<s>
Helios	B-Operating_System
is	O
a	O
discontinued	O
Unix-like	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
for	O
parallel	B-Operating_System
computers	I-Operating_System
.	O
</s>
<s>
Its	O
primary	O
architecture	B-General_Concept
is	O
the	O
Inmos	B-General_Concept
Transputer	I-General_Concept
.	O
</s>
<s>
Helios	B-Operating_System
 '	O
microkernel	B-Operating_System
implements	O
a	O
distributed	O
namespace	O
and	O
messaging	O
protocol	O
,	O
through	O
which	O
services	O
are	O
accessed	O
.	O
</s>
<s>
A	O
POSIX	O
compatibility	O
library	O
enables	O
the	O
use	O
of	O
Unix	B-Application
application	O
software	O
,	O
and	O
the	O
system	O
provides	O
most	O
of	O
the	O
usual	O
Unix	B-Application
utilities	O
.	O
</s>
<s>
Work	O
on	O
Helios	B-Operating_System
began	O
in	O
the	O
autumn	O
of	O
1986	O
.	O
</s>
<s>
Its	O
success	O
was	O
limited	O
by	O
the	O
commercial	O
failure	O
of	O
the	O
Transputer	B-General_Concept
,	O
and	O
efforts	O
to	O
move	O
to	O
other	O
architectures	O
met	O
with	O
limited	O
success	O
.	O
</s>
<s>
The	O
name	O
of	O
the	O
product	O
was	O
Helios	B-Operating_System
.	O
</s>
<s>
In	O
the	O
materials	O
they	O
produced	O
,	O
Perihelion	O
Software	O
never	O
referred	O
to	O
the	O
operating	B-General_Concept
system	I-General_Concept
as	O
HeliOS	B-Operating_System
.	O
</s>
<s>
In	O
the	O
early	O
1980s	O
,	O
Tim	O
King	O
joined	O
MetaComCo	B-Device
from	O
the	O
University	O
of	O
Bath	O
,	O
bringing	O
with	O
him	O
some	O
rights	O
to	O
an	O
operating	B-General_Concept
system	I-General_Concept
called	O
TRIPOS	B-Operating_System
.	O
</s>
<s>
MetaComCo	B-Device
secured	O
a	O
contract	O
from	O
Commodore	O
to	O
work	O
on	O
AmigaOS	B-Application
,	O
with	O
the	O
AmigaDOS	B-Operating_System
component	O
being	O
derived	O
from	O
TRIPOS	B-Operating_System
.	O
</s>
<s>
In	O
1986	O
,	O
King	O
left	O
MetaComCo	B-Device
to	O
found	O
Perihelion	O
Software	O
,	O
and	O
began	O
development	O
of	O
a	O
parallel	O
operating	B-General_Concept
system	I-General_Concept
,	O
initially	O
targeted	O
at	O
the	O
INMOS	B-General_Concept
Transputer	I-General_Concept
series	O
of	O
processors	O
.	O
</s>
<s>
Helios	B-Operating_System
extended	O
TRIPOS	B-Operating_System
 '	O
use	O
of	O
a	O
light-weight	O
message	O
passing	O
architecture	B-General_Concept
to	O
networked	O
parallel	B-Operating_System
machines	I-Operating_System
.	O
</s>
<s>
Helios	B-Operating_System
1.0	O
was	O
the	O
first	O
commercial	O
release	O
in	O
the	O
summer	O
of	O
1988	O
,	O
followed	O
by	O
version	O
1.1	O
in	O
autumn	O
1989	O
,	O
1.1a	O
in	O
early	O
1990	O
,	O
1.2	O
in	O
December	O
1990	O
followed	O
by	O
1.2.1	O
and	O
1.2.2	O
updates	O
.	O
</s>
<s>
Helios	B-Operating_System
1.4	O
Alpha	O
was	O
planned	O
to	O
include	O
support	O
for	O
OpenLook	O
,	O
OpenMotif	O
,	O
KDE	O
,	O
Gnome	O
,	O
and	O
X11R6	O
support	O
for	O
the	O
Transputer	B-General_Concept
,	O
Linux	O
,	O
Solaris	O
,	O
and	O
Windows	O
.	O
</s>
<s>
Helios	B-Operating_System
was	O
designed	O
for	O
a	O
network	O
of	O
multiple	O
nodes	O
,	O
connected	O
by	O
multiple	O
high-bandwidth	O
communications	O
links	O
.	O
</s>
<s>
A	O
Helios	B-Operating_System
network	O
requires	O
at	O
least	O
one	O
I/O	O
Server	O
node	O
that	O
is	O
able	O
to	O
provide	O
a	O
file	B-Application
system	I-Application
server	O
,	O
console	B-Application
server	O
and	O
reset	O
control	O
for	O
the	O
processing	O
nodes	O
.	O
</s>
<s>
At	O
power	O
on	O
,	O
the	O
Helios	B-Operating_System
nucleus	O
is	O
bootstrapped	B-Operating_System
from	O
the	O
I/O	O
server	O
into	O
the	O
network	O
.	O
</s>
<s>
Each	O
node	O
is	O
booted	O
using	O
a	O
small	O
first-stage	O
loader	B-Application
that	O
then	O
downloads	O
and	O
initialises	O
the	O
nucleus	O
proper	O
.	O
</s>
<s>
Once	O
running	O
,	O
a	O
node	O
communicates	O
with	O
its	O
neighbours	O
,	O
booting	B-Operating_System
them	O
in	O
turn	O
,	O
if	O
required	O
.	O
</s>
<s>
The	O
Helios	B-Operating_System
nucleus	O
is	O
composed	O
of	O
the	O
kernel	O
,	O
libraries	O
,	O
loader	B-Application
service	O
and	O
the	O
processor	O
manager	O
service	O
.	O
</s>
<s>
The	O
Helios	B-Operating_System
kernel	O
is	O
effectively	O
a	O
microkernel	B-Operating_System
,	O
providing	O
a	O
minimal	O
abstraction	O
above	O
the	O
hardware	O
with	O
most	O
services	O
implemented	O
as	O
non-privileged	O
server	O
processes	O
.	O
</s>
<s>
The	O
Helios	B-Operating_System
nucleus	O
contains	O
three	O
libraries	O
:	O
the	O
system	O
,	O
server	O
and	O
utility	O
libraries	O
.	O
</s>
<s>
The	O
utility	O
library	O
provides	O
some	O
basic	O
library	O
routines	O
for	O
C	B-Language
programming	I-Language
that	O
are	O
shared	O
by	O
the	O
other	O
libraries	O
.	O
</s>
<s>
The	O
system	O
library	O
provides	O
the	O
basic	O
kernel	O
interface	O
,	O
converting	O
C	B-Language
function	O
calls	O
into	O
messages	O
sent	O
to	O
and	O
from	O
the	O
kernel	O
.	O
</s>
<s>
The	O
server	O
library	O
provides	O
name	O
space	O
support	O
functions	O
for	O
writing	O
Helios	B-Operating_System
servers	O
,	O
as	O
described	O
below	O
.	O
</s>
<s>
The	O
remaining	O
components	O
of	O
the	O
nucleus	O
are	O
the	O
loader	B-Application
and	O
processor	O
manager	O
servers	O
.	O
</s>
<s>
Once	O
the	O
kernel	O
is	O
loaded	O
,	O
these	O
processes	O
are	O
bootstrapped	B-Operating_System
,	O
and	O
they	O
integrate	O
the	O
newly	O
running	O
node	O
into	O
the	O
Helios	B-Operating_System
network	O
.	O
</s>
<s>
A	O
key	O
feature	O
in	O
Helios	B-Operating_System
is	O
its	O
distributed	O
name	O
system	O
.	O
</s>
<s>
A	O
Helios	B-Operating_System
network	O
implements	O
a	O
single	O
unified	O
name	O
space	O
,	O
with	O
a	O
virtual	O
root	O
node	O
,	O
optional	O
virtual	O
network	O
structuring	O
nodes	O
,	O
nodes	O
for	O
each	O
processor	O
,	O
and	O
sub-processor	O
name	O
spaces	O
provided	O
by	O
services	O
.	O
</s>
<s>
Names	O
are	O
similar	O
to	O
those	O
in	O
Unix	B-Application
,	O
using	O
a	O
forward	O
slash	O
separating	O
character	O
and	O
textual	O
naming	O
elements	O
.	O
</s>
<s>
Servers	O
are	O
Helios	B-Operating_System
processes	O
that	O
implement	O
the	O
General	O
Server	O
Protocol	O
,	O
typically	O
with	O
the	O
support	O
of	O
the	O
server	O
library	O
.	O
</s>
<s>
The	O
server	O
protocol	O
is	O
conceptually	O
similar	O
to	O
the	O
Unix	B-Application
VFS	B-Application
API	O
,	O
and	O
more	O
closely	O
to	O
Plan	B-Operating_System
9	I-Operating_System
's	O
9P	B-Operating_System
.	O
</s>
<s>
Similar	O
to	O
facilities	O
such	O
as	O
/proc	B-Application
in	O
Plan	B-Operating_System
9	I-Operating_System
and	O
other	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
,	O
resources	O
such	O
as	O
files	O
,	O
I/O	O
devices	O
,	O
users	O
,	O
and	O
processes	O
are	O
all	O
represented	O
as	O
virtual	O
files	O
in	O
the	O
namespace	O
served	O
by	O
their	O
managing	O
process	O
.	O
</s>
<s>
Key	O
servers	O
in	O
Helios	B-Operating_System
are	O
the	O
previously	O
mentioned	O
loader	B-Application
,	O
processor	O
manager	O
and	O
network	O
server	O
,	O
together	O
with	O
the	O
session	O
manager	O
,	O
the	O
window	O
server	O
and	O
the	O
file	O
server	O
.	O
</s>
<s>
Others	O
include	O
the	O
keyboard	O
,	O
mouse	O
,	O
RS-232	O
and	O
Centronics	B-Device
servers	O
(	O
built	O
into	O
the	O
host	O
I/O	O
server	O
)	O
,	O
the	O
null	O
server	O
(	O
like	O
Unix	B-Application
's	O
/dev/null	B-Operating_System
)	O
,	O
and	O
the	O
logger	O
server	O
(	O
like	O
Unix	B-Application
's	O
syslog	B-Protocol
)	O
.	O
</s>
<s>
From	O
a	O
user	O
's	O
perspective	O
,	O
Helios	B-Operating_System
is	O
quite	O
similar	O
to	O
Unix	B-Application
.	O
</s>
<s>
What	O
is	O
not	O
immediately	O
apparent	O
is	O
that	O
Helios	B-Operating_System
extends	O
the	O
notion	O
of	O
Unix	B-Operating_System
pipes	I-Operating_System
into	O
a	O
language	O
called	O
Component	O
Distribution	O
Language	O
(	O
CDL	O
)	O
.	O
</s>
<s>
In	O
CDL	O
,	O
a	O
typical	O
Unix	B-Application
shell	O
pipeline	B-Operating_System
such	O
as	O
is	O
called	O
a	O
task	O
force	O
,	O
and	O
is	O
transparently	O
distributed	O
by	O
the	O
Task	O
Force	O
Manager	O
server	O
across	O
the	O
available	O
CPUs	O
.	O
</s>
<s>
CDL	O
extends	O
traditional	B-Application
Unix	I-Application
syntax	O
with	O
additional	O
operators	O
for	O
bi-directional	O
pipes	B-Operating_System
,	O
sequential	O
and	O
parallel	O
process	O
farm	O
operators	O
,	O
load	O
balancing	O
and	O
resource	O
management	O
.	O
</s>
<s>
Helios	B-Operating_System
applications	O
can	O
be	O
written	O
using	O
C	B-Language
,	O
C++	B-Language
,	O
FORTRAN	B-Application
and	O
Modula-2	B-Language
.	O
</s>
<s>
The	O
POSIX	O
library	O
assists	O
in	O
porting	O
existing	O
Unix	B-Application
software	O
,	O
and	O
provides	O
a	O
familiar	O
environment	O
for	O
programmers	O
.	O
</s>
<s>
Helios	B-Operating_System
does	O
not	O
support	O
programs	O
written	O
in	O
the	O
occam	B-Language
programming	I-Language
language	I-Language
.	O
</s>
<s>
Helios	B-Operating_System
was	O
predominantly	O
intended	O
to	O
be	O
used	O
with	O
Transputer	B-General_Concept
systems	O
.	O
</s>
<s>
It	O
is	O
compatible	O
with	O
products	O
from	O
various	O
manufacturers	O
including	O
INMOS	O
 '	O
TRAM	O
systems	O
,	O
the	O
Meiko	B-Device
CS	B-Device
,	O
Parsytec	O
MultiCluster	O
and	O
SuperCluster	O
,	O
and	O
the	O
Telmat	O
T.Node	O
.	O
</s>
<s>
The	O
Atari	B-Device
Transputer	I-Device
Workstation	I-Device
was	O
perhaps	O
the	O
highest	O
profile	O
Helios	B-Operating_System
hardware	O
,	O
at	O
least	O
outside	O
academia	O
.	O
</s>
<s>
Helios	B-Operating_System
can	O
run	O
on	O
T4xx	O
and	O
T8xx	O
,	O
32-bit	O
Transputers	B-General_Concept
(	O
but	O
not	O
the	O
T2xx	O
16-bit	O
models	O
)	O
and	O
includes	O
device	O
drivers	O
for	O
various	O
SCSI	O
,	O
Ethernet	O
and	O
graphics	O
hardware	O
from	O
Inmos	O
,	O
Transtech	O
,	O
and	O
others	O
.	O
</s>
<s>
In	O
its	O
later	O
versions	O
,	O
Helios	B-Operating_System
was	O
ported	O
to	O
the	O
TI	O
TMS320C40	O
DSP	B-Architecture
and	O
to	O
the	O
ARM	B-Architecture
architecture	I-Architecture
,	O
the	O
latter	O
used	O
by	O
the	O
Active	O
Book	O
tablet	O
device	O
.	O
</s>
