<s>
Reverse	B-Application
computation	I-Application
is	O
a	O
software	B-Application
application	O
of	O
the	O
concept	O
of	O
reversible	B-Application
computing	I-Application
.	O
</s>
<s>
Because	O
it	O
offers	O
a	O
possible	O
solution	O
to	O
the	O
heat	O
problem	O
faced	O
by	O
chip	O
manufacturers	O
,	O
reversible	B-Application
computing	I-Application
has	O
been	O
extensively	O
studied	O
in	O
the	O
area	O
of	O
computer	O
architecture	O
.	O
</s>
<s>
The	O
promise	O
of	O
reversible	B-Application
computing	I-Application
is	O
that	O
the	O
amount	O
of	O
heat	O
loss	O
for	O
reversible	O
architectures	O
would	O
be	O
minimal	O
for	O
significantly	O
large	O
numbers	O
of	O
transistors	O
.	O
</s>
<s>
The	O
concept	O
of	O
reverse	B-Application
computation	I-Application
is	O
somewhat	O
simpler	O
than	O
reversible	B-Application
computing	I-Application
in	O
that	O
reverse	B-Application
computation	I-Application
is	O
only	O
required	O
to	O
restore	O
the	O
equivalent	O
state	O
of	O
a	O
software	B-Application
application	O
,	O
rather	O
than	O
support	O
the	O
reversibility	O
of	O
the	O
set	O
of	O
all	O
possible	O
instructions	O
.	O
</s>
<s>
Reversible	B-Application
computing	I-Application
concepts	O
have	O
been	O
successfully	O
applied	O
as	O
reverse	B-Application
computation	I-Application
in	O
software	B-Application
application	O
areas	O
such	O
as	O
database	O
design	O
,	O
checkpointing	O
and	O
debugging	O
,	O
and	O
code	O
differentiation	O
.	O
</s>
<s>
The	O
key	O
property	O
that	O
reverse	B-Application
computation	I-Application
exploits	O
is	O
that	O
a	O
majority	O
of	O
the	O
operations	O
that	O
modify	O
the	O
state	O
variables	O
are	O
“	O
constructive	O
”	O
in	O
nature	O
.	O
</s>
<s>
That	O
is	O
,	O
the	O
undo	B-Application
operation	O
for	O
such	O
operations	O
requires	O
no	O
history	O
.	O
</s>
<s>
Only	O
the	O
most	O
current	O
values	O
of	O
the	O
variables	O
are	O
required	O
to	O
undo	B-Application
the	O
operation	O
.	O
</s>
<s>
More	O
complex	O
operations	O
such	O
as	O
circular	B-Algorithm
shift	I-Algorithm
(	O
swap	O
being	O
a	O
special	O
case	O
)	O
,	O
and	O
certain	O
classes	O
of	O
random	O
number	O
generation	O
also	O
belong	O
here	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
the	O
work	O
of	O
Yaun	O
,	O
Carothers	O
,	O
et	O
al.	O
,	O
with	O
large-scale	O
TCP	B-Protocol
simulation	O
,	O
the	O
last-sent	O
time	O
records	O
the	O
time	O
stamp	O
of	O
the	O
last	O
packet	O
forwarded	O
on	O
a	O
router	O
logical	O
process	O
.	O
</s>
<s>
To	O
date	O
,	O
the	O
technique	O
known	O
as	O
Reverse	B-Application
Computation	I-Application
has	O
only	O
been	O
applied	O
in	O
software	B-Application
for	O
optimistically	O
synchronized	O
,	O
parallel	O
discrete	O
event	O
simulation	O
.	O
</s>
<s>
His	O
doctoral	O
thesis	O
focused	O
on	O
reverse	B-Application
computation	I-Application
at	O
the	O
hardware	O
level	O
,	O
but	O
included	O
descriptions	O
of	O
both	O
an	O
instruction	O
set	O
architecture	O
and	O
a	O
high	O
level	O
programming	O
language	O
(	O
R	O
)	O
for	O
a	O
processor	O
based	O
on	O
reverse	B-Application
computation	I-Application
.	O
</s>
<s>
In	O
1998	O
Carothers	O
and	O
Perumalla	O
published	O
a	O
paper	O
for	O
the	O
Principles	O
of	O
Advanced	O
and	O
Distributed	O
Simulation	O
workshop	O
as	O
part	O
of	O
their	O
graduate	O
studies	O
under	O
Richard	O
Fujimoto	O
,	O
introducing	O
technique	O
of	O
Reverse	B-Application
Computation	I-Application
as	O
an	O
alternative	O
rollback	O
mechanism	O
in	O
optimistically	O
synchronized	O
parallel	O
discrete	O
event	O
simulations	O
(	O
Time	O
Warp	O
)	O
.	O
</s>
<s>
Working	O
with	O
graduate	O
students	O
David	O
Bauer	O
and	O
Shawn	O
Pearce	O
,	O
Carothers	O
integrated	O
the	O
Georgia	O
Tech	O
Time	O
Warp	O
design	O
into	O
Rensselaer	O
’s	O
Optimistic	O
Simulation	O
System	O
(	O
ROSS	O
)	O
,	O
which	O
supported	O
only	O
reverse	B-Application
computation	I-Application
as	O
the	O
rollback	O
mechanism	O
.	O
</s>
<s>
Carothers	O
also	O
constructed	O
RC	O
models	O
for	O
BitTorrent	B-Protocol
at	O
General	O
Electric	O
,	O
as	O
well	O
as	O
numerous	O
network	O
protocols	O
with	O
students	O
(	O
BGP4	B-Protocol
,	O
TCP	B-Protocol
Tahoe	O
,	O
Multicast	O
)	O
.	O
</s>
<s>
This	O
was	O
the	O
first	O
implementation	O
of	O
PDES	O
on	O
Blue	O
Gene	O
using	O
reverse	B-Application
computation	I-Application
.	O
</s>
<s>
From	O
1998	O
to	O
2005	O
Bauer	O
performed	O
graduate	O
work	O
at	O
RPI	O
under	O
Carothers	O
,	O
focusing	O
solely	O
on	O
reverse	B-Application
computation	I-Application
.	O
</s>
<s>
He	O
developed	O
the	O
first	O
PDES	O
system	O
solely	O
based	O
on	O
reverse	B-Application
computation	I-Application
,	O
called	O
Rensselaer	O
’s	O
Optimistic	O
Simulation	O
System	O
(	O
ROSS	O
)	O
.	O
</s>
<s>
for	O
combined	O
shared	B-Operating_System
and	O
distributed	B-Operating_System
memory	I-Operating_System
systems	O
.	O
</s>
<s>
For	O
example	O
,	O
creating	O
an	O
LP	O
layering	O
structure	O
to	O
eliminate	O
events	O
being	O
passed	O
between	O
network	O
protocol	O
LPs	O
on	O
the	O
same	O
simulated	O
machine	O
optimizes	O
simulation	O
of	O
TCP/IP	O
network	O
nodes	O
by	O
eliminating	O
zero-offset	O
timestamps	O
between	O
TCP	B-Protocol
and	O
IP	O
protocols	O
.	O
</s>
