<s>
Sequential	B-General_Concept
access	I-General_Concept
is	O
a	O
term	O
describing	O
a	O
group	O
of	O
elements	O
(	O
such	O
as	O
data	O
in	O
a	O
memory	O
array	O
or	O
a	O
disk	B-Device
file	O
or	O
on	O
magnetic-tape	B-Architecture
data	I-Architecture
storage	I-Architecture
)	O
being	O
accessed	O
in	O
a	O
predetermined	O
,	O
ordered	O
sequence	O
.	O
</s>
<s>
It	O
is	O
the	O
opposite	O
of	O
random	B-General_Concept
access	I-General_Concept
,	O
the	O
ability	O
to	O
access	O
an	O
arbitrary	O
element	O
of	O
a	O
sequence	O
as	O
easily	O
and	O
efficiently	O
as	O
any	O
other	O
at	O
any	O
time	O
.	O
</s>
<s>
Sequential	B-General_Concept
access	I-General_Concept
is	O
sometimes	O
the	O
only	O
way	O
of	O
accessing	O
the	O
data	O
,	O
for	O
example	O
if	O
it	O
is	O
on	O
a	O
tape	O
.	O
</s>
<s>
There	O
is	O
no	O
consistent	O
definition	O
in	O
computer	B-General_Concept
science	I-General_Concept
of	O
sequential	B-General_Concept
access	I-General_Concept
or	O
sequentiality	O
.	O
</s>
<s>
In	O
data	B-General_Concept
structures	I-General_Concept
,	O
a	O
data	B-General_Concept
structure	I-General_Concept
is	O
said	O
to	O
have	O
sequential	B-General_Concept
access	I-General_Concept
if	O
one	O
can	O
only	O
visit	O
the	O
values	O
it	O
contains	O
in	O
one	O
particular	O
order	O
.	O
</s>
<s>
The	O
canonical	O
example	O
is	O
the	O
linked	B-Data_Structure
list	I-Data_Structure
.	O
</s>
<s>
Indexing	O
into	O
a	O
list	O
that	O
has	O
sequential	B-General_Concept
access	I-General_Concept
requires	O
O(n )	O
time	O
,	O
where	O
n	O
is	O
the	O
index	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
many	O
algorithms	O
such	O
as	O
quicksort	B-Algorithm
and	O
binary	O
search	O
degenerate	O
into	O
bad	O
algorithms	O
that	O
are	O
even	O
less	O
efficient	O
than	O
their	O
naive	O
alternatives	O
;	O
these	O
algorithms	O
are	O
impractical	O
without	O
random	B-General_Concept
access	I-General_Concept
.	O
</s>
<s>
On	O
the	O
other	O
hand	O
,	O
some	O
algorithms	O
,	O
typically	O
those	O
that	O
do	O
not	O
have	O
index	O
,	O
require	O
only	O
sequential	B-General_Concept
access	I-General_Concept
,	O
such	O
as	O
mergesort	B-Algorithm
,	O
and	O
face	O
no	O
penalty	O
.	O
</s>
