<s>
Extremely	B-Operating_System
Reliable	I-Operating_System
Operating	I-Operating_System
System	I-Operating_System
(	O
EROS	B-Operating_System
)	O
is	O
an	O
operating	B-General_Concept
system	I-General_Concept
developed	O
starting	O
in	O
1991	O
at	O
the	O
University	O
of	O
Pennsylvania	O
,	O
and	O
then	O
Johns	O
Hopkins	O
University	O
,	O
and	O
The	O
EROS	B-Operating_System
Group	O
,	O
LLC	O
.	O
</s>
<s>
Features	O
include	O
automatic	O
data	O
and	O
process	B-Operating_System
persistence	O
,	O
some	O
preliminary	O
real-time	B-Operating_System
support	O
,	O
and	O
capability-based	O
security	O
.	O
</s>
<s>
EROS	B-Operating_System
is	O
purely	O
a	O
research	O
operating	B-General_Concept
system	I-General_Concept
,	O
and	O
was	O
never	O
deployed	O
in	O
real	O
world	O
use	O
.	O
</s>
<s>
,	O
development	O
stopped	O
in	O
favor	O
of	O
a	O
successor	O
system	O
,	O
CapROS	B-Application
.	O
</s>
<s>
The	O
overriding	O
goal	O
of	O
the	O
EROS	B-Operating_System
system	O
(	O
and	O
its	O
relatives	O
)	O
is	O
to	O
provide	O
strong	O
support	O
at	O
the	O
operating	B-General_Concept
system	I-General_Concept
level	O
for	O
the	O
efficient	O
restructuring	O
of	O
critical	O
applications	O
into	O
small	O
communicating	O
components	O
.	O
</s>
<s>
A	O
protected	O
interface	O
,	O
in	O
this	O
context	O
,	O
is	O
one	O
that	O
is	O
enforced	O
by	O
the	O
lowest	O
level	O
part	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
,	O
the	O
kernel	B-Operating_System
.	O
</s>
<s>
That	O
is	O
the	O
only	O
part	O
of	O
the	O
system	O
that	O
can	O
move	O
information	O
from	O
one	O
process	B-Operating_System
to	O
another	O
.	O
</s>
<s>
In	O
EROS	B-Operating_System
,	O
the	O
kernel-provided	O
mechanism	O
by	O
which	O
one	O
component	O
names	O
and	O
invokes	O
the	O
services	O
of	O
another	O
is	O
a	O
capability	O
,	O
using	O
inter-process	B-Operating_System
communication	I-Operating_System
(	O
IPC	O
)	O
.	O
</s>
<s>
By	O
enforcing	O
capability-protected	O
interfaces	O
,	O
the	O
kernel	B-Operating_System
ensures	O
that	O
all	O
communications	O
to	O
a	O
process	B-Operating_System
arrive	O
via	O
an	O
intentionally	O
exported	O
interface	O
.	O
</s>
<s>
This	O
organizational	O
approach	O
is	O
similar	O
to	O
the	O
programming	O
language	O
concept	O
of	O
object-oriented	B-Language
programming	I-Language
,	O
but	O
occurs	O
at	O
larger	O
granularity	O
and	O
does	O
not	O
include	O
the	O
concept	O
of	O
inheritance	B-Language
.	O
</s>
<s>
The	O
individual	O
components	O
are	O
most	O
naturally	O
structured	O
as	O
event	B-Application
loops	I-Application
.	O
</s>
<s>
Examples	O
of	O
systems	O
that	O
are	O
commonly	O
structured	O
this	O
way	O
include	O
aircraft	O
flight	O
control	O
systems	O
(	O
see	O
also	O
DO-178B	O
Software	O
Considerations	O
in	O
Airborne	O
Systems	O
and	O
Equipment	O
Certification	O
)	O
,	O
and	O
telephone	O
switching	O
systems	O
(	O
see	O
5ESS	B-Device
switch	I-Device
)	O
.	O
</s>
<s>
Event-driven	B-Application
programming	I-Application
is	O
chosen	O
for	O
these	O
systems	O
mainly	O
because	O
of	O
simplicity	O
and	O
robustness	O
,	O
which	O
are	O
essential	O
attributes	O
in	O
life-critical	O
and	O
mission-critical	O
systems	O
.	O
</s>
<s>
The	O
Plessey	B-Device
System	I-Device
250	I-Device
was	O
a	O
system	O
originally	O
designed	O
for	O
use	O
in	O
telephony	O
switches	O
,	O
which	O
capability-based	O
design	O
was	O
chosen	O
specifically	O
for	O
reasons	O
of	O
robustness	O
.	O
</s>
<s>
In	O
contrast	O
to	O
many	O
earlier	O
systems	O
,	O
capabilities	O
are	O
the	O
only	O
mechanism	O
for	O
naming	O
and	O
using	O
resources	O
in	O
EROS	B-Operating_System
,	O
making	O
it	O
what	O
is	O
sometimes	O
referred	O
to	O
as	O
a	O
pure	O
capability	O
system	O
.	O
</s>
<s>
In	O
contrast	O
,	O
IBM	B-Application
i	I-Application
is	O
an	O
example	O
of	O
a	O
commercially	O
successful	O
capability	O
system	O
,	O
but	O
it	O
is	O
not	O
a	O
pure	O
capability	O
system	O
.	O
</s>
<s>
Confinement	O
,	O
which	O
is	O
the	O
fundamental	O
building	O
block	O
of	O
isolation	O
,	O
has	O
been	O
formally	O
verified	O
to	O
be	O
enforceable	O
by	O
pure	O
capability	O
systems	O
,	O
and	O
is	O
reduced	O
to	O
practical	O
implementation	O
by	O
the	O
EROS	B-Operating_System
constructor	O
and	O
the	O
KeyKOS	B-Operating_System
factory	O
.	O
</s>
<s>
There	O
is	O
a	O
fundamental	O
result	O
in	O
the	O
literature	O
showing	O
that	O
safety	O
is	O
mathematically	O
undecidable	O
in	O
the	O
general	O
case	O
(	O
see	O
HRU	B-Protocol
,	O
but	O
note	O
that	O
it	O
is	O
of	O
course	O
provable	O
for	O
an	O
unbounded	O
set	O
of	O
restricted	O
cases	O
)	O
.	O
</s>
<s>
Of	O
greater	O
practical	O
importance	O
,	O
safety	O
has	O
been	O
shown	O
to	O
be	O
false	O
for	O
all	O
of	O
the	O
primitive	O
protection	O
mechanisms	O
shipping	O
in	O
current	O
commodity	B-General_Concept
operating	I-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
Neither	O
EROS	B-Operating_System
nor	O
KeyKOS	B-Operating_System
has	O
ever	O
been	O
successfully	O
penetrated	O
,	O
and	O
their	O
isolation	O
mechanisms	O
have	O
never	O
been	O
successfully	O
defeated	O
by	O
any	O
inside	O
attacker	O
,	O
but	O
it	O
is	O
not	O
known	O
whether	O
the	O
two	O
implementations	O
were	O
careful	O
enough	O
.	O
</s>
<s>
The	O
L4.sec	O
system	O
,	O
which	O
is	O
a	O
successor	O
to	O
the	O
L4	B-Operating_System
microkernel	I-Operating_System
family	I-Operating_System
,	O
is	O
a	O
capability-based	O
system	O
,	O
and	O
has	O
been	O
significantly	O
influenced	O
by	O
the	O
results	O
of	O
the	O
EROS	B-Operating_System
project	O
.	O
</s>
<s>
The	O
influence	O
is	O
mutual	O
,	O
since	O
the	O
EROS	B-Operating_System
work	O
on	O
high-performance	O
invocation	O
was	O
motivated	O
strongly	O
by	O
Jochen	O
Liedtke	O
's	O
successes	O
with	O
the	O
L4	B-Operating_System
microkernel	I-Operating_System
family	I-Operating_System
.	O
</s>
<s>
The	O
primary	O
developer	O
of	O
EROS	B-Operating_System
was	O
Jonathan	O
S	O
.	O
Shapiro	O
.	O
</s>
<s>
He	O
was	O
also	O
the	O
driving	O
force	O
behind	O
Coyotos	O
,	O
which	O
was	O
an	O
"	O
evolutionary	O
step	O
"	O
beyond	O
the	O
EROS	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
.	O
</s>
<s>
The	O
EROS	B-Operating_System
project	O
started	O
in	O
1991	O
as	O
a	O
clean-room	O
reconstruction	O
of	O
an	O
earlier	O
operating	B-General_Concept
system	I-General_Concept
,	O
KeyKOS	B-Operating_System
.	O
</s>
<s>
KeyKOS	B-Operating_System
was	O
developed	O
by	O
Key	O
Logic	O
,	O
Inc.	O
,	O
and	O
was	O
a	O
direct	O
continuation	O
of	O
work	O
on	O
the	O
earlier	O
Great	O
New	O
Operating	B-General_Concept
System	I-General_Concept
In	O
the	O
Sky	O
(	O
GNOSIS	B-Operating_System
)	O
system	O
created	O
by	O
Tymshare	O
,	O
Inc	O
.	O
</s>
<s>
The	O
circumstances	O
surrounding	O
Key	O
Logic	O
's	O
demise	O
in	O
1991	O
made	O
licensing	O
KeyKOS	B-Operating_System
impractical	O
.	O
</s>
<s>
Since	O
KeyKOS	B-Operating_System
did	O
not	O
run	O
on	O
popular	O
commodity	O
processors	O
in	O
any	O
case	O
,	O
the	O
decision	O
was	O
made	O
to	O
reconstruct	O
it	O
from	O
the	O
publicly	O
available	O
documentation	O
.	O
</s>
<s>
Microkernel-based	O
systems	O
,	O
which	O
similarly	O
favor	O
large	O
numbers	O
of	O
processes	O
and	O
IPC	O
,	O
were	O
facing	O
severe	O
performance	O
challenges	O
,	O
and	O
it	O
was	O
uncertain	O
if	O
these	O
could	O
be	O
successfully	O
resolved	O
.	O
</s>
<s>
The	O
x86	B-Operating_System
architecture	I-Operating_System
was	O
clearly	O
emerging	O
as	O
the	O
dominant	O
architecture	O
but	O
the	O
expensive	O
user/supervisor	O
transition	O
latency	O
on	O
the	O
386	B-General_Concept
and	O
486	B-General_Concept
presented	O
serious	O
challenges	O
for	O
process-based	O
isolation	O
.	O
</s>
<s>
The	O
EROS	B-Operating_System
project	O
was	O
turning	O
into	O
a	O
research	O
effort	O
,	O
and	O
moved	O
to	O
the	O
University	O
of	O
Pennsylvania	O
to	O
become	O
the	O
focus	O
of	O
Shapiro	O
's	O
dissertation	O
research	O
.	O
</s>
<s>
By	O
1999	O
,	O
a	O
high	O
performance	O
implementation	O
for	O
the	O
Pentium	B-General_Concept
processor	O
had	O
been	O
demonstrated	O
that	O
was	O
directly	O
performance	O
competitive	O
with	O
the	O
L4	B-Operating_System
microkernel	I-Operating_System
family	I-Operating_System
,	O
which	O
is	O
known	O
for	O
its	O
exceptional	O
speed	O
in	O
IPC	O
.	O
</s>
<s>
The	O
EROS	B-Operating_System
confinement	O
mechanism	O
had	O
been	O
formally	O
verified	O
,	O
in	O
the	O
process	B-Operating_System
creating	O
a	O
general	O
formal	O
model	O
for	O
secure	O
capability	O
systems	O
.	O
</s>
<s>
At	O
Hopkins	O
,	O
the	O
goal	O
was	O
to	O
show	O
how	O
to	O
use	O
the	O
facilities	O
provided	O
by	O
the	O
EROS	B-Operating_System
kernel	B-Operating_System
to	O
construct	O
secure	O
and	O
defensible	O
servers	O
at	O
application	O
level	O
.	O
</s>
<s>
Funded	O
by	O
the	O
Defense	O
Advanced	O
Research	O
Projects	O
Agency	O
and	O
the	O
Air	O
Force	O
Research	O
Laboratory	O
,	O
EROS	B-Operating_System
was	O
used	O
as	O
the	O
basis	O
for	O
a	O
trusted	O
window	O
system	O
,	O
a	O
high-performance	O
,	O
defensible	O
network	O
stack	O
,	O
and	O
the	O
beginnings	O
of	O
a	O
secure	O
web	O
browser	O
.	O
</s>
<s>
In	O
2003	O
,	O
some	O
very	O
challenging	O
security	O
issues	O
were	O
discovered	O
that	O
are	O
intrinsic	O
to	O
any	O
system	O
architecture	O
based	O
on	O
synchronous	O
IPC	O
primitives	O
(	O
notably	O
including	O
EROS	B-Operating_System
and	O
L4	B-Operating_System
)	O
.	O
</s>
<s>
Work	O
on	O
EROS	B-Operating_System
halted	O
in	O
favor	O
of	O
Coyotos	O
,	O
which	O
resolved	O
these	O
issues	O
.	O
</s>
<s>
,	O
EROS	B-Operating_System
and	O
its	O
successors	O
are	O
the	O
only	O
widely	O
available	O
capability	O
systems	O
that	O
run	O
on	O
commodity	O
hardware	O
.	O
</s>
<s>
Work	O
on	O
EROS	B-Operating_System
and	O
Coyotos	O
by	O
the	O
original	O
group	O
has	O
halted	O
,	O
but	O
there	O
is	O
a	O
successor	O
system	O
.	O
</s>
<s>
The	O
CapROS	B-Application
system	O
is	O
building	O
directly	O
from	O
the	O
EROS	B-Operating_System
code	O
base	O
.	O
</s>
<s>
CapROS	B-Application
is	O
expected	O
to	O
be	O
released	O
in	O
various	O
commercial	O
deployments	O
.	O
</s>
