<s>
General	O
Comprehensive	O
Operating	B-General_Concept
System	I-General_Concept
(	O
GCOS	O
,	O
;	O
originally	O
GECOS	O
,	O
General	O
Electric	O
Comprehensive	O
Operating	O
Supervisor	O
)	O
is	O
a	O
family	O
of	O
operating	B-General_Concept
systems	I-General_Concept
oriented	O
toward	O
the	O
36-bit	O
GE/Honeywell	O
mainframe	B-Architecture
computers	I-Architecture
.	O
</s>
<s>
The	O
operating	B-General_Concept
system	I-General_Concept
is	O
still	O
used	O
today	O
in	O
its	O
most	O
recent	O
versions	O
(	O
GCOS	O
7	O
and	O
GCOS	O
8	O
)	O
on	O
servers	O
and	O
mainframes	B-Architecture
produced	O
by	O
Groupe	O
Bull	O
,	O
primarily	O
through	O
emulation	B-Application
,	O
to	O
provide	O
continuity	O
with	O
legacy	O
mainframe	B-Architecture
environments	O
.	O
</s>
<s>
GCOS	O
7	O
and	O
GCOS	O
8	O
are	O
separate	O
branches	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
and	O
continue	O
to	O
be	O
developed	O
alongside	O
each	O
other	O
.	O
</s>
<s>
The	O
GECOS	O
operating	B-General_Concept
system	I-General_Concept
was	O
developed	O
by	O
General	O
Electric	O
for	O
the	O
36-bit	O
GE-600	B-Device
series	I-Device
in	O
1962	O
–	O
1964	O
;	O
GE	O
released	O
GECOS	O
I	O
(	O
with	O
a	O
prototype	O
635	O
)	O
in	O
April	O
1965	O
,	O
GECOS	O
II	O
in	O
November	O
1965	O
and	O
GECOS	O
III	O
(	O
with	O
time-sharing	B-General_Concept
)	O
in	O
1967	O
.	O
</s>
<s>
It	O
bore	O
a	O
close	O
resemblance	O
architecturally	O
to	O
IBSYS	B-Operating_System
on	O
the	O
IBM	B-Device
7094	I-Device
and	O
less	O
to	O
DOS/360	O
on	O
the	O
IBM	B-Application
System/360	I-Application
.	O
</s>
<s>
However	O
,	O
the	O
GE	O
600	O
Series	O
four	O
processor	O
architecture	O
was	O
very	O
different	O
from	O
the	O
System/360	B-Application
and	O
GECOS	O
was	O
more	O
ambitious	O
than	O
DOS/360	O
.	O
</s>
<s>
GECOS-III	O
supported	O
both	O
time-sharing	B-General_Concept
(	O
TSS	O
)	O
and	O
batch	B-General_Concept
processing	I-General_Concept
,	O
with	O
dynamic	O
allocation	O
of	O
memory	O
(	O
IBM	O
had	O
fixed	O
partitions	O
,	O
at	O
that	O
time	O
)	O
,	O
making	O
it	O
a	O
true	O
second-generation	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
After	O
Honeywell	O
acquired	O
GE	O
's	O
computer	O
division	O
,	O
GECOS-III	O
was	O
renamed	O
GCOS	O
3	O
,	O
and	O
the	O
hardware	O
line	O
was	O
renamed	O
to	O
the	O
H-6000	B-Device
adding	O
the	O
EIS	O
(	O
enhanced	O
instruction	O
set	O
,	O
character	O
oriented	O
instead	O
of	O
word	O
oriented	O
)	O
.	O
</s>
<s>
The	O
name	O
"	O
GCOS	O
"	O
was	O
extended	O
to	O
the	O
operating	B-General_Concept
systems	I-General_Concept
for	O
all	O
Honeywell-marketed	O
product	O
lines	O
.	O
</s>
<s>
GCOS-64	O
,	O
a	O
completely	O
different	O
32-bit	O
operating	B-General_Concept
system	I-General_Concept
for	O
the	O
Level	O
64	O
series	O
,	O
similar	O
to	O
a	O
parallel	O
development	O
called	O
Multics	B-Application
,	O
was	O
designed	O
by	O
Honeywell	O
and	O
Honeywell	O
Bull	O
developers	O
in	O
France	O
and	O
Boston	O
.	O
</s>
<s>
GCOS-62	O
,	O
the	O
operating	B-General_Concept
system	I-General_Concept
for	O
another	O
32-bit	O
low-end	O
line	O
of	O
machines	O
,	O
the	O
Level	O
62	O
series	O
,	O
was	O
designed	O
in	O
Italy	O
.	O
</s>
<s>
GCOS-61	O
was	O
the	O
operating	B-General_Concept
system	I-General_Concept
for	O
a	O
new	O
version	O
of	O
a	O
small	O
system	O
made	O
in	O
France	O
(	O
Model	O
58	O
,	O
later	O
Level	O
61/58	O
)	O
,	O
and	O
the	O
operating	B-General_Concept
system	I-General_Concept
for	O
a	O
new	O
16-bit	O
minicomputer	B-Architecture
line	O
from	O
Massachusetts	O
(	O
Billerica	O
)	O
,	O
the	O
Level	O
6	O
,	O
got	O
the	O
name	O
GCOS	O
6	O
.	O
</s>
<s>
Operating	B-General_Concept
Systems	I-General_Concept
retained	O
the	O
GCOS	O
brand-name	O
,	O
with	O
GCOS	O
6	O
,	O
GCOS	O
4	O
,	O
GCOS	O
7	O
,	O
and	O
GCOS	O
8	O
being	O
introduced	O
.	O
</s>
<s>
Honeywell	O
Bull	O
published	O
"	O
Large	O
Systems	O
:	O
GCOS	O
8	O
OS	O
Time	B-General_Concept
Sharing	I-General_Concept
System	O
User	O
's	O
Guide	O
"	O
in	O
1986	O
.	O
</s>
<s>
DPS	O
6	O
and	O
DPS	O
4	O
(	O
ex-Level	O
62	O
)	O
were	O
superseded	O
by	O
Motorola	B-Device
68000	I-Device
and	O
later	O
on	O
PowerPC	B-Architecture
minicomputers	B-Architecture
running	O
Unix	B-Application
and	O
the	O
product	O
lines	O
were	O
discontinued	O
,	O
though	O
GCOS	O
6	O
ran	O
in	O
an	O
emulator	B-Application
on	O
top	O
of	O
AIX	B-Application
.	O
</s>
<s>
NEC	O
supplied	O
several	O
generations	O
of	O
mainframe	B-Architecture
hardware	O
at	O
the	O
high	O
end	O
,	O
which	O
would	O
run	O
both	O
GCOS	O
8	O
and	O
their	O
own	O
ACOS-4	B-Application
Operating	B-General_Concept
System	I-General_Concept
.	O
</s>
<s>
Bull	O
used	O
the	O
nomenclature	O
DPS-9000	O
for	O
its	O
entire	O
GCOS	O
8-based	O
mainframe	B-Architecture
line	O
,	O
which	O
included	O
models	O
designed	O
by	O
both	O
Bull	O
and	O
NEC	O
.	O
</s>
<s>
This	O
platform	O
,	O
called	O
Novascale	O
and	O
based	O
on	O
Itanium	O
2	O
processors	O
,	O
ran	O
both	O
Windows	B-Application
and	O
Linux	B-Application
natively	O
.	O
</s>
<s>
However	O
,	O
Instruction	B-Application
Set	I-Application
Simulators	I-Application
for	O
both	O
the	O
DPS	O
7000	O
and	O
DPS	O
9000	O
allowed	O
GCOS	O
7	O
and	O
GCOS	O
8	O
to	O
run	O
on	O
this	O
platform	O
.	O
</s>
<s>
The	O
demise	O
of	O
the	O
Itanium	O
family	O
required	O
a	O
change	O
of	O
hardware	O
,	O
and	O
as	O
of	O
2022	O
,	O
GCOS	O
7	O
and	O
GCOS	O
8	O
are	O
simulated	O
on	O
Bull	O
Sequana	O
M7200	O
and	O
M9600	O
Xeon-based	O
hardware	O
respectively	O
.	O
</s>
<s>
A	O
trace	O
of	O
GCOS	O
influence	O
remains	O
today	O
in	O
modern	O
UNIX	B-Application
systems	I-Application
.	O
</s>
<s>
Some	O
early	O
Unix	B-Application
systems	I-Application
at	O
Bell	O
Labs	O
used	O
GCOS	O
machines	O
for	O
print	O
spooling	O
and	O
various	O
other	O
services	O
.	O
</s>
<s>
The	O
field	O
added	O
to	O
"	O
/etc/passwd	O
"	O
to	O
carry	O
GCOS	O
ID	O
information	O
was	O
called	O
the	O
"	O
GECOS	B-Operating_System
field	I-Operating_System
"	O
and	O
survives	O
today	O
as	O
the	O
"	O
pw_gecos	O
"	O
member	O
used	O
for	O
the	O
user	O
's	O
full	O
name	O
and	O
other	O
human-ID	O
information	O
.	O
</s>
<s>
Multics	B-Application
today	O
,	O
under	O
the	O
"	O
simh	B-Application
"	O
simulator	O
,	O
retains	O
the	O
capability	O
of	O
running	O
GCOS	O
jobs	O
,	O
both	O
batch	O
and	O
timesharing	B-General_Concept
,	O
via	O
the	O
"	O
Multics	B-Application
GCOS	O
Environment	O
Simulator.	O
"	O
</s>
<s>
GCOS	O
3	O
(	O
and	O
later	O
GCOS	O
7	O
and	O
GCOS	O
8	O
)	O
featured	O
a	O
good	O
Codasyl	B-Language
network	O
database	B-Application
called	O
Integrated	B-Application
Data	I-Application
Store	I-Application
(	O
IDS	O
)	O
that	O
was	O
the	O
model	O
for	O
the	O
more	O
successful	O
IDMS	B-Application
.	O
</s>
<s>
Several	O
transaction	B-General_Concept
processing	I-General_Concept
monitors	I-General_Concept
were	O
designed	O
for	O
GCOS	O
3	O
and	O
GCOS	O
8	O
.	O
</s>
<s>
An	O
early	O
attempt	O
at	O
Transaction	B-General_Concept
processing	I-General_Concept
(	O
TP	O
)	O
for	O
GCOS	O
3	O
,	O
the	O
Transaction	B-General_Concept
Processing	I-General_Concept
Executive	O
,	O
assumed	O
that	O
,	O
as	O
in	O
Unix	B-Application
,	O
a	O
new	O
process	B-Operating_System
should	O
be	O
started	O
to	O
handle	O
each	O
transaction	B-General_Concept
,	O
and	O
enjoyed	O
only	O
very	O
limited	O
success	O
.	O
</s>
<s>
Another	O
TP	O
system	O
,	O
the	O
Transaction	B-General_Concept
Driven	O
System	O
(	O
TDS	O
)	O
,	O
was	O
soon	O
developed	O
for	O
GCOS	O
3	O
,	O
using	O
a	O
single	O
process	B-Operating_System
(	O
potentially	O
with	O
multiple	O
threads	O
)	O
to	O
service	O
all	O
transactions	O
.	O
</s>
<s>
It	O
was	O
later	O
replaced	O
by	O
the	O
backward-compatible	O
Transaction	B-General_Concept
Processing	I-General_Concept
8	O
(	O
TP8	O
)	O
on	O
GCOS	O
8	O
,	O
which	O
profited	O
from	O
the	O
overhaul	O
in	O
GCOS	O
system	O
architecture	O
that	O
came	O
with	O
GCOS	O
8	O
to	O
make	O
full	O
use	O
of	O
virtual	O
memory	O
concepts	O
.	O
</s>
<s>
TP8	O
used	O
multiple	O
static	O
processes	O
in	O
a	O
way	O
similar	O
to	O
UNIX	B-Application
daemons	O
to	O
handle	O
incoming	O
transactions	O
in	O
a	O
multiplexed	O
way	O
.	O
</s>
<s>
GCOS	O
is	O
a	O
multithreading	O
,	O
multiprogramming	O
operating	B-General_Concept
system	I-General_Concept
originally	O
oriented	O
towards	O
batch	B-General_Concept
processing	I-General_Concept
,	O
although	O
later	O
versions	O
incorporated	O
enhancements	O
for	O
timesharing	B-General_Concept
and	O
online	O
transaction	B-General_Concept
processing	I-General_Concept
environments	O
.	O
</s>
<s>
GCOS	O
has	O
a	O
basic	O
architecture	O
similar	O
to	O
that	O
of	O
operating	B-General_Concept
systems	I-General_Concept
for	O
the	O
IBM	B-Application
360	I-Application
and	O
earlier	O
IBM	O
7090	O
Series	O
,	O
and	O
subsequent	O
operating	B-General_Concept
systems	I-General_Concept
with	O
which	O
it	O
competed	O
.	O
</s>
<s>
It	O
was	O
also	O
heavily	O
influenced	O
by	O
projects	O
such	O
as	O
MEDINET	O
,	O
Multics	B-Application
,	O
and	O
WWMCCS	O
,	O
and	O
has	O
inherited	O
a	O
strong	O
security	O
structure	O
in	O
consequence	O
.	O
</s>
<s>
Hardware	O
and	O
software	O
features	O
combine	O
to	O
render	O
the	O
operating	B-General_Concept
system	I-General_Concept
unusually	O
secure	O
for	O
an	O
operating	B-General_Concept
system	I-General_Concept
of	O
its	O
generation	O
and	O
class	O
.	O
</s>
<s>
Multics	B-Application
influenced	O
the	O
design	O
of	O
the	O
hardware	O
,	O
with	O
gate-oriented	O
secure	O
transfer-of-control	O
instructions	O
and	O
a	O
hardware-enforced	O
system	O
of	O
security	O
levels	O
very	O
similar	O
to	O
that	O
of	O
the	O
famous	O
Multics	B-Application
rings	O
.	O
</s>
<s>
Early	O
versions	O
of	O
GCOS	O
and	O
the	O
hardware	O
it	O
ran	O
on	O
did	O
not	O
support	O
paged	O
virtual	O
memory	O
but	O
did	O
support	O
a	O
single	O
memory	O
segment	O
per	O
process	B-Operating_System
.	O
</s>
<s>
This	O
made	O
it	O
inferior	O
for	O
time-sharing	B-General_Concept
,	O
especially	O
compared	O
with	O
hardware	O
designed	O
to	O
support	O
Multics	B-Application
and	O
the	O
contemporaneous	O
DEC	B-Device
PDP-10	I-Device
hardware	O
.	O
</s>
<s>
GCOS	O
is	O
a	O
process-oriented	O
OS	O
,	O
in	O
which	O
each	O
process	B-Operating_System
hosts	O
one	O
or	O
more	O
execution	O
threads	O
and	O
executes	O
in	O
its	O
own	O
virtual	O
memory	O
space	O
.	O
</s>
<s>
Virtual	O
memory	O
is	O
divided	O
into	O
segments	O
of	O
arbitrary	O
size	O
reminiscent	O
of	O
Multics	B-Application
segments	O
,	O
and	O
a	O
second	O
level	O
of	O
address	O
translation	O
converts	O
pure	O
virtual	O
addresses	O
to	O
pageable	O
addresses	O
,	O
which	O
are	O
then	O
converted	O
to	O
real	O
addresses	O
in	O
main	O
memory	O
or	O
backing	O
store	O
.	O
</s>
<s>
The	O
top-level	O
virtual	O
memory	O
architecture	O
also	O
simplifies	O
sharing	O
of	O
code	O
and	O
data	O
in	O
a	O
secure	O
fashion	O
,	O
again	O
in	O
a	O
way	O
reminiscent	O
of	O
Multics	B-Application
.	O
</s>
<s>
The	O
most	O
recent	O
machines	O
capable	O
of	O
running	O
the	O
OS	O
do	O
so	O
through	O
emulation	B-Application
of	O
that	O
hardware	O
.	O
</s>
<s>
The	O
hardware	O
originally	O
had	O
much	O
in	O
common	O
with	O
Multics	B-Application
hardware	O
,	O
so	O
much	O
so	O
that	O
some	O
mainframe	B-Architecture
equipment	O
could	O
be	O
switched	O
from	O
"	O
GCOS	O
mode	O
"	O
to	O
"	O
Multics	B-Application
mode	O
"	O
with	O
the	O
turn	O
of	O
a	O
dial	O
.	O
</s>
<s>
Much	O
of	O
the	O
peripheral	O
equipment	O
used	O
with	O
GCOS	O
could	O
also	O
be	O
used	O
with	O
Multics	B-Application
,	O
although	O
front-end	O
network	O
processors	O
were	O
very	O
different	O
between	O
the	O
two	O
systems	O
.	O
</s>
<s>
Program	O
languages	O
available	O
for	O
GCOS	O
included	O
GCOS	O
Algol	O
,	O
Algol-68	B-Language
,	O
COBOL	B-Application
,	O
SNOBOL	B-Application
,	O
JOVIAL	B-Language
,	O
APL	B-Language
,	O
FORTRAN	O
68	O
,	O
CORAL	B-Language
66	I-Language
,	O
FORTRAN	O
77	O
,	O
and	O
B	B-Language
.	O
</s>
<s>
Modern	O
terminology	O
for	O
units	O
of	O
storage	O
applies	O
across	O
various	O
operating	B-General_Concept
systems	I-General_Concept
and	O
computer	O
vendors	O
,	O
and	O
is	O
part	O
of	O
everyday	O
conversation	O
.	O
</s>
<s>
Since	O
the	O
early	O
1970s	O
,	O
all	O
GCOS	O
3	O
and	O
GCOS	O
8	O
disk	O
drives	O
used	O
Logical	B-Device
Block	I-Device
Addressing	I-Device
(	O
LBA	O
)	O
.	O
</s>
