<s>
A	O
disk	B-Application
image	I-Application
is	O
a	O
snapshot	O
of	O
a	O
storage	O
device	O
's	O
structure	O
and	O
data	O
typically	O
stored	O
in	O
one	O
or	O
more	O
computer	O
files	O
on	O
another	O
storage	O
device	O
.	O
</s>
<s>
Traditionally	O
,	O
disk	B-Application
images	I-Application
were	O
bit-by-bit	O
copies	O
of	O
every	O
sector	O
on	O
a	O
hard	B-Device
disk	I-Device
often	O
created	O
for	O
digital	O
forensic	O
purposes	O
,	O
but	O
it	O
is	O
now	O
common	O
to	O
only	O
copy	O
allocated	O
data	O
to	O
reduce	O
storage	O
space	O
.	O
</s>
<s>
Compression	B-General_Concept
and	O
deduplication	B-General_Concept
are	O
commonly	O
used	O
to	O
reduce	O
the	O
size	O
of	O
the	O
image	O
file	O
set	O
.	O
</s>
<s>
Disk	B-Application
imaging	I-Application
is	O
done	O
for	O
a	O
variety	O
of	O
purposes	O
including	O
digital	O
forensics	O
,	O
cloud	B-Architecture
computing	I-Architecture
,	O
system	B-Application
administration	I-Application
,	O
as	O
part	O
of	O
a	O
backup	B-Protocol
strategy	O
,	O
and	O
legacy	O
emulation	B-Application
as	O
part	O
of	O
a	O
digital	O
preservation	O
strategy	O
.	O
</s>
<s>
Disk	B-Application
images	I-Application
can	O
be	O
made	O
in	O
a	O
variety	O
of	O
formats	O
depending	O
on	O
the	O
purpose	O
.	O
</s>
<s>
Virtual	O
disk	B-Application
images	I-Application
(	O
such	O
as	O
VHD	O
and	O
VMDK	O
)	O
are	O
intended	O
to	O
be	O
used	O
for	O
cloud	B-Architecture
computing	I-Architecture
,	O
ISO	B-General_Concept
images	I-General_Concept
are	O
intended	O
to	O
emulate	O
optical	B-Device
media	I-Device
and	O
raw	B-General_Concept
disk	I-General_Concept
images	I-General_Concept
are	O
used	O
for	O
forensic	O
purposes	O
.	O
</s>
<s>
Proprietary	O
formats	O
are	O
typically	O
used	O
by	O
disk	B-Application
imaging	I-Application
software	O
.	O
</s>
<s>
Despite	O
the	O
benefits	O
of	O
disk	B-Application
imaging	I-Application
the	O
storage	O
costs	O
can	O
be	O
high	O
,	O
management	O
can	O
be	O
difficult	O
and	O
they	O
can	O
be	O
time	O
consuming	O
to	O
create	O
.	O
</s>
<s>
Disk	B-Application
images	I-Application
were	O
originally	O
(	O
in	O
the	O
late	O
1960s	O
)	O
used	O
for	O
backup	B-Protocol
and	O
disk	B-Application
cloning	I-Application
of	O
mainframe	O
disk	O
media	O
.	O
</s>
<s>
Disk	B-Application
images	I-Application
became	O
much	O
more	O
popular	O
when	O
floppy	O
disk	O
media	O
became	O
popular	O
,	O
where	O
replication	O
or	O
storage	O
of	O
an	O
exact	O
structure	O
was	O
necessary	O
and	O
efficient	O
,	O
especially	O
in	O
the	O
case	O
of	O
copy	B-Application
protected	I-Application
floppy	O
disks	O
.	O
</s>
<s>
Disk	B-Application
image	I-Application
creation	O
is	O
called	O
disk	B-Application
imaging	I-Application
and	O
is	O
often	O
time	O
consuming	O
,	O
even	O
with	O
a	O
fast	O
computer	O
,	O
because	O
the	O
entire	O
disk	O
must	O
be	O
copied	O
.	O
</s>
<s>
Typically	O
,	O
disk	B-Application
imaging	I-Application
requires	O
a	O
third	O
party	O
disk	B-Application
imaging	I-Application
program	O
or	O
backup	B-Protocol
software	O
.	O
</s>
<s>
The	O
software	O
required	O
varies	O
according	O
to	O
the	O
type	O
of	O
disk	B-Application
image	I-Application
that	O
needs	O
to	O
be	O
created	O
.	O
</s>
<s>
For	O
example	O
,	O
RawWrite	O
and	O
WinImage	O
create	O
floppy	B-General_Concept
disk	I-General_Concept
image	I-General_Concept
files	O
for	O
MS-DOS	B-Application
and	O
Microsoft	B-Application
Windows	I-Application
.	O
</s>
<s>
In	O
Unix	B-Application
or	O
similar	B-Operating_System
systems	I-Operating_System
the	O
dd	B-Application
program	O
can	O
be	O
used	O
to	O
create	O
raw	B-General_Concept
disk	I-General_Concept
images	I-General_Concept
.	O
</s>
<s>
Apple	B-Operating_System
Disk	I-Operating_System
Copy	I-Operating_System
can	O
be	O
used	O
on	O
Classic	B-Application
Mac	I-Application
OS	I-Application
and	O
macOS	B-Application
systems	O
to	O
create	O
and	O
write	O
disk	B-Application
image	I-Application
files	O
.	O
</s>
<s>
Authoring	O
software	O
for	O
CDs/DVDs	O
such	O
as	O
Nero	B-Application
Burning	I-Application
ROM	I-Application
can	O
generate	O
and	O
load	O
disk	B-Application
images	I-Application
for	O
optical	B-Device
media	I-Device
.	O
</s>
<s>
A	O
virtual	O
disk	O
writer	O
or	O
virtual	O
burner	O
is	O
a	O
computer	O
program	O
that	O
emulates	B-Application
an	O
actual	O
disc	O
authoring	O
device	O
such	O
as	O
a	O
CD	B-Device
writer	O
or	O
DVD	O
writer	O
.	O
</s>
<s>
Instead	O
of	O
writing	O
data	O
to	O
an	O
actual	O
disc	O
,	O
it	O
creates	O
a	O
virtual	O
disk	B-Application
image	I-Application
.	O
</s>
<s>
A	O
virtual	O
burner	O
,	O
by	O
definition	O
,	O
appears	O
as	O
a	O
disc	O
drive	O
in	O
the	O
system	O
with	O
writing	O
capabilities	O
(	O
as	O
opposed	O
to	O
conventional	O
disc	O
authoring	O
programs	O
that	O
can	O
create	O
virtual	O
disk	B-Application
images	I-Application
)	O
,	O
thus	O
allowing	O
software	O
that	O
can	O
burn	O
discs	O
to	O
create	O
virtual	O
discs	O
.	O
</s>
<s>
Unlike	O
disk	B-Application
imaging	I-Application
for	O
other	O
purposes	O
,	O
digital	O
forensic	O
applications	O
take	O
a	O
bit-by-bit	O
copy	O
to	O
ensure	O
forensic	O
soundness	O
.	O
</s>
<s>
In	O
cloud	B-Architecture
computing	I-Architecture
,	O
creating	O
a	O
disk	B-Application
image	I-Application
of	O
optical	B-Device
media	I-Device
or	O
a	O
hard	B-Device
disk	I-Device
drive	I-Device
is	O
typically	O
done	O
to	O
make	O
the	O
content	O
available	O
to	O
one	O
or	O
more	O
virtual	B-Architecture
machines	I-Architecture
.	O
</s>
<s>
Virtual	B-Architecture
machines	I-Architecture
emulate	O
a	O
CD/DVD	O
drive	O
by	O
reading	O
an	O
ISO	B-General_Concept
image	I-General_Concept
.	O
</s>
<s>
A	O
hard	B-Device
disk	I-Device
drive	I-Device
or	O
solid-state	B-Device
drive	I-Device
in	O
a	O
virtual	B-Architecture
machine	I-Architecture
is	O
implemented	O
as	O
a	O
disk	B-Application
image	I-Application
(	O
i.e.	O
</s>
<s>
either	O
the	O
VHD	O
format	O
used	O
by	O
Microsoft	O
's	O
Hyper-V	O
,	O
the	O
VDI	O
format	O
used	O
by	O
Oracle	B-Application
Corporation	I-Application
's	O
VirtualBox	B-Operating_System
,	O
the	O
VMDK	O
format	O
used	O
for	O
VMware	O
virtual	B-Architecture
machines	I-Architecture
,	O
or	O
the	O
QCOW	O
format	O
used	O
by	O
QEMU	B-Application
)	O
.	O
</s>
<s>
Virtual	O
hard	B-Application
disk	I-Application
images	I-Application
tend	O
to	O
be	O
stored	O
as	O
either	O
a	O
collection	O
of	O
files	O
(	O
where	O
each	O
one	O
is	O
typically	O
2GB	O
in	O
size	O
)	O
,	O
or	O
as	O
a	O
single	O
file	O
.	O
</s>
<s>
Virtual	B-Architecture
machines	I-Architecture
treat	O
the	O
image	O
set	O
as	O
a	O
physical	O
drive	O
.	O
</s>
<s>
Disk	B-Application
imaging	I-Application
is	O
commonly	O
used	O
to	O
deploy	O
the	O
same	O
configuration	O
across	O
workstations	O
.	O
</s>
<s>
Typically	O
,	O
disk	B-Application
imaging	I-Application
software	O
(	O
such	O
as	O
Ghost	B-Application
or	O
Clonezilla	B-Language
)	O
is	O
used	O
to	O
make	O
an	O
image	O
of	O
a	O
completely	O
configured	O
system	O
.	O
</s>
<s>
This	O
image	O
is	O
then	O
written	O
to	O
a	O
computer	O
's	O
hard	B-Device
disk	I-Device
which	O
is	O
sometimes	O
described	O
as	O
restoring	O
an	O
image	O
.	O
</s>
<s>
This	O
restoration	O
is	O
sometimes	O
done	O
over	O
a	O
computer	O
network	O
using	O
multicasting	O
or	O
BitTorrent	B-Protocol
to	O
devices	O
that	O
need	O
to	O
have	O
their	O
configuration	O
restored	O
.	O
</s>
<s>
Disk	B-Application
imaging	I-Application
requires	O
for	O
all	O
devices	O
to	O
be	O
identical	O
and	O
provides	O
no	O
flexibility	O
in	O
adjusting	O
the	O
configuration	O
.	O
</s>
<s>
Network-based	O
image	O
deployment	O
typically	O
uses	O
a	O
PXE	B-Device
server	O
to	O
boot	O
a	O
minimal	O
operating	O
system	O
over	O
the	O
network	O
that	O
contains	O
the	O
necessary	O
components	O
to	O
image	O
or	O
restore	O
storage	O
media	O
in	O
a	O
computer	O
.	O
</s>
<s>
This	O
is	O
usually	O
used	O
in	O
conjunction	O
with	O
a	O
DHCP	O
server	O
to	O
automate	O
the	O
configuration	O
of	O
network	O
parameters	O
including	O
IP	B-Protocol
addresses	I-Protocol
.	O
</s>
<s>
Typically	O
,	O
multicasting	O
,	O
broadcasting	B-Operating_System
or	O
unicasting	B-Protocol
is	O
used	O
to	O
restore	O
an	O
image	O
to	O
many	O
computers	O
at	O
a	O
time	O
but	O
these	O
approaches	O
do	O
not	O
work	O
well	O
if	O
one	O
or	O
more	O
computers	O
experience	O
a	O
problem	O
such	O
as	O
UDP	B-Protocol
packet	I-Protocol
loss	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
some	O
imaging	O
solutions	O
instead	O
use	O
the	O
BitTorrent	B-Protocol
protocol	I-Protocol
to	O
transfer	O
the	O
data	O
.	O
</s>
<s>
A	O
disk	B-Application
image	I-Application
contains	O
all	O
files	O
,	O
faithfully	O
replicating	O
all	O
data	O
,	O
including	O
file	B-Application
attributes	I-Application
and	O
the	O
file	B-Application
fragmentation	I-Application
state	O
.	O
</s>
<s>
For	O
this	O
reason	O
,	O
it	O
is	O
also	O
used	O
for	O
backing	O
up	O
optical	B-Device
media	I-Device
(	O
CDs	B-Device
and	O
DVDs	O
,	O
etc	O
.	O
</s>
<s>
)	O
,	O
and	O
allows	O
the	O
exact	O
and	O
efficient	O
recovery	O
after	O
experimenting	O
with	O
modifications	O
to	O
a	O
system	O
or	O
virtual	B-Architecture
machine	I-Architecture
.	O
</s>
<s>
Typically	O
,	O
disk	B-Application
imaging	I-Application
can	O
be	O
used	O
to	O
quickly	O
restore	O
an	O
entire	O
system	O
to	O
an	O
operational	O
state	O
after	O
a	O
disaster	O
.	O
</s>
<s>
Emulators	B-Application
frequently	O
use	O
disk	B-Application
images	I-Application
to	O
emulate	O
floppy	O
disks	O
that	O
have	O
been	O
preserved	O
.	O
</s>
<s>
Emulation	B-Application
also	O
allows	O
existing	O
disk	B-Application
images	I-Application
to	O
be	O
put	O
into	O
a	O
usable	O
form	O
even	O
though	O
the	O
data	O
contained	O
in	O
the	O
image	O
is	O
no	O
longer	O
readable	O
without	O
emulation	B-Application
.	O
</s>
<s>
Disk	B-Application
images	I-Application
can	O
sometimes	O
be	O
slower	O
than	O
reading	O
from	O
the	O
disk	O
directly	O
because	O
of	O
a	O
performance	O
overhead	O
.	O
</s>
<s>
For	O
example	O
,	O
prior	O
to	O
Windows	O
8	O
,	O
third	O
party	O
software	O
was	O
required	O
to	O
mount	O
disk	B-Application
images	I-Application
.	O
</s>
<s>
Disk	B-Application
imaging	I-Application
is	O
time	O
consuming	O
and	O
the	O
space	O
requirements	O
are	O
high	O
.	O
</s>
<s>
Disk	B-Application
imaging	I-Application
can	O
be	O
slow	O
,	O
especially	O
for	O
older	O
storage	O
devices	O
.	O
</s>
<s>
Floppy	O
disks	O
read	O
and	O
write	O
much	O
slower	O
than	O
hard	B-Device
disks	I-Device
.	O
</s>
<s>
In	O
some	O
cases	O
,	O
disk	B-Application
imaging	I-Application
can	O
fail	O
due	O
to	O
bad	O
sectors	O
or	O
physical	O
wear	O
and	O
tear	O
on	O
the	O
source	O
device	O
.	O
</s>
<s>
Utilities	O
such	O
as	O
dd	B-Application
are	O
not	O
designed	O
to	O
recognize	O
or	O
cope	O
with	O
failures	O
.	O
</s>
