<s>
Proof	O
of	O
space	O
(	O
PoS	O
)	O
is	O
a	O
type	O
of	O
consensus	B-Operating_System
algorithm	I-Operating_System
achieved	O
by	O
demonstrating	O
one	O
's	O
legitimate	O
interest	O
in	O
a	O
service	O
(	O
such	O
as	O
sending	O
an	O
email	O
)	O
by	O
allocating	O
a	O
non-trivial	O
amount	O
of	O
memory	B-General_Concept
or	O
disk	B-General_Concept
space	I-General_Concept
to	O
solve	O
a	O
challenge	O
presented	O
by	O
the	O
service	O
provider	O
.	O
</s>
<s>
Proof-of-space	O
is	O
different	O
from	O
memory-hard	O
functions	O
in	O
that	O
the	O
bottleneck	O
is	O
not	O
in	O
the	O
number	O
of	O
memory	B-General_Concept
access	O
events	O
,	O
but	O
in	O
the	O
amount	O
of	O
memory	B-General_Concept
required	O
.	O
</s>
<s>
After	O
the	O
release	O
of	O
Bitcoin	B-Protocol
,	O
alternatives	O
to	O
its	O
PoW	O
mining	O
mechanism	O
were	O
researched	O
,	O
and	O
PoS	O
was	O
studied	O
in	O
the	O
context	O
of	O
cryptocurrencies	O
.	O
</s>
<s>
Proofs	O
of	O
space	O
are	O
seen	O
as	O
a	O
fairer	O
and	O
greener	O
alternative	O
by	O
blockchain	B-Application
enthusiasts	O
due	O
to	O
the	O
general-purpose	O
nature	O
of	O
storage	O
and	O
the	O
lower	O
energy	O
cost	O
required	O
by	O
storage	O
.	O
</s>
<s>
In	O
2014	O
,	O
Signum	O
(	O
formerly	O
Burstcoin	O
)	O
became	O
the	O
first	O
practical	O
implementation	O
of	O
a	O
PoS	O
(	O
initially	O
as	O
proof	O
of	O
capacity	O
)	O
blockchain	B-Application
technology	I-Application
and	O
is	O
still	O
actively	O
developed	O
.	O
</s>
<s>
Cryptocurrencies	O
intended	O
to	O
assign	O
value	O
to	O
store	O
data	O
use	O
some	O
form	O
of	O
this	O
system	O
;	O
examples	O
include	O
Chives	O
,	O
Storj	O
,	O
Sia	O
,	O
Filecoin	B-Protocol
,	O
and	O
Arweave	O
.	O
</s>
<s>
The	O
Proof	O
of	O
Capacity	O
(	O
PoC	O
)	O
consensus	B-Operating_System
algorithm	I-Operating_System
is	O
used	O
in	O
some	O
cryptocurrencies	O
.	O
</s>
<s>
The	O
first	O
implementation	O
of	O
PoST	O
is	O
with	O
the	O
Chia	O
blockchain	B-Application
.	O
</s>
<s>
Proof	O
of	O
capacity	O
consumes	O
disk	B-General_Concept
space	I-General_Concept
rather	O
than	O
computing	O
resources	O
to	O
mine	O
a	O
block	O
.	O
</s>
<s>
Unlike	O
PoW	O
,	O
where	O
the	O
miners	O
keep	O
changing	O
the	O
block	O
header	O
and	O
hash	O
to	O
find	O
the	O
solution	O
,	O
proof	O
of	O
capacity	O
(	O
as	O
implemented	O
by	O
Burstcoin	O
,	O
and	O
developed	O
further	O
by	O
Signum	O
)	O
generates	O
random	O
solutions	O
,	O
also	O
called	O
plots	O
,	O
using	O
the	O
Shabal	O
cryptographic	O
algorithm	O
in	O
advance	O
and	O
stores	O
it	O
on	O
hard	B-Device
drives	I-Device
.	O
</s>
<s>
This	O
stage	O
is	O
called	O
plotting	O
and	O
it	O
may	O
take	O
days	O
or	O
even	O
weeks	O
depending	O
on	O
the	O
storage	B-General_Concept
capacity	I-General_Concept
of	O
the	O
drive	O
.	O
</s>
<s>
Also	O
,	O
Chia	O
's	O
proof-of-time	O
method	O
for	O
plotting	O
has	O
raised	O
concerns	O
over	O
shortened	O
lifespans	O
of	O
solid-state	B-Device
drives	I-Device
due	O
to	O
the	O
intensity	O
of	O
write	O
activity	O
involved	O
in	O
plot	O
generation	O
(	O
typically	O
,	O
plotting	O
occurs	O
on	O
an	O
SSD	B-Device
and	O
then	O
the	O
finished	O
plots	O
are	O
transferred	O
to	O
a	O
hard	B-Device
disk	I-Device
drive	I-Device
for	O
long-term	O
storage	O
)	O
.	O
</s>
<s>
Spacemesh	O
is	O
unique	O
due	O
to	O
its	O
use	O
of	O
a	O
blockmesh	O
,	O
rather	O
than	O
a	O
blockchain	B-Application
.	O
</s>
<s>
While	O
a	O
blockchain	B-Application
is	O
a	O
chain	O
of	O
single	O
blocks	O
,	O
a	O
blockmesh	O
makes	O
use	O
of	O
a	O
directed	O
acyclic	O
graph	O
(	O
DAG	O
)	O
composed	O
of	O
layers	O
,	O
with	O
each	O
layer	O
containing	O
many	O
blocks	O
.	O
</s>
