<s>
Bitcoin	B-Protocol
forks	I-Protocol
are	O
defined	O
variantly	O
as	O
changes	O
in	O
the	O
protocol	O
of	O
the	O
bitcoin	B-General_Concept
network	I-General_Concept
or	O
as	O
the	O
situations	O
that	O
occur	O
"	O
when	O
two	O
or	O
more	O
blocks	O
have	O
the	O
same	O
block	O
height	O
"	O
.	O
</s>
<s>
A	O
fork	B-Application
influences	O
the	O
validity	O
of	O
the	O
rules	O
.	O
</s>
<s>
Forks	B-Application
are	O
typically	O
conducted	O
in	O
order	O
to	O
add	O
new	O
features	B-Architecture
to	O
a	O
blockchain	O
,	O
to	O
reverse	O
the	O
effects	O
of	O
hacking	O
or	O
catastrophic	O
bugs	B-Error_Name
.	O
</s>
<s>
Forks	B-Application
require	O
consensus	O
to	O
be	O
resolved	O
or	O
else	O
a	O
permanent	O
split	O
emerges	O
.	O
</s>
<s>
The	O
following	O
are	O
forks	B-Application
of	O
the	O
software	B-Protocol
client	I-Protocol
for	O
the	O
bitcoin	B-General_Concept
network	I-General_Concept
:	O
</s>
<s>
Bitcoin	B-Protocol
XT	I-Protocol
A	O
fork	B-Application
initiated	O
by	O
Mike	B-Application
Hearn	I-Application
.	O
</s>
<s>
The	O
current	O
reference	O
implementation	O
for	O
bitcoin	B-Protocol
contains	O
a	O
computational	O
bottleneck	O
.	O
</s>
<s>
The	O
actual	O
fork	B-Application
was	O
preceded	O
by	O
Mike	B-Application
Hearn	I-Application
publishing	O
a	O
Bitcoin	B-Protocol
Improvement	O
Proposal	O
(	O
BIP	O
64	O
)	O
on	O
June	O
10	O
,	O
2014	O
,	O
calling	O
for	O
the	O
addition	O
of	O
"	O
a	O
small	O
P2P	O
protocol	O
extension	O
that	O
performs	O
UTXO	B-Protocol
lookups	O
given	O
a	O
set	O
of	O
outpoints.	O
"	O
</s>
<s>
It	O
achieved	O
significant	O
attention	O
within	O
the	O
bitcoin	B-Protocol
community	O
in	O
mid-2015	O
amid	O
a	O
contentious	O
debate	O
among	O
core	O
developers	O
over	O
increasing	O
the	O
block	O
size	O
cap	O
.	O
</s>
<s>
The	O
changes	O
would	O
activate	O
a	O
fork	B-Application
allowing	O
eight	O
MB	O
blocks	O
(	O
doubling	O
in	O
size	O
every	O
two	O
years	O
)	O
once	O
75%	O
of	O
a	O
stretch	O
of	O
1,000	O
mined	O
blocks	O
is	O
achieved	O
after	O
the	O
beginning	O
of	O
2016	O
.	O
</s>
<s>
On	O
August	O
6	O
,	O
2015	O
Andresen	O
's	O
BIP101	O
proposal	O
was	O
merged	O
into	O
the	O
XT	O
codebase	B-General_Concept
.	O
</s>
<s>
Bip	O
101	O
was	O
reverted	O
and	O
the	O
2-MB	O
block	O
size	O
bump	O
of	O
Bitcoin	B-Protocol
Classic	I-Protocol
was	O
applied	O
instead	O
.	O
</s>
<s>
The	O
Guardian	O
wrote	O
that	O
"	O
bitcoin	B-Protocol
is	O
facing	O
civil	O
war	O
"	O
.	O
</s>
<s>
Wired	O
wrote	O
that	O
"	O
Bitcoin	B-Protocol
XT	I-Protocol
exposes	O
the	O
extremely	O
social	O
—	O
extremely	O
democratic	O
—	O
underpinnings	O
of	O
the	O
open	O
source	O
idea	O
,	O
an	O
approach	O
that	O
makes	O
open	O
source	O
so	O
much	O
more	O
powerful	O
than	O
technology	O
controlled	O
by	O
any	O
one	O
person	O
or	O
organization.	O
"	O
</s>
<s>
On	O
August	O
25	O
,	O
2017	O
,	O
Bitcoin	B-Protocol
XT	I-Protocol
published	O
Release	O
G	O
,	O
which	O
was	O
a	O
Bitcoin	B-Protocol
Cash	I-Protocol
client	O
by	O
default	O
.	O
</s>
<s>
Subsequently	O
,	O
Release	O
H	O
was	O
published	O
,	O
which	O
supported	O
the	O
November	O
2017	O
Bitcoin	B-Protocol
Cash	I-Protocol
protocol	O
upgrade	O
,	O
followed	O
by	O
Release	O
I	O
,	O
which	O
supported	O
the	O
May	O
2018	O
Bitcoin	B-Protocol
Cash	I-Protocol
protocol	O
upgrade	O
.	O
</s>
<s>
Bitcoin	B-Protocol
Classic	I-Protocol
In	O
its	O
first	O
8	O
months	O
,	O
Bitcoin	B-Protocol
Classic	I-Protocol
promoted	O
a	O
single	O
increase	O
of	O
the	O
maximum	O
block	O
size	O
from	O
one	O
megabyte	O
to	O
two	O
megabytes	O
.	O
</s>
<s>
All	O
three	O
software	B-Protocol
clients	I-Protocol
attempt	O
to	O
increase	O
transaction	O
capacity	O
of	O
the	O
network	O
.	O
</s>
<s>
Hard	O
forks	B-Application
splitting	O
bitcoin	B-Protocol
(	O
aka	O
"	O
split	O
coins	O
"	O
)	O
are	O
created	O
via	O
changes	O
of	O
the	O
blockchain	O
rules	O
and	O
sharing	O
a	O
transaction	O
history	O
with	O
bitcoin	B-Protocol
up	O
to	O
a	O
certain	O
time	O
and	O
date	O
.	O
</s>
<s>
The	O
first	O
hard	O
fork	B-Application
splitting	O
bitcoin	B-Protocol
happened	O
on	O
1	O
August	O
2017	O
,	O
resulting	O
in	O
the	O
creation	O
of	O
Bitcoin	B-Protocol
Cash	I-Protocol
.	O
</s>
<s>
The	O
following	O
is	O
a	O
list	O
of	O
notable	O
hard	O
forks	B-Application
splitting	O
bitcoin	B-Protocol
by	O
date	O
and/or	O
block	O
:	O
</s>
<s>
Bitcoin	B-Protocol
SV	O
:	O
Forked	O
at	O
block	O
556766	O
,	O
15	O
November	O
2018	O
,	O
for	O
each	O
Bitcoin	B-Protocol
Cash	I-Protocol
(	O
BCH	O
)	O
,	O
an	O
owner	O
got	O
1	O
Bitcoin	B-Protocol
SV	O
(	O
BSV	O
)	O
.	O
</s>
<s>
eCash	O
:	O
Forked	O
at	O
block	O
661648	O
,	O
15	O
November	O
2020	O
,	O
for	O
each	O
Bitcoin	B-Protocol
Cash	I-Protocol
(	O
BCH	O
)	O
,	O
an	O
owner	O
got	O
1,000,000	O
eCash	O
(	O
XEC	O
)	O
.	O
</s>
<s>
The	O
fork	B-Application
fixing	O
the	O
value	O
overflow	O
incident	O
was	O
controversial	O
because	O
it	O
was	O
announced	O
after	O
the	O
exploit	O
was	O
mined	O
.	O
</s>
<s>
Taproot	O
is	O
an	O
agreed	O
soft	O
fork	B-Application
in	O
the	O
transaction	O
format	O
.	O
</s>
<s>
The	O
fork	B-Application
adds	O
support	O
for	O
Schnorr	B-Algorithm
signatures	I-Algorithm
,	O
and	O
improves	O
functionality	O
of	O
smart	B-Application
contracts	I-Application
and	O
the	O
Lightning	B-Protocol
Network	I-Protocol
.	O
</s>
<s>
The	O
fork	B-Application
was	O
installed	O
in	O
November	O
2021	O
.	O
</s>
<s>
The	O
upgrade	O
adds	O
privacy	O
features	B-Architecture
.	O
</s>
<s>
Taproot	O
includes	O
Bitcoin	B-Protocol
Improvement	O
Proposal	O
numbers	O
BIP340	O
,	O
BIP341	O
,	O
BIP342	O
.	O
</s>
<s>
Reduced	O
transaction	O
costs	O
:	O
The	O
data	O
size	O
of	O
complex	O
Bitcoin	B-Protocol
transactions	O
is	O
reduced	O
,	O
which	O
leads	O
to	O
lower	O
transaction	O
fees	O
.	O
</s>
<s>
Support	O
for	O
more	O
complicated	O
conditions	O
for	O
a	O
transaction	O
via	O
Schnorr	B-Algorithm
signatures	I-Algorithm
.	O
</s>
<s>
Benefits	O
for	O
the	O
Lightning	B-Protocol
Network	I-Protocol
:	O
More	O
flexibility	O
,	O
privacy	O
enhancement	O
,	O
lower	O
costs	O
.	O
</s>
<s>
Two	O
hard	O
forks	B-Application
were	O
created	O
by	O
"	O
protocol	O
change	O
"	O
definition	O
:	O
</s>
<s>
CVE-2018-17144	O
(	O
Bitcoin	B-Protocol
0.15	O
allowed	O
double	O
spending	O
certain	O
inputs	O
in	O
the	O
same	O
block	O
.	O
</s>
