<s>
In	O
computing	O
,	O
as	O
well	O
as	O
in	O
non-computing	O
contexts	O
,	O
a	O
file	B-General_Concept
sequence	I-General_Concept
is	O
a	O
well-ordered	O
,	O
(	O
finite	O
)	O
collection	O
of	O
files	O
,	O
usually	O
related	O
to	O
each	O
other	O
in	O
some	O
way	O
.	O
</s>
<s>
In	O
computing	O
,	O
file	B-General_Concept
sequences	I-General_Concept
should	O
ideally	O
obey	O
some	O
kind	O
of	O
locality	B-General_Concept
of	I-General_Concept
reference	I-General_Concept
principle	O
,	O
so	O
that	O
not	O
only	O
all	O
the	O
files	O
belonging	O
to	O
the	O
same	O
sequence	O
ought	O
to	O
be	O
locally	O
referenced	O
to	O
each	O
other	O
,	O
but	O
they	O
also	O
obey	O
that	O
as	O
much	O
as	O
is	O
their	O
proximity	O
with	O
respect	O
to	O
the	O
ordering	B-Algorithm
relation	I-Algorithm
.	O
</s>
<s>
Explicit	O
file	B-General_Concept
sequences	I-General_Concept
are	O
,	O
in	O
fact	O
,	O
sequences	O
whose	O
filenames	O
all	O
end	O
with	O
a	O
numeric	O
or	O
alphanumeric	O
tag	O
in	O
the	O
end	O
(	O
excluding	O
file	B-Operating_System
extension	O
)	O
.	O
</s>
<s>
The	O
aforementioned	O
locality	B-General_Concept
of	I-General_Concept
reference	I-General_Concept
usually	O
pertains	O
either	O
to	O
the	O
data	O
,	O
the	O
metadata	O
(	O
e.g.	O
</s>
<s>
In	O
the	O
latter	O
acception	O
it	O
is	O
better	O
to	O
speak	O
about	O
file	B-Operating_System
contiguity	O
(	O
see	O
below	O
)	O
.	O
</s>
<s>
Every	O
GUI	B-Application
program	O
shows	O
contents	O
of	O
folders	B-Application
by	O
usually	O
ordering	O
its	O
files	O
according	O
to	O
some	O
criteria	O
,	O
mostly	O
related	O
to	O
the	O
files	O
 '	O
metadata	O
,	O
like	O
the	O
filename	O
.	O
</s>
<s>
ideally	O
be	O
placed	O
before	O
file10.ext	O
,	O
like	O
GNOME	B-Language
Files	I-Language
and	O
Thunar	B-Language
do	O
,	O
whereas	O
,	O
alphanumerically	O
,	O
it	O
comes	O
after	O
(	O
more	O
on	O
that	O
later	O
)	O
.	O
</s>
<s>
Other	O
criteria	O
exist	O
,	O
like	O
ordering	O
files	O
by	O
their	O
file	B-Operating_System
type	O
(	O
or	O
by	O
their	O
extension	O
)	O
and	O
,	O
if	O
the	O
same	O
type	O
,	O
by	O
either	O
filename	O
or	O
last-access	O
date	O
,	O
and	O
so	O
on	O
.	O
</s>
<s>
For	O
this	O
reason	O
,	O
when	O
a	O
file	B-General_Concept
sequence	I-General_Concept
has	O
a	O
more	O
strong	O
locality	B-General_Concept
of	I-General_Concept
reference	I-General_Concept
,	O
particularly	O
when	O
it	O
is	O
related	O
to	O
their	O
actual	O
contents	O
,	O
it	O
is	O
better	O
to	O
highlight	O
this	O
fact	O
by	O
letting	O
their	O
well-ordering	O
induce	O
an	O
alphanumeric	O
ordering	O
of	O
the	O
filenames	O
too	O
.	O
</s>
<s>
That	O
is	O
the	O
case	O
of	O
explicit	O
file	B-General_Concept
sequences	I-General_Concept
.	O
</s>
<s>
Explicit	O
file	B-General_Concept
sequences	I-General_Concept
have	O
the	O
same	O
filename	O
(	O
including	O
file	B-Operating_System
extensions	O
in	O
order	O
to	O
confirm	O
their	O
contents	O
 '	O
locality	B-General_Concept
of	I-General_Concept
reference	I-General_Concept
)	O
except	O
for	O
the	O
final	O
part	O
(	O
excluding	O
the	O
extension	O
)	O
,	O
which	O
is	O
a	O
sequence	O
of	O
either	O
numeric	O
,	O
alphanumeric	O
or	O
purely	O
alphabetical	O
characters	O
to	O
force	O
a	O
specific	O
ordering	O
;	O
such	O
sequences	O
should	O
also	O
be	O
ideally	O
located	O
all	O
within	O
the	O
same	O
directory	B-Application
.	O
</s>
<s>
In	O
this	O
sense	O
any	O
files	O
sharing	O
the	O
same	O
filename	O
(	O
and	O
possibly	O
extension	O
)	O
,	O
only	O
differing	O
by	O
the	O
sequence	O
number	O
at	O
the	O
end	O
of	O
the	O
filename	O
,	O
automatically	O
belong	O
to	O
the	O
same	O
file	B-General_Concept
sequence	I-General_Concept
,	O
at	O
least	O
when	O
they	O
are	O
located	O
in	O
the	O
same	O
folder	O
.	O
</s>
<s>
It	O
is	O
also	O
part	O
of	O
many	O
naming	O
conventions	O
that	O
number-indexed	O
file	B-General_Concept
sequences	I-General_Concept
(	O
in	O
any	O
number	O
base	O
)	O
containing	O
as	O
many	O
files	O
as	O
to	O
span	O
at	O
most	O
a	O
fixed	O
number	O
of	O
digits	O
,	O
make	O
use	O
of	O
"	O
trailing	O
zeroes	O
"	O
in	O
their	O
filenames	O
so	O
that	O
:	O
</s>
<s>
non-smart	O
alphanumeric	O
orderings	O
,	O
like	O
those	O
of	O
operating	O
systems	O
 '	O
GUIs	B-Application
,	O
do	O
not	O
erroneously	O
permute	O
them	O
within	O
the	O
sequence	O
.	O
</s>
<s>
To	O
better	O
explain	O
the	O
latter	O
point	O
,	O
consider	O
that	O
,	O
strictly	O
speaking	O
,	O
file1.ext	O
(	O
1st	O
file	B-Operating_System
in	O
the	O
sequence	O
)	O
comes	O
alphanumerically	O
after	O
file100.ext	O
,	O
which	O
is	O
actually	O
the	O
hundredth	O
.	O
</s>
<s>
By	O
renaming	O
the	O
first	O
file	B-Operating_System
to	O
file001.ext	O
with	O
two	O
trailing	O
zeroes	O
,	O
the	O
problem	O
is	O
universally	O
solved	O
.	O
</s>
<s>
Examples	O
of	O
explicit	O
file	B-General_Concept
sequences	I-General_Concept
include	O
:	O
file00000.ext	O
,	O
file00001.ext	O
,	O
file00002.ext	O
,	O
,	O
file02979.ext	O
(	O
five	O
trailing	O
zeroes	O
)	O
,	O
and	O
another	O
with	O
a	O
hexadecimal	O
ordering	O
of	O
256	O
files	O
tag_00.ext	O
,	O
tag_01.ext	O
,	O
,	O
tag_09.ext	O
,	O
tag_0A.ext	O
,	O
...	O
,	O
tag_0F.ext	O
,	O
tag_10.ext	O
,	O
...	O
,	O
tag_0F.ext	O
,	O
...	O
,	O
tag_FF.ext	O
(	O
with	O
just	O
one	O
trailing	O
zero	O
)	O
.	O
</s>
<s>
Software	O
and	O
programming	O
conventions	O
usually	O
represent	O
a	O
file	B-General_Concept
sequence	I-General_Concept
as	O
a	O
single	O
virtual	O
file	B-Operating_System
object	O
,	O
whose	O
name	O
is	O
comprehensively	O
written	O
in	O
C-like	O
formatted-string	O
notation	O
to	O
represent	O
where	O
the	O
sequence	O
number	O
is	O
located	O
in	O
the	O
filename	O
and	O
what	O
is	O
its	O
formatting	O
.	O
</s>
<s>
Note	O
,	O
however	O
,	O
that	O
such	O
notation	O
is	O
usually	O
not	O
valid	O
at	O
operating	O
system	O
and	O
command-line	B-Application
interface	I-Application
levels	O
,	O
because	O
the	O
'	O
%	O
 '	O
character	O
is	O
neither	O
a	O
valid	O
regular	B-Language
expression	I-Language
nor	O
a	O
universally	O
legal	O
filename	O
character	O
:	O
that	O
notation	O
just	O
stands	O
as	O
a	O
placeholder	B-Language
for	O
the	O
virtual	O
file-like	O
representing	O
the	O
whole	O
explicit	O
file	B-General_Concept
sequence	I-General_Concept
.	O
</s>
<s>
Notable	O
software	O
packages	O
acknowledging	O
explicit	O
file	B-General_Concept
sequences	I-General_Concept
as	O
single	O
filesystem	B-Application
objects	O
,	O
rather	O
typical	O
in	O
the	O
Audio/Video	O
post-production	O
industry	O
(	O
see	O
below	O
)	O
,	O
are	O
found	O
among	O
products	O
by	O
Autodesk	O
,	O
Quantel	O
,	O
daVinci	O
,	O
DVS	O
,	O
as	O
well	O
as	O
Adobe	B-Operating_System
After	I-Operating_System
Effects	I-Operating_System
.	O
</s>
<s>
A	O
file	B-General_Concept
sequence	I-General_Concept
located	O
within	O
a	O
mass	B-Device
storage	I-Device
device	I-Device
is	O
said	O
to	O
be	O
contiguous	O
if	O
:	O
</s>
<s>
every	O
file	B-Operating_System
in	O
the	O
sequence	O
is	O
unfragmented	O
,	O
i.e.	O
</s>
<s>
each	O
file	B-Operating_System
is	O
stored	O
in	O
one	O
contiguous	O
and	O
ordered	O
piece	O
of	O
storage	O
space	O
(	O
ideally	O
in	O
one	O
or	O
multiple	O
,	O
but	O
contiguous	O
,	O
extents	B-Application
)	O
;	O
</s>
<s>
consecutive	O
files	O
in	O
the	O
sequence	O
occupy	O
contiguous	O
portions	O
of	O
storage	O
space	O
(	O
extents	B-Application
,	O
yet	O
consistently	O
with	O
their	O
file	B-Operating_System
ordering	O
)	O
.	O
</s>
<s>
File	B-Operating_System
contiguity	O
is	O
a	O
more	O
practical	O
requirement	O
for	O
file	B-General_Concept
sequences	I-General_Concept
than	O
just	O
their	O
locality	B-General_Concept
of	I-General_Concept
reference	I-General_Concept
,	O
because	O
it	O
is	O
related	O
to	O
the	O
storage	O
medium	O
hosting	O
the	O
whole	O
sequence	O
than	O
to	O
the	O
sequence	O
itself	O
(	O
or	O
its	O
metadata	O
)	O
.	O
</s>
<s>
At	O
the	O
same	O
time	O
,	O
it	O
is	O
a	O
"	O
high-level	O
"	O
feature	O
,	O
because	O
it	O
is	O
not	O
related	O
to	O
the	O
physical	O
and	O
technical	O
details	O
of	O
mass	B-Device
storage	I-Device
itself	O
:	O
particularly	O
,	O
file	B-Operating_System
contiguity	O
is	O
realized	O
in	O
different	O
ways	O
according	O
to	O
the	O
storage	O
device	O
's	O
architecture	O
and	O
actual	O
filesystem	B-Application
structure	O
.	O
</s>
<s>
At	O
"	O
low	O
level	O
"	O
,	O
each	O
file	B-Operating_System
in	O
a	O
contiguous	O
sequence	O
must	O
be	O
placed	O
in	O
contiguous	O
blocks	O
,	O
in	O
spite	O
of	O
reserved	O
areas	O
or	O
special	O
metadata	O
required	O
by	O
the	O
filesystem	B-Application
(	O
like	O
inodes	B-Application
or	O
inter-sector	O
headers	O
)	O
actually	O
interleaving	O
them	O
.	O
</s>
<s>
File	B-Operating_System
contiguity	O
is	O
,	O
in	O
most	O
practical	O
applications	O
,	O
"	O
invisible	O
"	O
at	O
operating-system	O
or	O
user	O
levels	O
,	O
since	O
all	O
the	O
files	O
in	O
a	O
sequence	O
are	O
always	O
available	O
to	O
applications	O
in	O
the	O
same	O
way	O
,	O
regardless	O
of	O
their	O
physical	O
location	O
on	O
the	O
storage	O
device	O
(	O
due	O
to	O
operating	O
systems	O
hiding	O
the	O
filesystem	B-Application
internals	O
to	O
higher-level	O
services	O
)	O
.	O
</s>
<s>
Indeed	O
,	O
file	B-Operating_System
contiguity	O
may	O
be	O
related	O
to	O
I/O	O
performance	O
when	O
the	O
sequence	O
is	O
to	O
be	O
read	O
or	O
written	O
in	O
the	O
shortest	O
time	O
possible	O
.	O
</s>
<s>
below	O
)	O
,	O
data	O
in	O
a	O
file	B-General_Concept
sequence	I-General_Concept
must	O
be	O
accessed	O
in	O
the	O
same	O
order	O
as	O
the	O
file	B-General_Concept
sequence	I-General_Concept
itself	O
;	O
in	O
other	O
contexts	O
,	O
a	O
"	O
random	O
"	O
access	O
to	O
the	O
sequence	O
may	O
be	O
required	O
.	O
</s>
<s>
In	O
both	O
cases	O
,	O
most	O
professional	O
filesystems	B-Application
provide	O
faster	O
access	O
strategies	O
to	O
contiguous	O
files	O
than	O
non-contiguous	O
ones	O
.	O
</s>
<s>
When	O
a	O
file	B-General_Concept
sequence	I-General_Concept
is	O
not	O
contiguous	O
,	O
it	O
is	O
said	O
to	O
be	O
scattered	O
,	O
since	O
its	O
files	O
are	O
stored	O
in	O
sparse	O
locations	O
on	O
the	O
storage	O
device	O
.	O
</s>
<s>
File	B-Operating_System
scattering	O
is	O
the	O
process	O
of	O
allocating	O
(	O
or	O
re-allocating	O
)	O
a	O
file	B-General_Concept
sequence	I-General_Concept
as	O
being	O
(	O
or	O
becoming	O
)	O
uncontiguous	O
.	O
</s>
<s>
That	O
is	O
often	O
associated	O
with	O
file	B-Application
fragmentation	I-Application
too	O
,	O
where	O
each	O
file	B-Operating_System
is	O
also	O
stored	O
in	O
several	O
,	O
non-contiguous	O
blocks	O
;	O
mechanisms	O
contributing	O
to	O
the	O
former	O
are	O
usually	O
a	O
common	O
cause	O
to	O
the	O
latter	O
too	O
.	O
</s>
<s>
The	O
act	O
of	O
reducing	O
file	B-Operating_System
scattering	O
by	O
means	O
of	O
allocating	O
(	O
in	O
the	O
first	O
place	O
)	O
or	O
moving	O
(	O
for	O
already-stored	O
data	O
)	O
files	O
in	O
the	O
same	O
sequence	O
near	O
together	O
on	O
the	O
storage	O
medium	O
is	O
called	O
(	O
file	B-Operating_System
)	O
file	B-Operating_System
descattering	O
.	O
</s>
<s>
A	O
few	O
defragmentation	B-Application
strategies	O
and	O
dedicated	O
software	O
are	O
able	O
to	O
both	O
defragment	B-Application
single	O
files	O
and	O
descatter	O
file	B-General_Concept
sequences	I-General_Concept
.	O
</s>
<s>
There	O
are	O
many	O
contexts	O
which	O
explicit	O
file	B-General_Concept
sequences	I-General_Concept
are	O
particularly	O
important	O
in	O
:	O
incremental	O
backups	O
,	O
periodic	O
logs	O
and	O
multimedia	O
files	O
captured	O
or	O
created	O
with	O
a	O
chronological	O
locality	B-General_Concept
of	I-General_Concept
reference	I-General_Concept
.	O
</s>
<s>
In	O
the	O
latter	O
case	O
,	O
explicit	O
file	B-Operating_System
numbering	O
is	O
extremely	O
important	O
in	O
order	O
to	O
provide	O
both	O
software	O
and	O
end	O
users	O
a	O
way	O
to	O
discern	O
the	O
consequentiality	O
of	O
the	O
contents	O
stored	O
therein	O
.	O
</s>
<s>
For	O
example	O
,	O
digital	O
cameras	O
and	O
similar	O
devices	O
save	O
all	O
the	O
picture	O
files	O
in	O
the	O
same	O
folder	O
(	O
until	O
it	O
either	O
reaches	O
its	O
maximum	O
file-number	O
capacity	O
,	O
or	O
a	O
new	O
event	O
like	O
midnight-coming	O
or	O
device-switching	O
takes	O
place	O
)	O
with	O
a	O
final	O
number	O
sequence	O
:	O
it	O
would	O
be	O
very	O
unpractical	O
to	O
choose	O
a	O
filename	O
for	O
each	O
taken	O
shot	O
on	O
the	O
very	O
shooting	O
time	O
,	O
so	O
the	O
camera	O
firmware/software	O
picks	O
one	O
which	O
is	O
perfectly	O
identifiable	O
by	O
its	O
sequence	O
number	O
.	O
</s>
<s>
A	O
typical	O
example	O
where	O
explicit	O
file	B-General_Concept
sequences	I-General_Concept
,	O
as	O
well	O
as	O
their	O
contiguity	O
,	O
becomes	O
crucial	O
is	O
in	O
the	O
digital	O
intermediate	O
(	O
DI	O
)	O
workflow	O
for	O
motion	O
picture	O
and	O
video	O
industries	O
.	O
</s>
<s>
Usually	O
video	O
data	O
are	O
acquired	O
from	O
either	O
a	O
digital	O
video	O
camera	O
or	O
a	O
motion	O
picture	O
film	O
scanner	O
and	O
stored	O
into	O
file	B-General_Concept
sequences	I-General_Concept
(	O
as	O
much	O
as	O
a	O
common	O
photographic	O
camera	O
does	O
)	O
and	O
need	O
to	O
be	O
post-produced	O
in	O
several	O
steps	O
,	O
including	O
at	O
least	O
editing	O
,	O
conforming	O
and	O
colour-correction	O
.	O
</s>
<s>
Uncompressed	O
data	O
,	O
because	O
any	O
lossy	B-Algorithm
compression	I-Algorithm
,	O
which	O
is	O
common	O
in	O
most	O
finalized	O
products	O
,	O
introduces	O
unacceptable	O
quality	O
losses	O
.	O
</s>
<s>
Frame-per-file	O
data	O
management	O
,	O
because	O
common	O
post-production	O
operations	O
imply	O
the	O
shortest	O
seek-times	O
ever	O
;	O
"	O
fast-forwarding	O
"	O
or	O
"	O
rewinding	O
"	O
to	O
a	O
specific	O
(	O
key	O
)	O
frame	O
is	O
much	O
faster	O
if	O
done	O
at	O
filesystem	B-Application
level	O
rather	O
than	O
within	O
a	O
huge	O
,	O
possibly	O
fragmented	B-Application
video	O
file	B-Operating_System
;	O
every	O
frame	O
is	O
then	O
stored	O
in	O
a	O
single	O
file	B-Operating_System
as	O
a	O
still	O
digital	O
picture	O
.	O
</s>
<s>
Unambiguous	O
frames	O
 '	O
ordering	O
,	O
for	O
obvious	O
reasons	O
,	O
which	O
is	O
best	O
accomplished	O
grouping	O
all	O
the	O
files	O
together	O
with	O
explicit	O
file	B-Operating_System
numbering	O
.	O
</s>
<s>
File	B-Operating_System
contiguity	O
,	O
because	O
many	O
filesystem	B-Application
architectures	O
employ	O
higher	O
I/O	O
speeds	O
if	O
transferring	O
data	O
on	O
contiguous	O
areas	O
of	O
the	O
storage	O
,	O
whereas	O
random	O
allocation	O
might	O
prevent	O
real-time	O
or	O
better	O
loading	O
performances	O
.	O
</s>
<s>
Consider	O
that	O
a	O
single	O
frame	O
in	O
a	O
DI	O
project	O
is	O
currently	O
from	O
9MB	O
to	O
48MB	O
large	O
(	O
depending	O
upon	O
resolution	B-General_Concept
and	O
colour-depth	O
)	O
,	O
whereas	O
video	O
refresh	O
rate	O
is	O
commonly	O
24	O
or	O
25	O
frames	O
per	O
second	O
(	O
if	O
not	O
faster	O
)	O
;	O
any	O
storage	O
required	O
for	O
real-time	O
playing	O
such	O
contents	O
thus	O
needs	O
a	O
minimum	O
overall	O
throughput	O
of	O
220MB/s	O
to	O
1.2GB/s	O
,	O
respectively	O
.	O
</s>
<s>
With	O
those	O
numbers	O
,	O
all	O
the	O
above	O
requirements	O
(	O
particularly	O
file	B-Operating_System
contiguity	O
,	O
given	O
nowadays	O
storage	O
performances	O
)	O
become	O
strictly	O
mandatory	O
.	O
</s>
