<s>
In	O
software	O
development	O
,	O
distributed	B-Protocol
version	I-Protocol
control	I-Protocol
(	O
also	O
known	O
as	O
distributed	B-Protocol
revision	I-Protocol
control	I-Protocol
)	O
is	O
a	O
form	O
of	O
version	B-Architecture
control	I-Architecture
in	O
which	O
the	O
complete	O
codebase	B-General_Concept
,	O
including	O
its	O
full	O
history	O
,	O
is	O
mirrored	O
on	O
every	O
developer	O
's	O
computer	O
.	O
</s>
<s>
Compared	O
to	O
centralized	O
version	B-Architecture
control	I-Architecture
,	O
this	O
enables	O
automatic	O
management	O
branching	B-General_Concept
and	O
merging	B-General_Concept
,	O
speeds	O
up	O
most	O
operations	O
(	O
except	O
pushing	O
and	O
pulling	O
)	O
,	O
improves	O
the	O
ability	O
to	O
work	O
offline	O
,	O
and	O
does	O
not	O
rely	O
on	O
a	O
single	O
location	O
for	O
backups	O
.	O
</s>
<s>
Git	B-Application
,	O
the	O
world	O
's	O
most	O
popular	O
version	B-Architecture
control	I-Architecture
system	I-Architecture
,	O
is	O
a	O
distributed	B-Protocol
version	I-Protocol
control	I-Protocol
system	I-Protocol
.	O
</s>
<s>
In	O
2010	O
,	O
software	O
development	O
author	O
Joel	O
Spolsky	O
described	O
distributed	B-Protocol
version	I-Protocol
control	I-Protocol
systems	I-Protocol
as	O
"	O
possibly	O
the	O
biggest	O
advance	O
in	O
software	O
development	O
technology	O
in	O
the	O
 [ past ] 	O
ten	O
years	O
"	O
.	O
</s>
<s>
Distributed	B-Protocol
version	I-Protocol
control	I-Protocol
systems	I-Protocol
(	O
DVCS	O
)	O
use	O
a	O
peer-to-peer	O
approach	O
to	O
version	B-Architecture
control	I-Architecture
,	O
as	O
opposed	O
to	O
the	O
client	B-Operating_System
–	I-Operating_System
server	I-Operating_System
approach	O
of	O
centralized	O
systems	O
.	O
</s>
<s>
Distributed	B-Protocol
revision	I-Protocol
control	I-Protocol
synchronizes	O
repositories	O
by	O
transferring	O
patches	B-Application
from	O
peer	O
to	O
peer	O
.	O
</s>
<s>
There	O
is	O
no	O
single	O
central	O
version	O
of	O
the	O
codebase	B-General_Concept
;	O
instead	O
,	O
each	O
user	O
has	O
a	O
working	O
copy	O
and	O
the	O
full	O
change	O
history	O
.	O
</s>
<s>
On	O
FOSS	B-License
software	O
projects	O
it	O
is	O
much	O
easier	O
to	O
create	O
a	O
project	B-Application
fork	I-Application
from	O
a	O
project	O
that	O
is	O
stalled	O
because	O
of	O
leadership	O
conflicts	O
or	O
design	O
disagreements	O
.	O
</s>
<s>
Initial	O
checkout	O
of	O
a	O
repository	O
is	O
slower	O
as	O
compared	O
to	O
checkout	O
in	O
a	O
centralized	O
version	B-Architecture
control	I-Architecture
system	I-Architecture
,	O
because	O
all	O
branches	O
and	O
revision	O
history	O
are	O
copied	O
to	O
the	O
local	O
machine	O
by	O
default	O
.	O
</s>
<s>
Additional	O
storage	O
required	O
for	O
every	O
user	O
to	O
have	O
a	O
complete	O
copy	O
of	O
the	O
complete	O
codebase	B-General_Concept
history	O
.	O
</s>
<s>
Increased	O
exposure	O
of	O
the	O
code	B-General_Concept
base	I-General_Concept
since	O
every	O
participant	O
has	O
a	O
locally	O
vulnerable	O
copy	O
.	O
</s>
<s>
Team	B-Application
Foundation	I-Application
Server	I-Application
and	O
Visual	O
Studio	O
Team	O
Services	O
now	O
host	O
centralized	O
and	O
distributed	B-Protocol
version	I-Protocol
control	I-Protocol
repositories	O
via	O
hosting	O
Git	B-Application
.	O
</s>
<s>
Similarly	O
,	O
some	O
distributed	O
systems	O
now	O
offer	O
features	O
that	O
mitigate	O
the	O
issues	O
of	O
checkout	O
times	O
and	O
storage	O
costs	O
,	O
such	O
as	O
the	O
Virtual	B-Application
File	I-Application
System	I-Application
for	I-Application
Git	I-Application
developed	O
by	O
Microsoft	O
to	O
work	O
with	O
very	O
large	O
codebases	B-General_Concept
,	O
which	O
exposes	O
a	O
virtual	O
file	O
system	O
that	O
downloads	O
files	O
to	O
local	O
storage	O
only	O
as	O
they	O
are	O
needed	O
.	O
</s>
<s>
The	O
distributed	O
model	O
is	O
generally	O
better	O
suited	O
for	O
large	O
projects	O
with	O
partly	O
independent	O
developers	O
,	O
such	O
as	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
project	O
,	O
because	O
developers	O
can	O
work	O
independently	O
and	O
submit	O
their	O
changes	O
for	O
merge	B-General_Concept
(	O
or	O
rejection	O
)	O
.	O
</s>
<s>
The	O
integrator	B-Protocol
workflow	I-Protocol
is	O
the	O
most	O
widely	O
used	O
.	O
</s>
<s>
In	O
a	O
truly	O
distributed	O
project	O
,	O
such	O
as	O
Linux	B-Operating_System
,	O
every	O
contributor	O
maintains	O
their	O
own	O
version	O
of	O
the	O
project	O
,	O
with	O
different	O
contributors	O
hosting	O
their	O
own	O
respective	O
versions	O
and	O
pulling	O
in	O
changes	O
from	O
other	O
users	O
as	O
needed	O
,	O
resulting	O
in	O
a	O
general	O
consensus	O
emerging	O
from	O
multiple	O
different	O
nodes	O
.	O
</s>
<s>
This	O
also	O
makes	O
the	O
process	O
of	O
"	O
forking	O
"	O
easy	O
,	O
as	O
all	O
that	O
is	O
required	O
is	O
one	O
contributor	O
stop	O
accepting	O
pull	O
requests	O
from	O
other	O
contributors	O
and	O
letting	O
the	O
codebases	B-General_Concept
gradually	O
grow	O
apart	O
.	O
</s>
<s>
While	O
distributed	B-Protocol
version	I-Protocol
control	I-Protocol
systems	I-Protocol
make	O
it	O
easy	O
for	O
new	O
developers	O
to	O
"	O
clone	O
"	O
a	O
copy	O
of	O
any	O
other	O
contributor	O
's	O
repository	O
,	O
in	O
a	O
central	O
model	O
,	O
new	O
developers	O
always	O
clone	O
the	O
central	O
repository	O
to	O
create	O
identical	O
local	O
copies	O
of	O
the	O
code	B-General_Concept
base	I-General_Concept
.	O
</s>
<s>
Organizations	O
utilizing	O
this	O
centralize	O
pattern	O
often	O
choose	O
to	O
host	O
the	O
central	O
repository	O
on	O
a	O
third	O
party	O
service	O
like	O
GitHub	B-Application
,	O
which	O
offers	O
not	O
only	O
more	O
reliable	O
uptime	B-Device
than	O
self-hosted	O
repositories	O
,	O
but	O
can	O
also	O
add	O
centralized	O
features	O
like	O
issue	B-Application
trackers	I-Application
and	O
continuous	O
integration	O
.	O
</s>
<s>
Contributions	O
to	O
a	O
source	O
code	O
repository	O
that	O
uses	O
a	O
distributed	B-Protocol
version	I-Protocol
control	I-Protocol
system	I-Protocol
are	O
commonly	O
made	O
by	O
means	O
of	O
a	O
pull	O
request	O
,	O
also	O
known	O
as	O
a	O
merge	B-General_Concept
request	O
.	O
</s>
<s>
The	O
maintainer	O
has	O
to	O
merge	B-General_Concept
the	O
pull	O
request	O
if	O
the	O
contribution	O
should	O
become	O
part	O
of	O
the	O
source	O
base	O
.	O
</s>
<s>
Therefore	O
,	O
some	O
projects	O
contain	O
a	O
special	O
branch	O
for	O
merging	B-General_Concept
untested	O
pull	O
requests	O
.	O
</s>
<s>
The	O
first	O
open-source	B-Application
DVCS	O
systems	O
included	O
Arch	B-Protocol
,	O
Monotone	B-Application
,	O
and	O
Darcs	B-Protocol
.	O
</s>
<s>
However	O
,	O
open	B-Application
source	I-Application
DVCSs	O
were	O
never	O
very	O
popular	O
until	O
the	O
release	O
of	O
Git	B-Application
and	O
Mercurial	B-Protocol
.	O
</s>
<s>
BitKeeper	B-Protocol
was	O
used	O
in	O
the	O
development	O
of	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
from	O
2002	O
to	O
2005	O
.	O
</s>
<s>
The	O
development	O
of	O
Git	B-Application
,	O
now	O
the	O
world	O
's	O
most	O
popular	O
version	B-Architecture
control	I-Architecture
system	I-Architecture
,	O
was	O
prompted	O
by	O
the	O
decision	O
of	O
the	O
company	O
that	O
made	O
BitKeeper	B-Protocol
to	O
rescind	O
the	O
free	O
license	O
that	O
Linus	O
Torvalds	O
and	O
some	O
other	O
Linux	B-Operating_System
kernel	I-Operating_System
developers	O
had	O
previously	O
taken	O
advantage	O
of	O
.	O
</s>
