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Understanding Computers C h.4 1 Chapter 4 Storage
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Understanding Computers Ch.41 Chapter 4 Storage. Understanding Computers Ch.42 Learning Objectives Explain the difference between storage systems and.

Mar 29, 2015

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Page 1: Understanding Computers Ch.41 Chapter 4 Storage. Understanding Computers Ch.42 Learning Objectives Explain the difference between storage systems and.

Understanding Computers Ch.4 1

Chapter 4

Storage

Page 2: Understanding Computers Ch.41 Chapter 4 Storage. Understanding Computers Ch.42 Learning Objectives Explain the difference between storage systems and.

Understanding Computers Ch.4 2

Learning Objectives

Explain the difference between storage systems and memory.

Name several general properties of storage systems.

Identify the two primary types of magnetic disk systems and describe how they work.

Discuss the various types of optical disc systems available and how they differ from each other and from magnetic systems.

Page 3: Understanding Computers Ch.41 Chapter 4 Storage. Understanding Computers Ch.42 Learning Objectives Explain the difference between storage systems and.

Understanding Computers Ch.4 3

Overview

This chapter covers:

Common characteristics of storage systems

Magnetic disk storage systems

Optical disc storage systems

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Understanding Computers Ch.4 4

Properties of Storage Systems: Storage Devices and Media

Involve two physical parts: a storage device and a storage medium.

Can be internal (located inside the system unit), or external (located outside the system unit).

Storage devices are identified by names and/or letters (e.g. “C” for first hard drive).

Page 5: Understanding Computers Ch.41 Chapter 4 Storage. Understanding Computers Ch.42 Learning Objectives Explain the difference between storage systems and.

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Properties of Storage Systems: Non-Volatility

Storage media are non-volatile:

When power to the device is shut off, data stored on the medium remains.

This is in contrast to most types of memory, which are volatile.

Page 6: Understanding Computers Ch.41 Chapter 4 Storage. Understanding Computers Ch.42 Learning Objectives Explain the difference between storage systems and.

Understanding Computers Ch.4 6

Properties of Storage Systems: Removable vs. Fixed Media

Fixed media: typically faster and less expensive.

Removable media: unlimited capacity and can be easily transported and secured.

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Understanding Computers Ch.4 7

Properties of Storage Systems: Random vs. Sequential Access

Random access ( direct access ): data can be retrieved in any order, independent of its physical location (most types of storage media).

Sequential access: data can be retrieved only in the same sequence in which it is physically stored (magnetic tape).

Page 8: Understanding Computers Ch.41 Chapter 4 Storage. Understanding Computers Ch.42 Learning Objectives Explain the difference between storage systems and.

Understanding Computers Ch.4 8

Properties of Storage Systems: Logical vs. Physical Representation

Logical file representation refers to the user’s view of the way data is stored (filename, folders, etc.).

Physical file representation is the actual physical way the data is stored on the storage media as viewed by the computer.

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Magnetic Disk Systems

Magnetic disks are the most widely used storage medium in computers today.

Data is stored by magnetizing particles on the storage medium.

Two common types: Floppy disks Hard disks

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Understanding Computers Ch.4 11

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Understanding Computers Ch.4 12

Floppy Disks and Drives

Floppy disk characteristics

Typically 3½ inches in diameter.

Typically hold 1.44 megabytes.

Inserted into floppy disk drive to be read from or written to.

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Floppy Disks and Drives, Cont’d. Disk is divided into tracks, sectors, and clusters.

The disk’s file directory keeps track of the contents of the disk so files can be retrieved (by filename) at a later time.

Page 15: Understanding Computers Ch.41 Chapter 4 Storage. Understanding Computers Ch.42 Learning Objectives Explain the difference between storage systems and.

Understanding Computers Ch.4 15

Floppy Disks and Drives, Cont’d.

Using floppy disks Must be inserted into the proper drive in the proper

direction. Should not be removed when the disk is being

accessed.

High-capacity removable magnetic disks and drives Zip disks (750 MB) SuperDisks (240 MB)

Page 16: Understanding Computers Ch.41 Chapter 4 Storage. Understanding Computers Ch.42 Learning Objectives Explain the difference between storage systems and.

Understanding Computers Ch.4 16

Hard Disk Drives Hard drive characteristics

Metal disk onto which data is stored magnetically.

Disks are usually permanently sealed inside the hard drive—allows faster speeds and storage of more data than removable systems.

Can be internal or external.

Page 17: Understanding Computers Ch.41 Chapter 4 Storage. Understanding Computers Ch.42 Learning Objectives Explain the difference between storage systems and.
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Understanding Computers Ch.4 18

Hard Disk Drives, Cont’d. Hard drive characteristics, cont’d

Organized into tracks, sections, clusters, and cylinders (the collection of tracks located in the same location on a set of hard disk surfaces).

Read/write head doesn’t touch the surface of the disk.

Bumping PC when disk is being accessed or dust or other obstacles on a hard-disk system can cause a head crash and damage the surface of the disk.

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Understanding Computers Ch.4 19

Hard Disk Drives, Cont’d. Disk access time.

Factors: seek time, rotational delay, data movement time

Can use multiple partitions.

Disk cache—strategy for speeding up system performance.

Hard drive standards (EIDE, SCSI, Fibre Channel, USB) .

Page 20: Understanding Computers Ch.41 Chapter 4 Storage. Understanding Computers Ch.42 Learning Objectives Explain the difference between storage systems and.

Understanding Computers Ch.4 20

Hard Disk Drives, Cont’d.

Portable hard drive systems

Offer large storage capacities and portability.

Either entire drive or just hard disk cartridge is transported.

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Understanding Computers Ch.4 21

Hard Disk Drives, Cont’d.

Storage systems for large computer systems and networks

Storage servers containing racks of hard drives.

Network attached storage (NAS).

Storage area networks (SANs).

RAID (for increased performance and/or fault tolerance).

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Understanding Computers Ch.4 22

Optical Disc Systems

Laser beams write and read data packed at very tight storage densities, many times finer than that of a typical magnetic disk.

Are typically 4½-inch discs, but can be a variety of shapes and sizes.

Data is stored optically on a continuous spiral track.

Can be CDs or DVDs.

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Read-Only Discs: CD-ROM and DVD-ROM Discs

CD-ROM discs cannot be written to or erased and typically hold 650 MB (e.g. music CDs).

DVD-ROM discs are similar to CD-ROM discs, but have higher capacity of 4.7 GB to 17 GB (e.g. movie DVDs).

Data is stored by burning pits into the disc surface that can be read using a laser beam.

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Other Types of Storage Systems, Cont’d

Flash memory media

Chip-based storage.

Solid state storage system—has no moving parts, so are more shock-proof and portable than conventional storage systems.

Commonly used with digital cameras, digital music players, handheld PCs, notebook computers, smart phones, etc.

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Other Types of Storages Systems, Cont’d

Magnetic tape systems—plastic tape that is magnetized to represent data.

Used primarily for backup and archival purposes (sequential access only).

Read from and written to via a tape drive.

Most tape media are in the form of cartridge tapes, though detachable-reel tapes exist as well.  

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Other Types of Storage Systems, Cont’d

Remote storage—storage devices that are not directly connected to your PC.

Network storage—accessible through a local network.

Online storage—accessible via the Internet and used for backup, as well as to transfer files to others.

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Comparing Storage Alternatives

Factors to consider: speed, expense, portability, storage capacity, and compatibility.

Most PC users require: Hard drive CD or DVD drive Floppy drive Additional devices (flash memory card reader,

etc.) as needed for the devices being used in conjunction with the PC (e.g. digital camera)

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Summary

Properties of storage systems

Magnetic disk systems

Optical disc systems

Other types of storage systems

Comparing storage alternatives