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STORAGE DEVICES

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IIUI

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Stored-Program Concept

The von Neumann architecture

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Memory

■Memory is a collection of cells, each with a unique physical address

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Memory Hierarchy

Slow and inexpensive

Increasing performance and

increasing cost

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Storage Devices■ Storage device stores information to be

recalled and used at a later time■ Storage device consists of:

■Storage medium■Storage device

■ Three major technology types for information storage:

■Magnetic■Optical or laser■Flash memory

                     

          

SimNet Concepts Support CD: “Storage Concepts”

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Storage Medium Terms– Bit– Byte– Kilobyte (KB)– Megabytes

(MB)– Gigabytes

(GB)– Terabytes

(TB)– Petabyte (PB)– Exabyte (EB)– Zettabyte– Yottabyte

Smallest Unit of Memory

= 8 bits≈ 1024 Bytes≈ 1024 K- Bytes≈ 1024 M-Bytes≈ 1024 G-Bytes≈ 1024 T-Bytes≈ 1024 P-Bytes≈ 1024 E-Bytes≈ 1024 Z-Bytes

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Bits and bytes■A computer only understands the

numbers 0 or 1, or whether a switch is on or off.

■We call those 1s and 0s ‘bits’ – binary digits

■A byte (made up of 8 bits) is enough computer memory to store a single character of data (e.g. the letter F).

■The computer uses a code to understand what each bit pattern means.

■Using the ASCII code, for instance, the letter F is 70 and has a bit pattern of 01000110.

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Magnetic and Optical Storage

Storage Media

Magnetic Storage

Media Sealed Inside Drive

Internal Hard Drive

External hard Drive

Removeable

Storage Media

Floppy Disk Zip Disk

Optical Storage Media

CD

CD-ROM CD RW CD R

DVD

DVD ROM DVD RW

Blue Ray Disk

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Levels of Storage Hierarchy

Levels

Online Storage

Near-Online

StorageOffline Storgae

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Magnetic Storage Media■ Magnetic storage devices can

be either internal or external• Internal magnetic hard

disks are fixed inside the system unit

• External magnetic hard disks are portable

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Magnetic Disks■ A read/write head travels across a spinning magnetic disk,

retrieving or recording data

The organization of a magnetic disk

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Internal Magnetic Hard Disk■Internal hard disk is a magnetic storage device

with • One or more thin platters that store

information sealed inside the disk drive.• Read/write heads access the information on

surface• Heads read information while copying it

from disk to RAM• Heads write information when copying it

from RAM to disk■Long term storage system and application

software■Operating system and application software are

copied from the hard disk to memory■Capacity measured in gigabytes

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Hard Disk■The hard drive is the main and usually largest

data storage device in computer.■It can store anywhere from 160 GB to 2TB.■Hard disk speed is the speed at which content can

be read and written on a hard disk.■A hard disk unit comes with a set rotation speed

varying from 4500 to 7200 rpm.■Disk access time is measured in milliseconds.

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Disk Storage

Head AssemblyAll heads move

together Platter

Sector

Top and bottom Surfaces

Head Spindle Track

Shaft Arm

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Disk Storage

Cylinder X: Track X

from all 12 surfaces

(2 per platter)

Each circle represents

two tracks: one for top surface

and one for bottom surface

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Disk Storage

(a) Normal (Non zoned) recording (b) Zoned recording

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External Magnetic Hard Disk■External hard disks are

magnetic storage media which are portable storage units that you can connect to your computer as necessary• Great for backup storage

devices• Ability to transport your

hard disk from one computer to another

                     

          

                     

          

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Comparison

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Magnetic Tape

■The first truly mass auxiliary storage device was the magnetic tape drive

A magnetic tape

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Types of backing storageThe medium is what the data is actually stored on. Examples of media include floppy disks, CD-ROMs and zip disks.

Floppy disks hold about1.44 MB of data.

Zip disks store up to750 MB of data.

CDs hold around 700 MB of data.

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Removable Magnetic Storage: Floppy Disk

■Floppy Mylar disk– Housed inside a hard

plastic casing– Thin, flexible plastic

disk■ 3.5 inch floppy disks

– also called floppies, diskettes, floppy disks

– Holds about 1.44 megabytes of information

■ High-capacity disks– Zip® disk

p. 5.144 Fig. 5.15

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Floppy Disk

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Removable Magnetic Storage: Zip Disk

■High capacity plastic platter disk– Called removable hard disks– Provide a higher storage capacity than

Mylar disks■Example - Zip® disk with capacity of 100MB,

250MB, and 750MB

                     

          

                     

          

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Optical Storage Media■Read-Only

CD-ROM DVD-ROM

■One-Time Writable CD-R DVD-R DVD+R

■Fully Read-and-Write CD-RW DVD-RW or

DVD+RW or DVD-RAM

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Optical Storage■ CDs■ DVDs■ Both are optical storage and

have three formats:– Read-only– Write-once– Read-and-write

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Comparison

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Flash Memory Cards

■Flash memory cards have high-capacity storage laminated inside a small piece of plastic

■Flash flash memory cards do not need a drive with moving parts to operate

                     

          

                     

          

                     

          

                     

          

                     

                   

                     

          

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Zip Disk Drive

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USB Flash Drive

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Latest Technologies

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Data is stored using binary code (0 and 1).Computer memory is measured in kilobytes.Read Only Memory (ROM) is non-volatile because it cannot be changed.Random Access Memory (RAM) is volatile because it only works when the computer is switched on.There are three types of storage device: those that use magnetic media, others that use optical media, and those that use flash memory.Different types of media have different storage capacities.Storage devices can also be divided into those that are fixed and those that are removable.

Summary