<s>
Concurrent	B-Application
Versions	I-Application
System	I-Application
(	O
CVS	B-Application
,	O
also	O
known	O
as	O
the	O
Concurrent	B-Application
Versioning	I-Application
System	I-Application
)	O
is	O
a	O
revision	B-Architecture
control	I-Architecture
system	I-Architecture
originally	O
developed	O
by	O
Dick	O
Grune	O
in	O
July	O
1986	O
.	O
</s>
<s>
CVS	B-Application
operates	O
as	O
a	O
front	B-Architecture
end	I-Architecture
to	O
RCS	B-Architecture
,	O
an	O
earlier	O
system	O
which	O
operates	O
on	O
single	O
files	O
.	O
</s>
<s>
It	O
expands	O
upon	O
RCS	B-Architecture
by	O
adding	O
support	O
for	O
repository-level	O
change	O
tracking	O
,	O
and	O
a	O
client-server	B-Operating_System
model	I-Operating_System
.	O
</s>
<s>
Released	O
under	O
the	O
terms	O
of	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
,	O
CVS	B-Application
is	O
free	B-Application
software	I-Application
.	O
</s>
<s>
CVS	B-Application
operates	O
as	O
a	O
front	B-Architecture
end	I-Architecture
to	O
Revision	B-Architecture
Control	I-Architecture
System	I-Architecture
(	O
RCS	B-Architecture
)	O
,	O
an	O
older	O
version	B-Architecture
control	I-Architecture
system	I-Architecture
that	O
manages	O
individual	O
files	O
but	O
not	O
whole	O
projects	O
.	O
</s>
<s>
It	O
expands	O
upon	O
RCS	B-Architecture
by	O
adding	O
support	O
for	O
repository-level	O
change	O
tracking	O
,	O
and	O
a	O
client-server	B-Operating_System
model	I-Operating_System
.	O
</s>
<s>
Files	O
are	O
tracked	O
using	O
the	O
same	O
history	O
format	O
as	O
in	O
RCS	B-Architecture
,	O
with	O
a	O
hidden	B-Application
directory	I-Application
containing	O
a	O
corresponding	O
history	O
file	O
for	O
each	O
file	O
in	O
the	O
repository	B-Protocol
.	O
</s>
<s>
CVS	B-Application
uses	O
delta	B-Algorithm
compression	I-Algorithm
for	O
efficient	O
storage	O
of	O
different	O
versions	O
of	O
the	O
same	O
file	O
.	O
</s>
<s>
On	O
the	O
other	O
hand	O
,	O
when	O
CVS	B-Application
is	O
told	O
to	O
store	O
a	O
file	O
as	O
binary	O
,	O
it	O
will	O
keep	O
each	O
individual	O
version	O
on	O
the	O
server	O
.	O
</s>
<s>
CVS	B-Application
excludes	O
symbolic	B-Application
links	I-Application
because	O
when	O
they	O
are	O
stored	O
in	O
a	O
version	B-Architecture
control	I-Architecture
system	I-Architecture
they	O
can	O
pose	O
a	O
security	O
risk	O
.	O
</s>
<s>
For	O
instance	O
,	O
a	O
symbolic	B-Application
link	I-Application
to	O
a	O
sensitive	O
file	O
can	O
be	O
stored	O
in	O
the	O
repository	B-Protocol
,	O
making	O
the	O
sensitive	O
file	O
accessible	O
even	O
when	O
it	O
is	O
not	O
checked	O
in	O
.	O
</s>
<s>
In	O
place	O
of	O
symbolic	B-Application
links	I-Application
,	O
scripts	O
that	O
require	O
certain	O
privileges	O
and	O
conscious	O
intervention	O
to	O
execute	O
may	O
be	O
checked	O
into	O
CVS	B-Application
.	O
</s>
<s>
CVS	B-Application
labels	O
a	O
single	O
project	O
(	O
set	O
of	O
related	O
files	O
)	O
that	O
it	O
manages	O
as	O
a	O
module	B-Architecture
.	O
</s>
<s>
A	O
CVS	B-Application
server	O
stores	O
the	O
modules	B-Architecture
it	O
manages	O
in	O
its	O
repository	B-Protocol
.	O
</s>
<s>
Programmers	O
acquire	O
copies	O
of	O
modules	B-Architecture
by	O
checking	O
out	O
.	O
</s>
<s>
Changes	O
to	O
the	O
working	O
copy	O
are	O
reflected	O
in	O
the	O
repository	B-Protocol
by	O
committing	B-Language
them	O
.	O
</s>
<s>
To	O
update	O
is	O
to	O
acquire	O
or	O
merge	B-General_Concept
the	O
changes	O
in	O
the	O
repository	B-Protocol
with	O
the	O
working	O
copy	O
.	O
</s>
<s>
CVS	B-Application
uses	O
a	O
client	B-Operating_System
–	I-Operating_System
server	I-Operating_System
architecture	I-Operating_System
:	O
a	O
server	O
stores	O
the	O
current	O
version(s )	O
of	O
a	O
project	O
and	O
its	O
history	O
,	O
and	O
clients	O
connect	O
to	O
the	O
server	O
in	O
order	O
to	O
"	O
check	O
out	O
"	O
a	O
complete	O
copy	O
of	O
the	O
project	O
,	O
work	O
on	O
this	O
copy	O
and	O
then	O
later	O
"	O
check	O
in	O
"	O
their	O
changes	O
.	O
</s>
<s>
CVS	B-Application
servers	O
can	O
allow	O
"	O
anonymous	O
read	O
access	O
"	O
,	O
wherein	O
clients	O
may	O
check	O
out	O
and	O
compare	O
versions	O
with	O
either	O
a	O
blank	O
or	O
simple	O
published	O
password	O
(	O
e.g.	O
,	O
"	O
anoncvs	O
"	O
)	O
;	O
only	O
the	O
check-in	O
of	O
changes	O
requires	O
a	O
personal	O
account	O
and	O
password	O
in	O
these	O
scenarios	O
.	O
</s>
<s>
This	O
task	O
is	O
mostly	O
handled	O
automatically	O
by	O
the	O
CVS	B-Application
client	O
,	O
requiring	O
manual	O
intervention	O
only	O
when	O
an	O
edit	B-Operating_System
conflict	I-Operating_System
arises	O
between	O
a	O
checked-in	O
modification	O
and	O
the	O
yet-unchecked	O
local	O
version	O
of	O
a	O
file	O
.	O
</s>
<s>
CVS	B-Application
can	O
also	O
run	O
external	O
,	O
user-specified	O
log	O
processing	O
scripts	O
following	O
each	O
commit	O
.	O
</s>
<s>
These	O
scripts	O
are	O
installed	O
by	O
an	O
entry	O
in	O
CVS	B-Application
's	O
loginfo	O
file	O
,	O
which	O
can	O
trigger	O
email	O
notification	O
or	O
convert	O
the	O
log	O
data	O
into	O
a	O
Web-based	O
format	O
.	O
</s>
<s>
CVS	B-Application
can	O
also	O
maintain	O
different	O
"	O
branches	O
"	O
of	O
a	O
project	O
.	O
</s>
<s>
CVS	B-Application
assumes	O
that	O
the	O
majority	O
of	O
work	O
takes	O
place	O
on	O
the	O
trunk	O
,	O
and	O
that	O
branches	O
should	O
generally	O
be	O
short-lived	O
or	O
historical	O
.	O
</s>
<s>
The	O
server	O
software	O
normally	O
runs	O
on	O
Unix	B-Application
(	O
although	O
at	O
least	O
the	O
CVSNT	B-Protocol
server	O
also	O
supports	O
various	O
flavors	O
of	O
Microsoft	B-Application
Windows	I-Application
)	O
,	O
while	O
CVS	B-Application
clients	O
may	O
run	O
on	O
any	O
major	O
operating	B-General_Concept
system	I-General_Concept
platform	O
.	O
</s>
<s>
The	O
code	O
that	O
eventually	O
evolved	O
into	O
the	O
current	O
version	O
of	O
CVS	B-Application
started	O
with	O
Brian	O
Berliner	O
in	O
April	O
1989	O
,	O
with	O
later	O
input	O
from	O
Jeff	O
Polk	O
and	O
many	O
other	O
contributors	O
.	O
</s>
<s>
Brian	O
Berliner	O
wrote	O
a	O
paper	O
introducing	O
his	O
improvements	O
to	O
the	O
CVS	B-Application
program	O
—	O
which	O
describes	O
how	O
the	O
tool	O
was	O
extended	O
and	O
used	O
internally	O
by	O
Prisma	O
,	O
a	O
third-party	O
developer	O
working	O
on	O
the	O
SunOS	O
kernel	O
,	O
and	O
was	O
released	O
for	O
the	O
benefit	O
of	O
the	O
community	O
under	O
the	O
GPL	B-License
.	O
</s>
<s>
On	O
November	O
19	O
,	O
1990	O
,	O
CVS	B-Application
version	O
1.0	O
was	O
submitted	O
to	O
the	B-Operating_System
Free	I-Operating_System
Software	I-Operating_System
Foundation	I-Operating_System
for	O
development	O
and	O
distribution	O
.	O
</s>
<s>
Over	O
time	O
,	O
developers	O
have	O
created	O
new	O
version	B-Architecture
control	I-Architecture
systems	I-Architecture
based	O
on	O
CVS	B-Application
in	O
order	O
to	O
add	O
features	O
,	O
alter	O
the	O
operational	O
model	O
,	O
and	O
improve	O
developers	O
 '	O
productivity	O
.	O
</s>
<s>
CVS	B-Application
replacement	O
projects	O
include	O
CVSNT	B-Protocol
and	O
Subversion	B-Application
.	O
</s>
