized by:A. Operations (read-only or read/write)B. Data access (sequential or random-access)C. Technology (magnetic, optical, or solid state)D. Hierarchy (online, near-online, or offline)

5. Disk organization includes:A. TracksB. SectorsC. ClustersD. File allocation tables

1. Memory makes software and data available for the CPU’s use.

2. RAM is volatile.

3. Storage devices are nonvolatile.

4. Storage devices are categorized by:A. Operations (read-only or read/write)B. Data access (sequential or random-access)C. Technology (magnetic, optical, or solid state)D. Hierarchy (online, near-online, or offline)

5. Disk organization includes:A. TracksB. SectorsC. ClustersD. File allocation tables


Chapter 4 Summary cont.

6. Hard disks store more data than other storage devices.

7. A hard disk’s performance is measured by its positioning performance and transfer rate.

8. IDE and SCSI are two hard drive interfaces.

9. Optical storage devices include:A. CD-ROM– Read-onlyB. CD-R– Record onceC. CD-RW– Erasable, write repeatedlyD. DVD-ROM– Read-onlyE. DVD-RAM– Read/write

6. Hard disks store more data than other storage devices.

7. A hard disk’s performance is measured by its positioning performance and transfer rate.

8. IDE and SCSI are two hard drive interfaces.

9. Optical storage devices include:A. CD-ROM– Read-onlyB. CD-R– Record onceC. CD-RW– Erasable, write repeatedlyD. DVD-ROM– Read-onlyE. DVD-RAM– Read/write


10. Solid state storage devices include:

A. PC cards

B. Flash memory cards

C. Smart cards

11. Corporations develop enterprise storage systems for their information storage needs.

10. Solid state storage devices include:

A. PC cards

B. Flash memory cards

C. Smart cards

11. Corporations develop enterprise storage systems for their information storage needs.

Chapter 4 Summary cont.

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THE

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