<s>
Hercules	B-Application
is	O
a	O
computer	B-Application
emulator	I-Application
allowing	O
software	O
written	O
for	O
IBM	B-Device
mainframe	I-Device
computers	O
(	O
System/370	B-Device
,	O
System/390	B-Device
,	O
and	O
zSeries/System	B-Device
z	I-Device
)	O
and	O
for	O
plug	B-Device
compatible	I-Device
mainframes	O
(	O
such	O
as	O
Amdahl	O
machines	O
)	O
to	O
run	O
on	O
other	O
types	O
of	O
computer	O
hardware	O
,	O
notably	O
on	O
low-cost	O
personal	B-Device
computers	I-Device
.	O
</s>
<s>
Hercules	B-Application
runs	O
under	O
multiple	O
parent	O
operating	B-General_Concept
systems	I-General_Concept
including	O
Linux	B-Application
,	O
Microsoft	B-Application
Windows	I-Application
,	O
FreeBSD	B-Operating_System
,	O
NetBSD	B-Device
,	O
Solaris	B-Application
,	O
and	O
macOS	B-Application
and	O
is	O
released	O
under	O
the	O
open	B-Application
source	I-Application
software	I-Application
license	O
QPL	B-Language
.	O
</s>
<s>
It	O
is	O
analogous	O
to	O
Bochs	B-Language
and	O
QEMU	B-Application
in	O
that	O
it	O
emulates	B-Application
CPU	B-General_Concept
instructions	O
and	O
select	O
peripheral	O
devices	O
only	O
.	O
</s>
<s>
A	O
vendor	O
(	O
or	O
distributor	O
)	O
must	O
still	O
provide	O
an	O
operating	B-General_Concept
system	I-General_Concept
,	O
and	O
the	O
user	O
must	O
install	O
it	O
.	O
</s>
<s>
Hercules	B-Application
was	O
the	O
first	O
mainframe	O
emulator	B-Application
to	O
incorporate	O
64-bit	O
z/Architecture	B-Device
support	O
.	O
</s>
<s>
The	O
emulator	B-Application
is	O
written	O
almost	O
entirely	O
in	O
C	B-Language
.	O
Its	O
developers	O
ruled	O
out	O
using	O
machine-specific	O
assembly	B-Language
code	I-Language
to	O
avoid	O
problems	O
with	O
portability	O
even	O
though	O
such	O
code	O
could	O
significantly	O
improve	O
performance	O
.	O
</s>
<s>
There	O
are	O
two	O
exceptions	O
:	O
Hercules	B-Application
uses	O
hardware	O
assists	O
to	O
provide	O
inter-processor	O
consistency	O
when	O
emulating	B-Application
multiple	O
CPUs	O
on	O
SMP	O
host	O
systems	O
,	O
and	O
Hercules	B-Application
uses	O
assembler	B-Language
assists	O
to	O
convert	O
between	O
little-endian	O
and	O
big-endian	O
data	O
on	O
platforms	O
where	O
the	O
operating	B-General_Concept
system	I-General_Concept
provides	O
such	O
services	O
and	O
on	O
x86/x86	O
-64	O
processors	O
.	O
</s>
<s>
Hercules	B-Application
is	O
technically	O
compatible	O
with	O
all	O
IBM	B-Device
mainframe	I-Device
operating	B-General_Concept
systems	I-General_Concept
,	O
even	O
older	O
versions	O
which	O
no	O
longer	O
run	O
on	O
newer	O
mainframes	O
.	O
</s>
<s>
However	O
,	O
many	O
mainframe	O
operating	B-General_Concept
systems	I-General_Concept
require	O
vendor	O
licenses	O
to	O
run	O
legally	O
.	O
</s>
<s>
Newer	O
licensed	O
operating	B-General_Concept
systems	I-General_Concept
,	O
such	O
as	O
OS/390	B-Application
,	O
z/OS	B-Application
,	O
VSE/ESA	O
,	O
z/VSE	B-Application
,	O
VM/ESA	B-Application
,	O
z/VM	B-Application
,	O
TPF/ESA	B-Operating_System
,	O
and	O
z/TPF	B-Operating_System
are	O
technically	O
compatible	O
but	O
cannot	O
legally	O
run	O
on	O
the	O
Hercules	B-Application
emulator	I-Application
except	O
in	O
very	O
limited	O
circumstances	O
,	O
and	O
they	O
must	O
always	O
be	O
licensed	O
from	O
IBM	O
.	O
</s>
<s>
IBM	O
's	O
Coupling	B-Device
Facility	I-Device
control	O
code	O
,	O
which	O
enables	O
Parallel	B-Operating_System
Sysplex	I-Operating_System
,	O
and	O
UTS	B-Operating_System
also	O
require	O
licenses	O
to	O
run	O
.	O
</s>
<s>
Operating	B-General_Concept
systems	I-General_Concept
which	O
may	O
legally	O
be	O
run	O
,	O
without	O
license	O
costs	O
,	O
on	O
Hercules	B-Application
include	O
:	O
</s>
<s>
Older	O
IBM	O
operating	B-General_Concept
systems	I-General_Concept
including	O
OS/360	B-Application
,	O
DOS/360	O
,	O
DOS/VS	B-Application
,	O
MVS	B-Application
,	O
VM/370	B-Application
,	O
and	O
TSS/370	B-Application
which	O
are	O
either	O
public	O
domain	O
or	O
"	O
copyrighted	O
software	O
provided	O
without	O
charge.	O
"	O
</s>
<s>
The	O
MUSIC/SP	B-Application
operating	B-General_Concept
system	I-General_Concept
may	O
be	O
available	O
for	O
educational	O
and	O
demonstration	O
purposes	O
upon	O
request	O
to	O
its	O
copyright	O
holder	O
,	O
McGill	O
University	O
.	O
</s>
<s>
Some	O
of	O
MUSIC/SP	B-Application
'	O
s	O
features	O
,	O
notably	O
networking	O
,	O
require	O
z/VM	B-Application
(	O
and	O
thus	O
an	O
IBM	O
license	O
)	O
.	O
</s>
<s>
However	O
,	O
a	O
complete	O
demonstration	O
version	O
of	O
MUSIC/SP	B-Application
,	O
packaged	O
with	O
the	O
alternative	O
Sim390	O
mainframe	O
emulator	B-Application
,	O
is	O
available	O
.	O
</s>
<s>
The	O
Michigan	B-Application
Terminal	I-Application
System	I-Application
(	O
MTS	O
)	O
version	O
6.0A	O
has	O
been	O
tailored	O
to	O
run	O
under	O
Hercules	B-Application
.	O
</s>
<s>
There	O
is	O
no	O
known	O
legal	O
restriction	O
to	O
running	O
open-source	B-Application
operating	B-General_Concept
systems	I-General_Concept
Linux	B-Application
on	I-Application
IBM	I-Application
Z	I-Application
and	O
OpenSolaris	B-Application
for	I-Application
System	I-Application
z	I-Application
on	O
the	O
Hercules	B-Application
emulator	I-Application
.	O
</s>
<s>
They	O
run	O
well	O
on	O
Hercules	B-Application
,	O
and	O
many	O
Linux	B-Application
on	I-Application
IBM	I-Application
Z	I-Application
developers	O
do	O
their	O
work	O
using	O
Hercules	B-Application
.	O
</s>
<s>
Several	O
distributors	O
provide	O
64-bit	O
z/Architecture	B-Device
versions	O
of	O
Linux	B-Application
,	O
and	O
some	O
also	O
provide	O
ESA/390	O
-compatible	O
versions	O
.	O
</s>
<s>
Mainframe	B-Application
Linux	I-Application
distributions	O
include	O
SUSE	O
Linux	B-Application
Enterprise	O
Server	O
,	O
Red	O
Hat	O
Enterprise	O
Linux	B-Application
,	O
Debian	O
,	O
CentOS	O
,	O
and	O
Slackware	B-Application
.	O
</s>
<s>
Sine	O
Nomine	O
Associates	O
brought	O
OpenSolaris	O
to	O
System	B-Device
z	I-Device
,	O
relying	O
on	O
features	O
provided	O
by	O
z/VM	B-Application
.	O
</s>
<s>
Emulation	B-Application
of	O
those	O
specific	O
z/VM	B-Application
features	O
for	O
OpenSolaris	O
is	O
included	O
starting	O
with	O
Hercules	B-Application
Version	O
3.07	O
.	O
</s>
<s>
Certain	O
unencumbered	O
editors	O
and	O
utilities	O
which	O
can	O
run	O
on	O
a	O
mainframe	O
without	O
a	O
parent	O
operating	B-General_Concept
system	I-General_Concept
may	O
be	O
available	O
to	O
run	O
on	O
Hercules	B-Application
as	O
well	O
.	O
</s>
<s>
Hercules	B-Application
can	O
be	O
used	O
as	O
a	O
development	O
environment	O
to	O
verify	O
that	O
code	O
is	O
portable	O
(	O
across	O
Linux	B-Application
processor	O
architectures	O
,	O
for	O
example	O
)	O
,	O
supports	O
symmetric	B-Operating_System
multiprocessing	I-Operating_System
(	O
SMP	O
)	O
,	O
and	O
is	O
64-bit	O
"	O
clean.	O
"	O
</s>
<s>
There	O
is	O
also	O
a	O
large	O
community	O
of	O
current	O
and	O
former	O
mainframe	O
operators	O
and	O
programmers	O
,	O
as	O
well	O
as	O
those	O
with	O
no	O
prior	O
experience	O
,	O
who	O
use	O
Hercules	B-Application
and	O
the	O
public	O
domain	O
IBM	O
operating	B-General_Concept
systems	I-General_Concept
as	O
a	O
hobby	O
and	O
for	O
learning	O
purposes	O
.	O
</s>
<s>
Most	O
of	O
the	O
skills	O
acquired	O
when	O
exploring	O
classic	O
IBM	B-Device
mainframe	I-Device
operating	B-General_Concept
system	I-General_Concept
versions	O
are	O
still	O
relevant	O
when	O
transitioning	O
to	O
licensed	O
IBM	O
machines	O
running	O
the	O
latest	O
versions	O
.	O
</s>
<s>
The	O
open	B-Application
source	I-Application
nature	O
of	O
Hercules	B-Application
means	O
that	O
anyone	O
can	O
produce	O
their	O
own	O
customized	O
version	O
of	O
the	O
emulator	B-Application
.	O
</s>
<s>
For	O
example	O
,	O
a	O
group	O
of	O
developers	O
independent	O
of	O
the	O
Hercules	B-Application
project	O
implemented	O
a	O
hybrid	O
mainframe	O
architecture	O
which	O
they	O
dubbed	O
"	O
S/380	O
"	O
using	O
modifications	O
to	O
both	O
Hercules	B-Application
and	O
to	O
freely	O
available	O
classic	O
versions	O
of	O
MVS	B-Application
(	O
and	O
later	O
VM	B-Application
and	O
DOS/VS	B-Application
)	O
,	O
enhancing	O
the	O
operating	B-General_Concept
systems	I-General_Concept
with	O
some	O
degree	O
of	O
31-bit	O
(	O
and	O
as	O
of	O
2016	O
,	O
64-bit	O
)	O
binary	O
compatibility	O
with	O
later	O
operating	B-General_Concept
system	I-General_Concept
versions	O
(	O
and	O
as	O
of	O
2018	O
,	O
32-bit	O
is	O
also	O
supported	O
)	O
.	O
</s>
<s>
It	O
is	O
difficult	O
to	O
determine	O
exactly	O
how	O
Hercules	B-Application
emulation	B-Application
performance	O
corresponds	O
to	O
real	O
mainframe	O
hardware	O
,	O
but	O
the	O
performance	O
characteristics	O
are	O
understandably	O
quite	O
different	O
.	O
</s>
<s>
This	O
is	O
partially	O
due	O
to	O
the	O
difficulty	O
of	O
comparing	O
real	O
mainframe	O
hardware	O
to	O
other	O
PCs	B-Device
and	O
servers	O
as	O
well	O
as	O
the	O
lack	O
of	O
concrete	O
,	O
controlled	O
performance	O
comparisons	O
.	O
</s>
<s>
Performance	O
comparisons	O
are	O
likely	O
legally	O
impossible	O
for	O
licensed	O
IBM	O
operating	B-General_Concept
systems	I-General_Concept
,	O
and	O
those	O
operating	B-General_Concept
systems	I-General_Concept
are	O
quite	O
different	O
from	O
other	O
operating	B-General_Concept
systems	I-General_Concept
,	O
such	O
as	O
Linux	B-Application
.	O
</s>
<s>
Hercules	B-Application
expresses	O
its	O
processing	O
performance	O
in	O
MIPS	O
.	O
</s>
<s>
Due	O
to	O
the	O
age	O
of	O
the	O
earlier	O
System/360	O
and	O
System/370	B-Device
hardware	O
,	O
it	O
is	O
a	O
relatively	O
safe	O
assumption	O
that	O
Hercules	B-Application
will	O
outperform	O
them	O
when	O
running	O
on	O
moderately	O
powerful	O
hardware	O
,	O
despite	O
the	O
considerable	O
overhead	O
of	O
emulating	B-Application
a	O
computer	O
architecture	O
in	O
software	O
.	O
</s>
<s>
However	O
,	O
newer	O
,	O
partially	O
or	O
fully	O
configured	O
System	B-Device
z	I-Device
machines	O
outperform	O
Hercules	B-Application
by	O
a	O
wide	O
margin	O
.	O
</s>
<s>
A	O
relatively	O
fast	O
dual	O
processor	O
X86	B-Operating_System
machine	O
running	O
Hercules	B-Application
is	O
capable	O
of	O
sustaining	O
about	O
50	O
to	O
60	O
MIPS	O
for	O
code	O
that	O
utilizes	O
both	O
processors	O
in	O
a	O
realistic	O
environment	O
,	O
with	O
sustained	O
rates	O
rising	O
to	O
a	O
reported	O
300	O
MIPS	O
on	O
leading-edge	O
(	O
early	O
2009	O
)	O
PC-class	O
systems	O
.	O
</s>
<s>
Hercules	B-Application
can	O
produce	O
peaks	O
of	O
over	O
1200	O
MIPS	O
when	O
running	O
in	O
a	O
tight	O
loop	O
,	O
such	O
as	O
in	O
a	O
synthetic	O
instruction	O
benchmark	O
or	O
with	O
other	O
small	O
,	O
compute-intensive	O
programs	O
.	O
</s>
<s>
Tom	O
Lehmann	O
,	O
co-founder	O
of	O
TurboHercules	B-Application
,	O
wrote	O
:	O
</s>
<s>
Hercules	B-Application
generally	O
outperforms	O
IBM	B-Operating_System
's	I-Operating_System
PC	I-Operating_System
based	I-Operating_System
mainframes	I-Operating_System
from	O
the	O
mid-1990s	O
,	O
which	O
have	O
an	O
advertised	O
peak	O
performance	O
of	O
around	O
29	O
MIPS	O
.	O
</s>
<s>
Compared	O
to	O
the	O
more	O
powerful	O
but	O
still	O
entry-level	O
IBM	O
Multiprise	O
2000	O
and	O
3000	O
mainframes	O
(	O
also	O
from	O
the	O
1990s	O
)	O
,	O
Hercules	B-Application
on	O
typical	O
x86	B-Operating_System
hardware	O
would	O
be	O
considered	O
a	O
mid-range	O
server	O
in	O
performance	O
terms	O
.	O
</s>
<s>
For	O
every	O
mainframe	O
after	O
the	O
9672	O
Generation	O
1	O
,	O
Hercules	B-Application
would	O
generally	O
be	O
the	O
lowest	O
end	O
system	O
.	O
</s>
<s>
For	O
comparison	O
,	O
2010-era	O
high-end	O
IBM	B-Device
zEnterprise	I-Device
196	O
systems	O
can	O
deliver	O
over	O
52,000	O
MIPS	O
per	O
machine	O
,	O
and	O
they	O
have	O
considerable	O
I/O	O
performance	O
advantages	O
.	O
</s>
<s>
With	O
the	O
same	O
number	O
of	O
emulated	B-Application
Sys	O
Z	O
processors	O
,	O
z/PDT	O
is	O
about	O
3	O
times	O
faster	O
than	O
Hercules	B-Application
.	O
</s>
<s>
In	O
2009	O
,	O
Roger	O
Bowler	O
founded	O
TurboHercules	B-Application
SAS	O
,	O
based	O
in	O
France	O
,	O
to	O
commercialize	O
the	O
Hercules	B-Application
technology	O
.	O
</s>
<s>
In	O
July	O
2009	O
,	O
TurboHercules	B-Application
SAS	O
asked	O
IBM	O
to	O
license	O
z/OS	B-Application
to	O
its	O
customers	O
for	O
use	O
on	O
systems	O
sold	O
by	O
TurboHercules	B-Application
.	O
</s>
<s>
In	O
March	O
2010	O
,	O
TurboHercules	B-Application
SAS	O
filed	O
a	O
complaint	O
with	O
European	O
Commission	O
regulators	O
,	O
alleging	O
that	O
IBM	O
infringed	O
EU	O
antitrust	O
rules	O
through	O
its	O
alleged	O
tying	O
of	O
mainframe	O
hardware	O
to	O
its	O
mainframe	O
operating	B-General_Concept
system	I-General_Concept
,	O
and	O
the	O
EC	O
opened	O
a	O
preliminary	O
investigation	O
.	O
</s>
<s>
In	O
November	O
2010	O
,	O
TurboHercules	B-Application
announced	O
that	O
it	O
had	O
received	O
an	O
investment	O
from	O
Microsoft	O
Corporation	O
.	O
</s>
