-
CHAPTER
8
SECONDARY
STORAGE
P213
Introduction
Secondary
storage
devices
are
used
to
save,
to
back
up,
and
even
to
tran
sport
files
consisting
of
data
or
programs
from
one
location
or
computer
to
another.
Not
long
ago,
almost
all
files
contained
only
numbers
and
lett
ers.
The
demands
for
saving
these
files
were
easily
met
with
low-
capacity
floppy
disk
drives
and
hard-disk
drives.
Data
storage
has
expanded
from
text
and
numeric
files
to
include
digita
l
music
files,
photographic
files,
video
files,
and
much
more.
These
new
ty
pes
of
files
require
secondary
storage
devices
that
have
much
greater
cap
acity.
Secondary
storage
devices
have
always
been
an
indispensable
element
i
n
any
computer
system.
They
have
similarities
to
output
and
input
device
s.
Like
output
devices,
secondary
storage
devices
receive
information
from
the
system
unit
in
the
form
of
the
machine
language
of
0s
and
Is.
Rathe
r
than
translating
the
information,
however,
secondary
storage
devices
sav
e
the
information
in
machine
language
for
later
use.
Like
input
devices,
s
econdary
storage
devices
send
information
to
the
system
unit
for
processi
ng.
However,
the
information,
since
it
is
already
in
machine
form,
does
n
ot
need
to
be
translated.
It
is
sent
directly
to
memory
(RAM),
where
it
c
an
be
accessed
and
processed
by
the
CPU.
Competent
end
users
need
to
be
aware
of
the
different
types
of
second
ary
storage.
They
need
to
know
the
capabilities,
limitations,
and
uses
of
fl
oppy
disks,
hard
disks,
optical
discs,
and
other
types
of
secondary
storage.
Additionally,
they
need
to
be
aware
of
specialty
storage
devices
for
porta
ble
computers
and
to
be
knowledgeable
about
how
large
organizations
ma
nage
their
extensive
data
resources.
辅助存储设
备被用来保存，
备份，
甚至把数据或程序从一个位置或计算机传
送到另一个地方。
前不久，
几乎所有的
文件只包含数字和字母。
保存这些文件的
要求很容易满足，只需
要低容量的软盘驱动器和硬盘驱动器。
数据存储已经从文字
和数字文件不断扩大，包括数字音乐文件，照相文件，
视频文件，以及更多。这些新类型
的文件需要有更大容量的辅助存储设备。
辅助存储设备一直是
在任何计算机系统中不可缺少的元素。
他们在输出和输
入设备有
相似之处。像输出设备一样，辅助存储设备从系统单元接收的信息是
0
和
1
的机器语言的形式。然而，辅助存储设备上用机器语言保存信息是为了
供以后使用，
而不是转换信息。
像输入设备一样，
辅助存
储设备将信息发送到系
统的单元进行处理。
然而，
这些信息，
因为它们已经是机器的形式，
并不需要转
换。它们直接发送到内存（
RAM
），
在那里它们可以被
CPU
直接访问和处理。
有能力的终端用
户需要认识不同类型的辅助存储器。
他们需要了解软盘、
硬
盘、
光盘和辅助存储器的其他类型的容量、
限制和使用。此外，
他们还需要了解
便携式计算机的专业存储设
备和大型组织如何管理其广泛的数据资源的知识。
P214
STORAGE
An
essential
feature
of
every
computer
is
the
ability
to
save,
or
store,
i
nformation.
As
discussed
in
Chapter
6,
random-access
memory
(RAM)
hold
s
or
stores
data
and
programs
that
the
CPU
is
presently
processing.
Befor
e
data
can
be
processed
or
a
program
can
be
run,
it
must
be
in
RAM.
Fo
r
this
reason,
RAM
is
sometimes
referred
to
as
primary
storage.
Unfortunately,
most
RAM
provides
only
temporary
or
volatile
storage.
T
hat
is,
it
loses
all
of
its
contents
as
soon
as
the
computer
is
turned
off.
I
ts
contents
also
are
lost
if
there
is
a
power
failure
that
disrupts
the
elect
ric
current
going
into
the
system
unit.
This
volatility
results
in
a
need
for
more
permanent
or
nonvolatile
storage
for
data
and
programs.
We
also
need
external
storage
because
users
need
external
more
storage
capacity
t
han
is
typically
available
in
a
computer
’
s
primary
of
RAM
memory.
每一台计算机的一个重要功能是保存或储存信息的能力。像在第
6
章讨论
的，随机存取
存储器（
RAM
）持有或存储
CPU
现在处理的数据和程序。在数据
可以被处理或程
序可以运行之前，它们必须在
RAM
中。出于这个原因，
RAM
有
时也被称为主存储器。
不幸的是，
大多数
RAM
仅提供临时或易失性存储。
也就是说，
一旦关闭计算
机后它就失去它的所有内容。
如果有电源故障中断系统单元的供电，
其内容也丢
失。
这种波动的结果需要更多的
永久或非易失性存储数据和程序。
我们还需要外
部存储，因为用
户需要更多的外部存储容量
,
比通常在计算机
< br>RAM
主内存中可用
的多。
Secondary
storage
provides
permanent
or
nonvolatile
storage.
Using
seco
ndary
storage
devices
such
as
a
floppy
disk
drive,
data
and
programs
can
secondary
be
retained
after
the
computer
has
been
shut
off.
This
is
acco
mplished
by
writing
files
to
and
reading
files
from
secondary
storage
devi
ces.
Writing
is
the
process
of
saving
information
to
the
secondary
storage
device.
Reading
is
the
process
of
accessing
information
from
secondary
st
orage.
This
chapter
focuses
on
secondary
storage
devices.
Some
important
characteristics
of
secondary
storage
include
?
Media
are
the
actual
physical
material
that
holds
the
data
and
progra
ms.
(See
Figure
8-1.)
?
Capacity
measures
how
much
a
particular
storage
medium
can
hold.
?
Storage
devices
are
hardware
that
reads
data
and
programs
from
stor
age
media.
Most
also
write
to
storage
media.
?
Access
speed
measures
the
amount
of
time
required
by
the
storage
de
vice
to
retrieve
data
and
programs.
Most
desktop
microcomputer
systems
have
floppy,
hard,
and
optical
disk
drives.
辅助存储提供永久或非易失性存储。
使用辅助存储设备如软盘驱动器，
数据
和程序可以在电脑关闭后被保存。这是通过从辅助存储设备写入
文件和读取文
件。写入是信息存储在辅助存储设备的过程。读是从辅助存储访问信息的过
程。
本章重点在辅助存储设备上。
辅助存储的一些重要特征包括
?
介质是保存数据和程序的实际物理材料。（见图
8-1
）。
?
容量是测量一个特定的存储介质可以容纳的程度。
?
存储设备是在存储介质上读取数据
和程序的硬件。很多时候也写入到存
储介质。
?
访问速度是测量在存储设备上检索数据和程序所需的时间。
大多数台式微机系统都有软盘，硬盘和光盘驱动。
FLOPPY
DISKS
Floppy
disks
are
portable
or
removable
storage
media.
They
are
typicall
y
I
used
to
store
and
transport
relatively
small
word
processing,
spreadsh
eet,
and
other
types
of
files.
They
use
flexible
flat
circular
pieces
of
Mylar
plastic
that
have
been
coated
with
a
magnetic
material.
Floppy
disk
drive
s
(FDD)
store
data
and
programs
by
altering
the
electromagnetic
charges
on
the
disk's
surface
to
represent
1s
and
0s.
Floppy
disk
drives
retrieve
data
and
programs
by
reading
these
charges
from
the
magnetic
disk.
Char
acters
are
represented
by
positive
(+)
and
negative
(-)
charges
using
the
ASCII,
EBCDIC,
or
Unicode
binary
codes.
For
example,
the
number
3
woul
d
require
a
series
of
8
charges.
(See
Figure
8-2.)
软盘是便携式或移动存储介质。
它们通常是用来储存和运输相对较小
的文字
处理，
电子表格和其他类型的文件。
它们使用柔性扁圆形块塑料里面涂上了一层
磁性材料。软盘驱动器（
FDD
）通过改变磁盘表面上的静电所代表
1
和
0
来存
储数据。软盘驱动器通过读取磁盘上的这些电荷来检索数据和程序。在
ASCII
，
EBCDIC
或
Unicode
二进制代码中字符
由正（
+
）和负（
-
< br>）电荷表示。例如，数
字
3
将需
要
8
个电荷表示。
(
< br>见图
8-2)
P215
TRADITIONAL
FLOPPY
DISK
The
traditional
floppy
disk
is
the
1.44
MB
2HD
3
1/2-inch
disk;
2HD
m
eans
two-sided,
high-density.
Two-sided
indicates
that
data
can
be
stored
on
both
sides
of
the
disk.
Density
refers
to
how
tightly
the
bits
(electrom
agnetic
charges)
can
be
packed
next
to
one
another.
These
disks
have
a
c
apacity
of
1.44
megabytes
—
the
equivalent
of
over
350
typewritten
pages.
Floppy
disks
have
a
thin
exterior
jacket
made
of
hard
plastic
to
protect
the
flexible
disk
inside.
(See
Figure
8-3.)
A
shutter
on
the
disk
slides
to
the
side
to
expose
the
recording
surface.
Labels
provide
users
with
an
ar
ea
to
write
or
document
the
contents
of
the
disk.
The
write-protection
no
tch
has
a
slide
that
opens
and
closes.
In
either
position,
files
can
be
read
from
the
floppy
disk.
When
the
notch
is
closed,
files
can
be
saved
to
th
e
disk.
In
the
open
position,
files
cannot
be
saved
to
the
floppy
disk.
传统的软盘
传统的软盘是
1.44 MB2HD3.5
英寸磁盘
;2HD
意味着两面的，<
/p>
高密度的。
双
面显示，可以在磁盘双面上
存储数据。密度指的是比特（电荷）有多紧密，可以
装到另一个。这些磁盘容量为
1.44
兆字节，相当于
350
多页打字机纸。
软盘有薄的外部硬塑
料制成的护套保护灵活磁盘内部。
（见图
8-3
）
。
磁盘
上的一个快门滑到
另一侧可暴露记录的表面。
标签为用户提供一个区域来写或磁
盘
的文档内容。
写保护缺口有一个打开和关闭的滑道。
在任一位置
，
文件可从软
盘读取。
当缺口是封闭的
，
可将文件保存到磁盘。
在打开的位置，
文件不能被保
存到软盘上。
As
we
discussed
in
Chapter
5,
files
are
stored
and
organized
on
the
fle
xible
disk
according
to
tracks
and
sectors.
Tracks
are
rings
of
concentric
circles
without
visible
grooves.
Each
track
is
divided
into
invisible
wedge-s
haped
sections
called
sectors.
Each
tracks
sector
can
store
up
to
512
byte
s
or
characters.
To
see
how
a
floppy
disk
drive
works,
visit
our
Web
site
at
and
enter
the
keyword
disk.
正如我们在第
5
章讨论的，文件存
储和组织在灵活的磁盘，以磁道和扇区
为依据。
圈形的同心圆环
，
无可见的凹槽。
每个磁道分为无形的楔形部分，
称为
扇区。每个磁道扇区最多可存储
512
个字节或字符。
要看看软盘驱动器如
何工作，
请访问我们的网站
，
然后输入关键字磁盘。
HIGH-CAPACITY
FLOPPY
DISKS
High-
capacity
disks
are
also
known
as
floppy
disk
cartridges.
Like
the
tra
ditional
floppy,
the
high-
capacity
disks
are
3.5
inches
in
diameter.
Howeve
r,
they
are
able
to
store
more
information,
are
thicker,
and
require
specia
l
disk
drives.
The
most
widely
used
high-capacity
disk
is
the
Zip
disk
pro
duced
by
Iomega.
These
disks
typically
have
a
100
MB,
250
MB,
or
750
MB
capacity
—
over
500
times
as
much
as
today's
standard
floppy
disk.
Zi
p
disks
are
typically
used
to
store
multimedia,
database,
large
text,
and
s
preadsheet
files.
(See
Figure
8-4.)
高容量软盘
高容量磁盘也被称为软
盘磁盒。和传统的软盘一样，高容量磁盘的直径为
3.5
英
寸。
然而，
它们能够存储更多的信息且更厚的，
却需要特殊的磁盘驱动器。
最
广泛使用的高容量磁盘是
由
Iomega
生产的
Zip
磁盘。这些磁盘通常有
100
M
B
，
250 MB
或
750 MB
容量，
超过了现在标准软盘的
500
倍。
Zip
磁盘通常用来
存储多媒体，数据库，大型文本
和电子表格文件。（见图
8-4
）
。
P216
At
one
time,
floppy
disks
were
adequate
to
handle
most
storage
require
ment
s
and
fl
oppy
disk
drives
were
a
standard
feature
of
most
system
unit
s.
Fl
oppy
disks,
however,
d
o
not
have
the
capacity
to
store
most
of
today’s
video
and
music
fil
es.
As
a
result,
fl
oppy
disks
and
fl
oppy
disk
drives
are
not
as
widely
used.
有一段
时间，
软盘足以应付大多数的存储需求，
而软盘驱动器则是大多
数系
统单位的标准功能。
然而，
软盘没有容量来存储今天大多数的视频和音乐文件。
因此，软盘和软
盘驱动器不被广泛使用。
HARD
DISKS
Like
floppy
disks,
hard
disks
save
files
by
altering
the
magnetic
charges
of
the
disk's
surface.
While
a
floppy
disk
uses
a
thin
flexible
plastic
disk,
a
hard
disk
uses
thicker,
rigid
metallic
platters
that
are
stacked
one
on
top
of
anot
her
.
Hard
disks
store
and
organize
files
using
tracks,
sectors,
and
cylinders.
A
cylinder
runs
through
each
track
of
a
stack
of
platters.
Although
not
needed
by
floppy
disks
that
have
a
single
platter,
cylinders
are
necessary
to
differenti
ate
files
stored
on
the
same
track
and
sector
of
different
platters.
When
a
h
ard
disk
is
formatted,
tracks,
sectors,
and
cylinders
are
assigned.
硬盘
和软
盘一样，
硬盘通过改变磁盘表面的磁荷来保存文件。
软盘使用薄
的弹性
塑料盘，
而硬盘使用较厚，
刚性
金属盘，
可以逐个叠在另一个上面。
硬盘存储和
组织文件会使用磁道，
扇区和柱面。
一个柱面通过每一
个盘片栈的磁道运行。
虽
然不需要通过带有一个单碟的软盘，<
/p>
但柱面要区分在同一磁道上和扇区不同的盘
片上存储的文件。
当硬盘被格式化，磁道，扇区和柱面被重新分配。
Compared
to
floppy
disks,
hard
disks
are
able
to
store
and
retrieve
informa
tion
much
faster
and
have
a
greater
capacity.
They
are,
however,
sensitive
ins
truments.
Their
read/write
heads
ride
on
a
cushion
of
air
about
0.000001
inc
h
thick.
It
is
so
thin
that
a
smoke
particle,
fingerprint,
dust,
or
human
hair
c
ould
cause
what
is
known
as
a
head
crash.
(See
Figure
8-5.)
A
head
crash
occurs
when
a
read/write
head
BK
makes
contact
with
the
h
ard
disk's
surface
or
with
particles
on
its
surface.
A
head
crash
is
a
disaster
f
or
a
hard
disk.
At
one
time,
head
crashes
were
commonplace.
Now,
fortunate
ly,
they
are
rare.
There
are
three
types
of
hard
disks:
internal
hard
disk,
hard-
disk
cartridge,
and
hard-disk
pack.
与
软盘相比，
硬盘能够存储和检索信息的速度更快，
而且有更大的
容量。
然
而，它们是敏感的仪器。他们的读
/
写磁头乘势而上约
0.000001
英寸厚的空气
垫。
它是如此之薄，烟雾粒子、指纹、灰尘，或人的头发可能会导致所谓的“迎
头相撞”
。
（见图
8-5
）
。
迎头相撞发生在一个读
/
写头
BK
与硬盘的表
面，或在其表面的颗粒接触。
迎头相撞是硬盘的灾难。
磁盘表面
划伤，
部分或全部数据会被破坏。
曾经，
迎头
相撞是司空见惯的事。现在，幸运的是，他们是罕见的。
硬盘的三种类型：内置硬盘，硬盘磁盒和硬盘组。
INTERNAL
HARD
DISK
An
internal
hard
disk
is
located
inside
the
system
unit.
For
most
microcom
puter
systems,
the
internal
hard
disk
drive
is
designated
as
the
C
drive.
It
is
used
to
store
programs
and
large
data
files.
For
example,
nearly
every
microc
omputer
uses
its
internal
hard
disk
to
store
its
operating
system
and
major
a
pplications
such
as
Word
and
Excel.
内部硬盘
一个内置硬盘位于系统单位
。对于大多数微机系统
,
内置硬盘驱动器被指定
为
C:
驱动器。它是用来存储程序和大型数据文件。例
如
,
几乎每一个微机使用其
内置硬盘来
存储它的操作系统和主要的应用程序
,
如
Word
和
Excel
。
Internal
hard
disks
have
two
advantages
over
floppy
disks:
capacity
and
acc
ess
speed.
A
700-gigabyte
internal
hard
disk,
for
instance,
can
hold
almost
as
much
information
as
490,000
standard
floppy
disks.
Because
hard
disks
rotat
e
faster
and
their
read/write
heads
are
closer
to
the
recording
surface,
the
ti
me
required
to
find
and
retrieve
information
(access
speed)
is
much
faster
th
an
for
floppy
disks.
For
these
reasons,
almost
all
of
today's
powerful
applicati
ons
are
designed
to
be
stored
on
and
run
from
an
internal
hard
disk.
To
see
how
a
hard
disk
works,
visit
our
Web
site
at
and
enter
the
keyword
disk.
内置硬盘有两个优势优于软盘
:
容量和访问速度。
例如，
700
g
的内置硬盘可
以容纳如
490000
标准软盘几乎一样多的信息。因为硬盘旋转速度和它们的读
/
写头更接近记录表面
,
所
需查找时间和检索信息
(
访问速度
)<
/p>
比软盘快得多。
由于这
些原因
,
几乎所有的今天的强大的应用程序被设计成从内置硬盘存储和运行。想<
/p>
看看一个硬盘如何工作
,
请访问我们的网
站
,
然后输入关
键字磁盘。
P217
To
ensure
adequate
performance
of
your
internal
hard
disk,
you
should
per
form
routine
maintenance
and
periodically
make
backup
copies
of
all
importa
nt
files.
For
hard-disk
maintenance
and
backup
procedures,
refer
to
Chapter
5
's
coverage
of
the
Windows
utilities
Backup,
Disk
Cleanup,
and
Disk
Defragme
nter
.
确保你的内置硬盘有足够的性能
,<
/p>
你应该执行日常维护和定期做所有重要的
文件的副本备份。对于硬
盘维修和备份过程
,
请参阅第
5
章
Windows
实用程序备
份
,
磁盘清理和磁盘碎片整理程序的报道。
HARD-DISK
CARTRIDGES
While
internal
hard
disks
provide
fast
access,
they
have
a
fixed
amount
of
storage
and
cannot
be
easily
removed
from
the
system
cabinet.
Hard-disk
cart
ridges
are
as
easy
to
remove
as
a
cassette
from
a
videocassette
recorder
.
The
amount
of
storage
available
to
a
computer
system
is
limited
only
by
the
nu
mber
of
cartridges.
硬盘磁盒
虽然内置硬盘提供快速的访问，<
/p>
但是它们有一个固定的存储容量，
且不能轻
易地从系统内核中移除。
硬盘磁盒就像从录像机中取出盒带一样轻松移除。
一个
计算机系统的存储容量仅限制于磁盒的数量。
Hard-disk
cartridges
are
used
primarily
to
complement
an
internal
hard
disk.
Because
the
cartridges
are
easily
removed,
they
are
particularly
useful
to
pro
tect
or
secure
sensitive
information.
Other
uses
for
hard-disk
cartridges
includ
e
backing
up
the
contents
of
the
internal
hard
disk
and
providing
additional
hard-disk
capacity.
硬盘磁
盒主要用来补充内置硬盘。因为磁盒很容易移除
,
它们对保护或
安全
敏感信息特别有用。
硬盘磁盒的其他用途包括备份内置硬盘
的内容和提供额外的
硬盘容量。
Hard-disk
cartridges
for
desktop
computers
have
typical
capacities
of
20
to
100
GB
(gigabytes).
One
of
the
most
widely
used
hard-
disk
cartridges
is
the
Removable
Hard
Disk
from
Iomega.
(See
Figure
8-6.)
Credit
card-size
hard-disk
cartridges
called
PC
Card
hard
disks
are
available
for
notebook
computers
wi
th
typical
capacities
up
to
5
gigabytes.
Two
well-known
PC
Card
hard
disks
ar
e
IBM's
Microdrive
and
Toshiba's
MK5002.
(See
Figure
8-7.)
台式电脑硬盘磁盒的典型容量是
20
到
100
GB
。其中最广泛使用的硬
盘磁
盒是来自
Iomega
的可移动硬
盘。
（见图
8-6
。
< br>）信用卡尺寸的硬盘磁盒叫做
PC
卡
片硬盘，
可让笔记本电脑的典型容量增加
5
GB
。
两个著名的
PC
卡硬盘是
IBM
的
微硬碟机和东芝的
MK5002
。
（见
图
8-7
。
）
P218
HARDHARD-
DISK
PACKS
Hard-
disk
packs
are
removable
storage
devices
used
to
store
massive
amou
nts
of
information.
(See
Figure
8-8.)
Their
capacity
far
exceeds
the
other
type
s
of
hard
disks.
Although
you
may
never
have
seen
one,
it
is
almost
certain
that
you
have
used
them.
Microcomputers
that
have
access
to
the
Intern
et,
minicomputers,
or
mainframes
often
have
access
to
external
hard-disk
packs
through
communication
lines.
Banks
and
credit
card
companies
use
them
to
record
financial
information.
硬盘组
硬盘组是用于存储大量信息的可移
动存储设备。
(
见图
8
-
8)
。它们的容量
远远超过了其他类型的硬盘。尽管你可能从未见过一个
,
那么几乎可以肯定
,
你已
经在使用它
们。微型计算机经常通过通信线路访问外部硬盘组去访问互联网
,
小
型机
,
或大型机。银行和信用卡公
司使用它们来记录财务信息。
Like
internal
hard
disks,
hard-disk
packs
have
multiple
recording
platter
s
aligned
one
above
the
other.
Hard-disk
packs,
however,
use
much
larger
platters,
use
more
platters,
and
are
not
enclosed
in
a
special
container.
Hard-disk
packs
are
stored
in
a
hard
plastic
cover
that
is
removed
when
the
pack
is
mounted
onto
special
drives.
The
drive
rotates
the
pack
and
a
ccess
arms
move
in
and
out
between
the
rotating
platters.
Each
access
ar
m
has
two
read/write
heads.
One
reads
the
disk
surface
above
it;
the
oth
er
reads
the
disk
surface
below
it.
All
the
access
arms
move
in
and
out
t
ogether.
However,
only
one
of
the
read/write
heads
is
activated
at
a
give
n
moment.
A
disk
pack
with
11
disks
provides
20
recording
surfaces.
Thi
s
is
because
the
top
and
bottom
outside
surfaces
of
the
pack
are
not
use
d.
(See
Figure
8-9.)
像内置硬盘一样
,
硬盘组有多个上下对齐的
记录盘片。然而
,
硬盘组使用更大
的盘
片，
使用更多的盘片，
放在一个不封闭的特殊容器。
硬盘组存放在硬塑料盖
中，
当这个组被安装到特殊
的驱动器时，
它将被移除。
驱动器在旋转的盘片之间
使组旋转和接臂移入和移出。每个接臂上有两个读
/
写磁头。一个读取它上面的
磁盘表面，
另一个读取它下面的磁
盘表面。
所有接臂一起移入和移出。
然而，
在
一个给定的时刻只有一个读
/
写
磁头被激活。
有
11
个磁盘的磁盘组提
供了
20
个
记录面。这是因为组的外表
面的顶部和底部是不使用的。
（见图
8-9
）
For
a
summary
of
the
different
types
of
hard
disks,
see
Figure
8-10.
硬盘的不同类型的总结，见图
8-10
。
P219
PERFORMANCE
ENHANCEMENTS
Three
ways
to
improve
the
performance
of
hard
disks
are
disk
caching,
redundant
arrays
of
inexpensive
disks,
and
file
compression/decompressio
n.
Disk
caching
improves
hard-disk
performance
by
anticipating
data
needs.
It
performs
a
function
similar
to
cache
memory
discussed
in
Chapter
6.
While
cache
memory
improves
processing
by
acting
as
a
temporary
high-s
peed
holding
area
between
memory
and
the
CPU,
disk
caching
improves
p
rocessing
by
acting
as
a
temporary
high-speed
holding
area
between
a
sec
ondary
storage
device
and
the
CPU.
Disk
caching
requires
a
combination
o
f
hardware
and
software.
During
idle
processing
time,
frequently
used
dat
a
is
read
from
the
hard
disk
into
memory
(cache).
When
needed,
the
dat
a
is
then
accessed
directly
from
memory.
The
transfer
rate
from
memory
is
much
faster
than
from
the
hard
disk.
As
a
result,
overall
system
perfor
mance
is
often
increased
by
as
much
as
30
percent.
性能加强
提高硬盘性能的三种方法是磁盘缓存，磁盘阵列，文件压缩
/
解
压。
磁盘缓存，
通过预测数据的需求
提高硬盘的性能。
它执行的功能类似于在第
6
< br>章中讨论的内存缓存。
内存缓存提高处理，
是通过在内存
和
CPU
之间充当一个
临时高速缓冲区
，而磁盘缓存提高处理，是通过在辅助存储装置和
CPU
之间充
当一个临时高速缓冲区。
磁盘缓存要求硬件和软件的组合。
在空闲处理时间，
经
常使用的数据从硬盘读
取到内存
（缓存）
。
当需要时，
该数据然后从内存中直接
访问。
内存的传送速
率比从硬盘快得多。
结果是，
整个系统的性能通常增加
30
％
以上。
Redundant
arrays
of
inexpensive
disks
(RAID)
improve
performance
by
expanding
external
storage,
improving
access
speed,
and
providing
reliable
storage.
Several
inexpensive
hard-disk
drives
are
connected
to
one
anoth
er.
These
connections
can
be
by
a
network
or
within
specialized
RAID
de
vices.
(See
Figure
8-11.)
The
connected
hard-disk
drives
are
related
or
gr
ouped
together,
and
the
computer
system
interacts
with
the
RAID
system
as
though
it
were
a
single
large-capacity
hard-disk
drive.
The
result
is
ex
panded
storage
capability,
fast
access
speed,
and
high
reliability.
For
these
reasons,
RAID
is
often
used
by
Internet
servers
and
large
organizations.
磁盘阵列（
RAID
）提高性能，通过扩大外部存储设备，提高访问速度和提
供可靠的存储。
一些廉价的硬盘驱动器被连接到其他。
这些连接可以是在一个网
络内或专门的
RAID
设备之间。
（见图
8-11
）
相接的
硬盘驱动器可以是相关的或
组合在一起，计算机系统与
RAID
系统进行交互，就好像它是一个单一的大容量
硬盘驱动器。
结果是被扩展的存储能力，
快存取速度和高可靠性。
由于这些原因，
RAID
是经常被使用在网络服务器和
大型组织。
File
compression
and
file
decompression
increase
storage
capacity
by
re
ducing
the
amount
of
space
required
to
store
data
and
programs.
File
co
mpression
is
not
limited
to
hard-disk
systems.
It
is
frequently
used
to
co
mpress
files
on
floppy
disks
as
well.
File
compression
also
helps
to
speed
up
transmission
of
files
from
one
computer
system
to
another.
Sending
a
nd
receiving
compressed
files
across
the
Internet
is
a
common
activity.
通过减
少所需的空间来存储数据和程序，
文件压缩与文件解压能增加存储容
量。
文件压缩并不限于硬盘系统。
它也经常可以使用在软盘
上压缩文件。
文件压
缩也可以帮助加快从一台计算机系统到另一
台的文件的传输。
在互联网上发送和
接收压缩文件是一种常见的
活动。
File
compression
programs
scan
files
for
ways
to
reduce
the
amount
of
required
storage.
One
way
is
to
search
for
repeating
patterns.
The
repeat
ing
patterns
are
replaced
with
a
token,
leaving
enough
tokens
so
that
the
original
can
be
rebuilt
or
decompressed.
These
programs
often
shrink
file
s
to
a
quarter
of
their
original
size.
To
learn
more
about
file
compression,
visit
Our
Web
site
at
and
enter
the
keyword
c
ompression.
You
can
compress
and
decompress
files
using
specialized
utili
ties
such
as
WinZip
from
Nico
Mak
Computing
and
PKZip
from
PKWare.
Or,
if
these
specialized
utilities
are
not
available,
you
can
use
utility
progr
ams
in
Windows
XP.
For
a
summary
of
performance
enhancement
techniq
ues,
see
Figure
8-12.
文件压
缩程序用扫描文件的方法来减少所需的存储量。
一种方法是搜索重复
图案。
重复图案被替换为一个图案，
会留出足够的图案，<
/p>
使原来的可以重建或解
压。
这些程序通常
压缩文件到其原始大小的四分之一。
要了解更多相关的文件压
缩
，请访问我们的网站
，然后输入关键字压缩。你可
以使用专门的工具如
Nico
Mak
Computing
的
WinZip
与
PKWare
的
PKZI
P
来压
缩和解压文件。或者，如果这些专用程序不实用，你可以
使用
Windows
XP
中
的实用程序。性能增强技术的总结，见图
8-12
。
P220
OPTICAL
DISCS
Today’s
optical
discs
can
hold
over
50
gigabytes
of
data.
(See
Figure
8
-
13.)
That
is
the
disc
equivalent
of
millions
of
typewritten
pages
or
a
med
ium-sized
library
all
on
a
single
disc.
Optical
discs
are
having
a
great
imp
act
on
storage
today,
but
we
are
probably
only
beginning
to
see
their
eff
ects.
光学磁盘
如今的光学磁盘可容纳超过
50
千兆字节的数据。
（见图
8-13
）。这相当于
数以百万计的打字机打印的页面或一个中等规模的图书馆，存放在一张光盘上。
光盘在
今天的存储上有很大的影响，但我们可能才刚刚开始看到效果。
In
optical-disc
technology,
a
laser
beam
alters
the
surface
of
a
plastic
o
r
metallic
disc
to
represent
data.
Unlike
floppy
and
hard
disks,
which
use
magnetic
charges
to
represent
1s
and
0s,
optical
discs
use
reflected
light.
The
1s
and
0s
are
represented
by
flat
areas
called
lands
and
bumpy
are
as
called
pits
on
the
disc
surface.
The
disc
is
read
by
an
optical
disc
driv
e
using
a
laser
that
projects
a
tiny
beam
of
light
on
these
areas.
The
am
ount
of
reflected
light
determines
whether
the
area
represents
a
1
or
a
0.
To
see
how
an
optical
disc
drive
works,
visit
our
Web
site
at
and
enter
the
keyword
optical.
在光学
磁盘技术中，
激光束改变塑料的表面或金属盘来表示数据。
不像
软盘
和硬盘，它们使用磁荷代表
1
和<
/p>
0
，光学磁盘使用反射光。
“
1
”和“
0
”代表
在光盘表面上被称为台的平坦区域和被称为坑的凹坑区域。
光盘读取是通过光学
磁盘驱动器使用激光的一束微小光束投影在这些领域
。
光的反射数量决定是否代
表一个
1<
/p>
或
0
。
想看看光
学磁盘驱动器如何工作，
请访问我们的网站
，然后输入关键字光学。
Like
floppy
and
hard
disks,
optical
discs
use
tracks
and
sectors
to
orga
nize
and
store
files.
Unlike
the
concentric
tracks
and
wedge-shaped
sector
s
Used
for
floppy
and
hard
disks,
however,
optical
discs
typically
use
a
si
ngle
track
that
spirals
toward
the
center
of
the
disc.
This
single
track
is
divided
into
equally
sized
sectors.
像软盘和硬盘一
样，
光学磁盘使用磁道和扇区来组织和存储文件。
然而，
不
同于软盘和硬盘使用的同心磁道和楔形扇区，
光学磁盘通常使用一个单磁道，
螺
旋向着盘中心。这种单磁道
被分成大小相同的扇区。
COMPACT
DISC
Compact
disc,
or
as
it
is
better
known,
CD,
is
one
of
the
most
widely
u
sed
optical
formats.
CD
drives
are
standard
on
many
microcomputer
syste
ms.
Typically,
CD
drives
can
store
from
650
MB
(megabytes)
to
1
GB
(gig
abyte)
of
data
on
one
side
of
a
CD.
There
are
three
basic
types
of
CDs:
read
only,
write
once,
and
rewritabl
e:
高密度
光盘
高密度
光盘更广为人知，
CD
是最广泛
使用的光盘格式之一。
CD
驱动器是许多
微机系统的标准。
通常情况下，
CD
驱动器可以在
CD
的一侧上存储
650
MB
（兆
字节）到
1
GB
（千兆字节）的数据。
CD
的三种基本类型：只读，一次写入和可擦写：