Transcript Understanding Computers, 10/e, Chapter 4

Chapter 3
Storage
Understanding Computers
1
Overview

This chapter covers:

Common characteristics of storage systems

Magnetic disk storage systems

Optical disc storage systems

Other types of storage, such as flash memory,
magnetic tape, remote storage, and smart cards
Understanding Computers
2
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).
Understanding Computers
3
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.
Understanding Computers
4
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.
Understanding Computers
5
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).
Understanding Computers
6
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.
Understanding Computers
7
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
Understanding Computers
9
Understanding Computers
10
Magnetic 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.
Understanding Computers
11
Magnetic 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.
Understanding Computers
12
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.
Understanding Computers
13
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.
Understanding Computers
15
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) .
Understanding Computers
16
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.
Understanding Computers
17
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). Understanding Computers
18
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.
Understanding Computers
19
Understanding Computers
20
Read-Only Discs: CD-ROM and DVDROM 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.
Understanding Computers
21
Recordable Discs:
CD-R, DVD+/-R

Recordable discs can be written to, but not erased or
rewritten.

Burning a CD or DVD permanently records data onto
the disc.

CD-R discs are commonly used to store data and for
custom music CDs.

DVD-R/DVD+R discs are commonly used for home
movies and other high-capacity applications.
Understanding Computers
22
Understanding Computers
23
Rewritable Discs:
CD-RW, DVD+/-RW

Rewritable discs can be used in the same way as
magnetic disks—data can be stored and erased as
needed.

Phase-change technology is used to record data onto the
disc using reflectivity.

Rewritable discs can be erased by reverting the reflectivity
back to the original state.

Blue laser discs are an emerging higher-capacity (23.3 GB)
form of optical disc.
Understanding Computers
24
Other Types of Storage Systems

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.
Understanding Computers
25
Understanding Computers
26
Other Types of Storage Systems, Cont’d

Flash memory media, cont’d.

Common forms of flash memory:



Flash memory sticks.
Flash memory cards—CompactFlash, Secure
Digital (SD), MiniSD, MultiMedia (MMC),
SmartMedia, and xD Picture cards.
Flash memory drives, such as USB flash drives.
Understanding Computers
27
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.
Understanding Computers
28
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.
Understanding Computers
29
Other Types of Storage Systems, Cont’d

Smart card: credit-card-sized piece of plastic that
contains some type of computer circuitry.

Holds less than a few megabytes.

Commonly used to store prepaid amounts of
digital cash or personal information.

Smart card readers are attached to a PC or built
into a cell phone, keyboard, or other device.
Understanding Computers
31
Other Types of Storage Systems, Cont’d

Holographic storage

Uses multiple laser beams to store data in three
dimensions.

Stores data in page format.

No moving parts and simultaneous access to all
data on a page.
Understanding Computers
33
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)
Understanding Computers
34
Summary

Properties of storage systems

Magnetic disk systems

Optical disc systems

Other types of storage systems

Comparing storage alternatives
Understanding Computers
35