STORAGE DEVICES IntroductionComparisionStorage Hierarchy

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Hard Drive – storage RAM – memory

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.

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

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Why Is Storage Necessary?

Storage devices:Retain data when the computer is turned off

Are cheaper than memory

Play an important role during startup

Are needed for output

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Storage Devices

Storage devices are categorized by:The type of operations they perform

The method they use to access the information

The technology they use

Their location in the storage hierarchy

Their capacity and speed

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Sequential vs. Random Access Storage

Sequential – Storage devices that read and write data in a serial (one after the other) fashion

Random-Access – Storage devices that read and write data without going through a sequence of locations

Tape Drive – sequential storage

Hard Disk – random-access storage

Floppy Disk Drive – random-access storage

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Storage Technologies: Magnetic and Optical

Magnetic – Storage devices use disks or tapes that are coated with magnetically sensitive material

Optical – Storage devices that use laser beams to read patterns etched into plastic disks

Magnetic Storage Optical Storage – CD/DVD drive

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The Storage HierarchyThe three levels of storage hierarchy 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

Storage Capacity and Speed

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

the device to begin reading data

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Platter Read/Write head

Hard Disks

Hard disks are 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.

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

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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).

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Floppy and Zip Disks and Drives

A disk or diskette is a portable storage medium. High-density floppy disks that are commonly

used today store 1.44 MB of data. Disks work with a disk drive. Zip disks store up to 750 MB of data and are not

downwardly compatible with floppy disks.

Zip DriveFloppy DriveClick on the picture to see it work.

Floppy Disk

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CD-ROM Discs and Drives

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

CD-ROM drives can not write data to discs.

They are capable of storing 650 MB of data.

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

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CD-R and CD-RW Discs and Recorders

CD-R Discs can be read and

written to Discs can only be

written to “once” CD-R drives are capable

of reading and writing data

CD-RW Discs can be read and

written to Discs are erasable Discs can be written to

many times CD-RW drives are

capable of reading, writing, and erasing data

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DVD-ROM Discs and Drives

DVD stands for Digital Video Disc. DVD technology is similar to CD-

ROM technology. DVDs are capable of storing up to

17GB of data. The data transfer rate of DVD drives is

comparable to that of hard disk drives. DVD-R and DVD-RW drives have the

ability to read/write data.

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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.

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Compact Flash Memory

Flash Memory

Smart Card

Micro Drive

Memory Stick

PC Card

Solid State Storage Devices

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Chapter 5 Summary• Input is the software, data, and information that is entered into

the computer’s memory.• Input devices such as the keyboard, mouse, and trackball enable

the user to enter data.• A pointing device enables the user to control movements of an

on-screen pointer. • Speech recognition software enables the user to enter data into

a computer by speaking into a microphone.• Video and images can be entered into a computer by way of

digital cameras, scanners, and fax modems. • Monitors enable the user to view the computer’s processed

data. The output is known as soft copy.

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Chapter 5 Summary (continued)• The two types of monitors are the CRT and the LCD.• A monitor’s quality is measured by screen size, resolution, and

refresh rate.• Printers produce permanent versions (hard copies) of the

computer’s output.• The two basic types of printers are the inkjet and laser.• Memory makes software and data available for the CPU’s use.• Storage devices are categorized by:

Data access (sequential or random-access)Technology (magnetic, optical, or solid state)Hierarchy (online, near-online, or offline)Operations (read-only or read/write)

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Chapter 5 Summary (continued)

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

• Optical storage devices include:CD-ROM– Read-onlyCD-R– Record onceCD-RW– Erasable, write repeatedlyDVD-ROM– Read-onlyDVD-R– Read/write

• Solid state storage devices include:PC cardsFlash memory cardsSmart cards

Thanks....................

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