<s>
Relaxed	B-Operating_System
sequential	I-Operating_System
in	O
computer	B-General_Concept
science	I-General_Concept
is	O
an	O
execution	B-Device
model	I-Device
describing	O
the	O
ability	O
for	O
a	O
parallel	B-Operating_System
program	I-Operating_System
to	O
run	O
sequentially	O
.	O
</s>
<s>
If	O
a	O
parallel	B-Operating_System
program	I-Operating_System
has	O
a	O
valid	O
sequential	O
execution	O
it	O
is	O
said	O
to	O
follow	O
a	O
relaxed	B-Operating_System
sequential	I-Operating_System
execution	B-Device
model	I-Device
.	O
</s>
<s>
The	O
word	O
relaxed	O
refers	O
to	O
the	O
notion	O
that	O
serial	O
programs	O
are	O
actually	O
overly	O
constrained	O
by	O
implicit	O
serial	O
dependencies	O
(	O
such	O
as	O
the	O
program	O
counter	O
)	O
and	O
that	O
one	O
can	O
introduce	O
as	O
much	O
parallelism	B-Operating_System
as	O
possible	O
without	O
removing	O
the	O
ability	O
to	O
run	O
sequentially	O
.	O
</s>
<s>
Most	O
parallel	B-Operating_System
programs	I-Operating_System
can	O
run	O
sequentially	O
but	O
will	O
benefit	O
from	O
parallelism	B-Operating_System
when	O
it	O
is	O
present	O
.	O
</s>
<s>
It	O
is	O
possible	O
to	O
design	O
programs	O
that	O
require	O
parallelism	B-Operating_System
for	O
correct	O
behavior	O
.	O
</s>
<s>
Programs	O
designed	O
to	O
require	O
concurrency	O
will	O
have	O
performance	O
issues	O
when	O
the	O
number	O
of	O
required	O
threads	O
exceeds	O
the	O
number	O
of	O
hardware	O
threads	O
because	O
time	B-Operating_System
slicing	I-Operating_System
artifacts	O
can	O
hit	O
hard	O
.	O
</s>
