<s>
A	O
computer	B-Application
architecture	I-Application
simulator	I-Application
is	O
a	O
program	B-Application
that	O
simulates	O
the	O
execution	B-General_Concept
of	O
computer	B-General_Concept
architecture	I-General_Concept
.	O
</s>
<s>
Computer	B-Application
architecture	I-Application
simulators	I-Application
are	O
used	O
for	O
the	O
following	O
purposes	O
:	O
</s>
<s>
Computer	B-Application
architecture	I-Application
simulators	I-Application
can	O
be	O
classified	O
into	O
many	O
different	O
categories	O
depending	O
on	O
the	O
context	O
.	O
</s>
<s>
Scope	O
:	O
Microarchitecture	B-Application
simulators	I-Application
model	O
the	O
microprocessor	B-Architecture
and	O
its	O
components	O
.	O
</s>
<s>
Detail	O
:	O
Functional	O
simulators	O
,	O
such	O
as	O
instruction	B-Application
set	I-Application
simulators	I-Application
,	O
achieve	O
the	O
same	O
function	O
as	O
modeled	O
components	O
.	O
</s>
<s>
Execution-driven	O
simulators	O
allow	O
dynamic	O
change	O
of	O
instructions	O
to	O
be	O
executed	O
depending	O
on	O
different	O
input	O
data	O
.	O
</s>
<s>
A	O
full-system	O
simulator	O
is	O
execution-driven	O
architecture	O
simulation	O
at	O
such	O
a	O
level	O
of	O
detail	O
that	O
complete	O
software	O
stacks	O
from	O
real	O
systems	O
can	O
run	O
on	O
the	O
simulator	O
without	O
any	O
modification	O
.	O
</s>
<s>
A	O
full	B-Application
system	I-Application
simulator	I-Application
provides	O
virtual	O
hardware	O
that	O
is	O
independent	O
of	O
the	O
nature	O
of	O
the	O
host	O
computer	O
.	O
</s>
<s>
The	O
full-system	O
model	O
typically	O
includes	O
processor	O
cores	O
,	O
peripheral	B-Device
devices	I-Device
,	O
memories	B-General_Concept
,	O
interconnection	O
buses	O
,	O
and	O
network	B-Architecture
connections	O
.	O
</s>
<s>
Emulators	B-Application
are	O
full	B-Application
system	I-Application
simulators	I-Application
that	O
imitate	O
obsolete	O
hardware	O
instead	O
of	O
under	O
development	O
hardware	O
.	O
</s>
<s>
The	O
defining	O
property	O
of	O
full-system	O
simulation	O
compared	O
to	O
an	O
instruction	B-Application
set	I-Application
simulator	I-Application
is	O
that	O
the	O
model	O
allows	O
real	O
device	B-Application
drivers	I-Application
and	O
operating	B-General_Concept
systems	I-General_Concept
to	O
be	O
run	O
,	O
not	O
just	O
single	O
programs	O
.	O
</s>
<s>
Thus	O
,	O
full-system	O
simulation	O
makes	O
it	O
possible	O
to	O
simulate	O
individual	O
computers	O
and	O
networked	O
computer	O
nodes	O
with	O
all	O
their	O
software	O
,	O
from	O
network	B-Architecture
device	B-Application
drivers	I-Application
to	O
operating	B-General_Concept
systems	I-General_Concept
,	O
network	B-Protocol
stacks	I-Protocol
,	O
middleware	B-General_Concept
,	O
servers	O
,	O
and	O
application	B-Application
programs	I-Application
.	O
</s>
<s>
Full	B-Application
system	I-Application
simulation	I-Application
can	O
speed	O
the	O
system	O
development	O
process	O
by	O
making	O
it	O
easier	O
to	O
detect	O
,	O
recreate	O
and	O
repair	O
flaws	O
.	O
</s>
<s>
The	O
use	O
of	O
multi-core	B-Architecture
processors	I-Architecture
is	O
driving	O
the	O
need	O
for	O
full	B-Application
system	I-Application
simulation	I-Application
,	O
because	O
it	O
can	O
be	O
extremely	O
difficult	O
and	O
time-consuming	O
to	O
recreate	O
and	O
debug	O
errors	O
without	O
the	O
controlled	O
environment	O
provided	O
by	O
virtual	O
hardware	O
.	O
</s>
<s>
A	O
cycle-accurate	B-Application
simulator	I-Application
is	O
a	O
computer	B-Application
program	I-Application
that	O
simulates	O
a	O
microarchitecture	B-General_Concept
on	O
a	O
cycle-by-cycle	O
basis	O
.	O
</s>
<s>
In	O
contrast	O
an	O
instruction	B-Application
set	I-Application
simulator	I-Application
simulates	O
an	O
instruction	B-General_Concept
set	I-General_Concept
architecture	I-General_Concept
usually	O
faster	O
but	O
not	O
cycle-accurate	O
to	O
a	O
specific	O
implementation	O
of	O
this	O
architecture	O
;	O
they	O
are	O
often	O
used	O
when	O
emulating	B-Application
older	O
hardware	O
,	O
where	O
time	O
precision	O
is	O
important	O
for	O
legacy	O
reasons	O
.	O
</s>
<s>
Often	O
,	O
a	O
cycle-accurate	B-Application
simulator	I-Application
is	O
used	O
when	O
designing	O
new	O
microprocessorsthey	O
can	O
be	O
tested	O
,	O
and	O
benchmarked	O
accurately	O
(	O
including	O
running	O
full	O
operating	B-General_Concept
system	I-General_Concept
,	O
or	O
compilers	O
)	O
without	O
actually	O
building	O
a	O
physical	O
chip	O
,	O
and	O
easily	O
change	O
design	O
many	O
times	O
to	O
meet	O
expected	O
plan	O
.	O
</s>
<s>
Cycle-accurate	B-Application
simulators	I-Application
must	O
ensure	O
that	O
all	O
operations	O
are	O
executed	O
in	O
the	O
proper	O
virtual	O
(	O
or	O
real	O
if	O
it	O
is	O
possible	O
)	O
timebranch	O
prediction	O
,	O
cache	O
misses	O
,	O
fetches	O
,	O
pipeline	O
stalls	O
,	O
thread	O
context	O
switching	O
,	O
and	O
many	O
other	O
subtle	O
aspects	O
of	O
microprocessors	B-Architecture
.	O
</s>
