<s>
Random	B-General_Concept
access	I-General_Concept
(	O
more	O
precisely	O
and	O
more	O
generally	O
called	O
direct	O
access	O
)	O
is	O
the	O
ability	O
to	O
access	O
an	O
arbitrary	O
element	O
of	O
a	O
sequence	O
in	O
equal	O
time	O
or	O
any	O
datum	O
from	O
a	O
population	O
of	O
addressable	B-General_Concept
elements	O
roughly	O
as	O
easily	O
and	O
efficiently	O
as	O
any	O
other	O
,	O
no	O
matter	O
how	O
many	O
elements	O
may	O
be	O
in	O
the	O
set	O
.	O
</s>
<s>
In	O
computer	B-General_Concept
science	I-General_Concept
it	O
is	O
typically	O
contrasted	O
to	O
sequential	B-General_Concept
access	I-General_Concept
which	O
requires	O
data	O
to	O
be	O
retrieved	O
in	O
the	O
order	O
it	O
was	O
stored	O
.	O
</s>
<s>
the	O
coordinates	O
at	O
which	O
it	O
is	O
located	O
,	O
such	O
as	O
its	O
row	O
and	O
column	O
(	O
or	O
its	O
track	O
and	O
record	O
number	O
on	O
a	O
magnetic	B-General_Concept
drum	I-General_Concept
)	O
.	O
</s>
<s>
At	O
first	O
,	O
the	O
term	O
"	O
random	B-General_Concept
access	I-General_Concept
"	O
was	O
used	O
because	O
the	O
process	O
had	O
to	O
be	O
capable	O
of	O
finding	O
records	O
no	O
matter	O
in	O
which	O
sequence	O
they	O
were	O
required	O
.	O
</s>
<s>
The	O
opposite	O
is	O
sequential	B-General_Concept
access	I-General_Concept
,	O
where	O
a	O
remote	O
element	O
takes	O
longer	O
time	O
to	O
access	O
.	O
</s>
<s>
A	O
more	O
modern	O
example	O
is	O
a	O
cassette	O
tape	O
(	O
sequential	O
one	O
must	O
fast	O
forward	O
through	O
earlier	O
songs	O
to	O
get	O
to	O
later	O
ones	O
)	O
and	O
a	O
CD	B-Device
(	O
direct	O
access	O
one	O
can	O
skip	O
to	O
the	O
track	O
wanted	O
,	O
knowing	O
that	O
it	O
would	O
be	O
the	O
one	O
retrieved	O
)	O
.	O
</s>
<s>
In	O
data	B-General_Concept
structures	I-General_Concept
,	O
direct	O
access	O
implies	O
the	O
ability	O
to	O
access	O
any	O
entry	O
in	O
a	O
list	O
in	O
constant	O
time	O
(	O
independent	O
of	O
its	O
position	O
in	O
the	O
list	O
and	O
of	O
the	O
list	O
's	O
size	O
)	O
.	O
</s>
<s>
Very	O
few	O
data	B-General_Concept
structures	I-General_Concept
can	O
make	O
this	O
guarantee	O
other	O
than	O
arrays	O
(	O
and	O
related	O
structures	O
like	O
dynamic	B-Data_Structure
arrays	I-Data_Structure
)	O
.	O
</s>
<s>
Direct	O
access	O
is	O
required	O
,	O
or	O
at	O
least	O
valuable	O
,	O
in	O
many	O
algorithms	O
such	O
as	O
binary	O
search	O
,	O
integer	B-Algorithm
sorting	I-Algorithm
,	O
or	O
certain	O
versions	O
of	O
sieve	B-Algorithm
of	I-Algorithm
Eratosthenes	I-Algorithm
.	O
</s>
<s>
Other	O
data	B-General_Concept
structures	I-General_Concept
,	O
such	O
as	O
linked	B-Data_Structure
lists	I-Data_Structure
,	O
sacrifice	O
direct	O
access	O
to	O
permit	O
efficient	O
inserts	O
,	O
deletes	O
,	O
or	O
re-ordering	O
of	O
data	O
.	O
</s>
<s>
Self-balancing	B-Data_Structure
binary	I-Data_Structure
search	I-Data_Structure
trees	I-Data_Structure
may	O
provide	O
an	O
acceptable	O
compromise	O
,	O
where	O
access	O
time	O
is	O
not	O
equal	O
for	O
all	O
members	O
of	O
a	O
collection	O
,	O
but	O
the	O
maximum	O
time	O
to	O
retrieve	O
a	O
given	O
member	O
grows	O
only	O
logarithmically	O
with	O
its	O
size	O
.	O
</s>
