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姓名：岳群杰
班级：信安
2006
级
3
班
学号：
2006122105
Personal computer
What is
personal computer
There
have been many kinds of computer systems according
to their size,such as su-
percomputers,mainframe computers
,minicomputers and personal o-
mputers
are special,high capacity computers used by very
large organization principa
lly for
research purposes ,among which are oil exploration
and worldwide weather fo-
recasting
.Mainframe computers (or mainframes )are
large,powerful computers that
many people can use at the same time
.They are also expensive systems that are used
for very large processing
tasks and perform many important business and
government
applicatoions .Minicomputers
are smaller and more compact systems ,and fewer
opra-
tors can use them compared with a
mainframe computer .They are usually found in m
edium-size businesses or in divisions
within a large organization ,for example in gov-
vernment department.
Personal computers-also
called microcomputers-are small,self-contained
computers
that fit on a
desktop and usually only used by one are the
least exepensiv
e type,and are widely
used in business for a business for a variety of
tasks,such as wor
d
–
processing ,small database
management ,and are also used as ho
me
computers,for family budgeting and similar jobs,as
well as for games.
Protable compuers
Another important
development in personal computer technology is
that the portabl
e computers have been
widely used .A small , portable personal computer
is light and
small enough
to hold on your lap. The computer is smaller than
a luggage but larger th
an a
notebook,and is also called a laptop or notebook
computer .A portable computer
usually weighs between three to eight
pounds,and when folded shut is about the size o
f a small briefcase .So it offers the
user considerable freedom. The user can work his
computer on train ,or on an
airplane ,or on safari in Africa.
Portable
computers can be plugged in or run on
batteries,although the batteries mu
st
be recharged very few hours .Battery power is a
critical bottleneck,computers use a
thin,mance and blocking further product
le computer use a thin,
1
lightweight display screen
called a flat-panel display or a LCD
monitor,rather than the
cathode
ray
tube
technology
of
large
personal
computers.
Portable
computer
displays
vary
widely
in
quality.
Typically,
their
display
screens
show
fewer
lines
than
displays
on
larger
personal
computers
and
can
be
difficult
to
read
in
bright
light.
Portable
computers
are
self-contained units, having their own
CPUs, memory, and many have modems and CD-ROM
drives as well.
While
more
expensive
than
a
desktop
computer
with
equivalent
computing
power,
a
portable computer van be
ideal for the go-user who needs a second personal
computer when
he is out of desktop
computers, since they can not be expanded or
modified easily should your
computing
needs change. Also, the display is inferior to
standard video graphics array (VGA)
displays, although active matrix
displays almost compete well except for size.
The first portable computers, such as
the Osborne
Ⅰ
and
Compaq
Ⅱ
, are best described
as
“
luggeables
”
. These computers weighed
in at more than 25 pounds and could not carried
comfortably
for
more
than
a
short
distance.
Today
’
s
portable
computers,
the
laptop
and
notebook computers are much smaller and
lighter.
Systems
Using
Miscroprocessors
Electronic
systems
are
used
for
handling
information
in
the
most
general
sense;
this
information may be telephone
conversation, instrument reading or a
company
’
s accounts, but
in
each
case
the
same
main
types
of
operation
are
involved;
the
processing,
storage
and
transmission of
information. In conventional electronic design
these operations are combined
at
the
function
level;
for
example
a
counter,
whether
electronic
or
mechanical,
stores
the
current
count
and
increments
it
by
one
as
required.
A
system
such
as
an
electronic
clock
which
employs
counters
has
its
storage
and
processing
capabilities
spread
throughout
the
system because each counter is able to
store and process numbers.
Present
day
microprocessor
based
systems
depart
from
this
conventional
approach
by
separating the three
functions of processing, storage, and transmission
into different sections
of
the
system.
This
partitioning
into
three
main
functions
was
devised
by
V
on
Neumann
during
the
1940s,and
was
not
conceived
especially
for
microcomputers.
Almost
every
computer ever made has been designed
with this structure, and despite the enormous
range in
their physical forms ,
they have all been of
essentially the same basic design.
In
a
microprocessor
based
system
the
processing
will
be
performed
in
the
microprocessor
itself
.
The
storage
will
be
by
means
of
memory
circuits
and
the
communication
of
information
into
and
out
of
the
system
will
be
by
means
of
special
2
input/output(I/O)
circuits.
It
would be impossible to
identify
a particular
piece of hardware
which
performed
the
counting
in
a
microprocessor
based
clock
because
the
time
would
be
stored in the memory and incremented at
regular intervals by the microprocessor. However,
the software which defined the
system
’
s behavior would
contain sections that performed as
counters.
The
apparently
rather
abstract
approach
to
the
architecture
of
the
microprocessor
and
its
associated
circuits
allows
it
to
be
very
flexible
in
use,
since
the
system
is
defined
almost entirely in
software. The design process is largely one of
software engineering, and the
similar
problems
of construction and
maintenance which occur in
conventional
engineering
are encountered
when producing software .
Figure 15.1
illustrates how these three sections within a
microcomputer are connected in
terms of
the communication of information within the
transfer of information between itself
and the memory and input /ouput
external connections relate to the rest(that is
the non-computer part ) of the
engineering system.
Although
only
one
storage
section
has
been
shown
in
the
diagram
,
in
practice
two
distinct types of memory RAM and ROM
are used. In each case, the
word
”
memory
”
is rather
inappropriate since a computer memory
is more like a filing cabinet in concept;
information is
stored in a set of
numbered
“
boxes
”<
/p>
and it is referenced by the serial
number of the
“
box
”
in
question.
Microcomputers use RAM(Random Access
Memory)into which data can be written and
from which data can be read again when
needed. This date can be read back from the memory
in any sequence desired, and not
necessarily the same order in which it was
written, hence the
“
random
”
access memory.
Another type of ROM (Read Only Memory) is used to
hold fixed
patterns of information
which cannot be affected by the microprocessor;
these patterns are not
lost
when
power
is
removed
and
are
normally
used
to
hold
the
program
which
defines
the
behavior of a microprocessor based
system. ROMs can be read like RAMs , but unlike
RAMs
they cannot be used to store
variable information . Some ROMs have their data
patterns put in
during
manufacture,
while
others
are
programmable
by
the
user
by
means
of
special
equipment and are called programmable
ROMs. The widely used
programmable ROMs
are
erasable
by
means
of
special
ultravioletlamps
and
are
referred
to
as
EPROMs,
short
for
Erasable
Programmable
Read
Only
Memories .Other
new
types
of
device
can
be
erased
electrically
without
the
need
for
ultravioletlight
,
which
are
called
Electrically
Erasable
Programmable Read
Only Memories, EEPROMs.
The
microprocessor processes data under the
control of the porogram,
controlling the
flow of
information to and from memory and input/output
devices .Some input/output devices
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