<s>
Coherent	B-Operating_System
is	O
a	O
clone	O
of	O
the	O
Unix	B-Application
operating	I-Application
system	I-Application
for	O
IBM	O
PC	O
compatibles	O
and	O
other	O
microcomputers	B-Architecture
,	O
developed	O
and	O
sold	O
by	O
the	O
now-defunct	O
Mark	O
Williams	O
Company	O
(	O
MWC	O
)	O
.	O
</s>
<s>
Historically	O
,	O
the	O
operating	O
system	O
was	O
a	O
proprietary	O
product	O
,	O
but	O
it	O
became	O
open	B-Application
source	I-Application
in	O
2015	O
,	O
released	O
under	O
the	O
BSD-3-Clause	B-Operating_System
license	O
.	O
</s>
<s>
Coherent	B-Operating_System
was	O
not	O
Unix	B-Application
;	O
the	O
Mark	O
Williams	O
Company	O
had	O
no	O
rights	O
to	O
either	O
the	O
Unix	B-Application
trademark	O
or	O
the	O
AT&	O
T/Bell	O
Labs	O
source	O
code	O
.	O
</s>
<s>
In	O
the	O
early	O
years	O
of	O
its	O
existence	O
,	O
MWC	O
received	O
a	O
visit	O
from	O
an	O
AT&T	O
delegation	O
looking	O
to	O
determine	O
whether	O
MWC	O
was	O
infringing	O
on	O
AT&T	O
Unix	B-Application
property	O
.	O
</s>
<s>
The	O
delegation	O
included	O
Dennis	O
Ritchie	O
,	O
who	O
concluded	O
that	O
"	O
it	O
was	O
very	O
hard	O
to	O
believe	O
that	O
Coherent	B-Operating_System
and	O
its	O
basic	O
applications	O
were	O
not	O
created	O
without	O
considerable	O
study	O
of	O
the	O
OS	O
code	O
and	O
details	O
of	O
its	O
applications.	O
"	O
</s>
<s>
Significant	O
contributions	O
were	O
also	O
made	O
by	O
people	O
such	O
as	O
Nigel	O
Bree	O
(	O
from	O
Auckland	O
,	O
New	O
Zealand	O
)	O
,	O
the	O
later	O
author	O
of	O
Ghost	B-Application
.	O
</s>
<s>
Coherent	B-Operating_System
was	O
originally	O
written	O
for	O
the	O
PDP-11	B-Device
range	O
of	O
minicomputers	O
in	O
1980	O
,	O
then	O
ported	O
to	O
various	O
early	O
1980s	O
microcomputer	B-Architecture
systems	O
including	O
IBM	O
PC	O
compatibles	O
and	O
machines	O
based	O
on	O
the	O
Zilog	B-Device
Z8000	I-Device
and	O
Motorola	B-Device
68000	I-Device
.	O
</s>
<s>
At	O
this	O
point	O
,	O
Coherent	B-Operating_System
2.3	O
offered	O
roughly	O
the	O
functionality	O
of	O
Version	B-Operating_System
7	I-Operating_System
Unix	I-Operating_System
on	O
PC	O
hardware	O
,	O
including	O
the	O
nroff	B-Device
formatter	O
but	O
not	O
the	O
BSD	O
extensions	O
offered	O
by	O
competing	O
Unix/clone	O
vendors	O
;	O
compared	O
to	O
its	O
competitors	O
,	O
it	O
was	O
a	O
small	O
system	O
distributed	O
on	O
only	O
seven	O
double-sided	B-Architecture
floppy	B-Device
disks	I-Device
,	O
costing	O
only	O
US$500	O
for	O
a	O
license	O
.	O
</s>
<s>
BYTE	O
in	O
1984	O
called	O
Coherent	B-Operating_System
a	O
"	O
highly	O
compatible	O
UNIX	B-Operating_System
Version	I-Operating_System
7	I-Operating_System
lookalike	O
"	O
.	O
</s>
<s>
In	O
1985	O
it	O
criticized	O
the	O
difficulty	O
of	O
installation	O
,	O
but	O
stated	O
that	O
"	O
as	O
a	O
UNIX	B-Operating_System
clone	I-Operating_System
,	O
Coherent	B-Operating_System
is	O
amazingly	O
complete	O
...	O
it	O
should	O
be	O
easy	O
to	O
port	O
programs	O
...	O
the	O
price	O
of	O
$495	O
is	O
a	O
bargain	O
"	O
.	O
</s>
<s>
Early	O
1990s	O
reviews	O
of	O
Coherent	B-Operating_System
pointed	O
out	O
that	O
the	O
system	O
was	O
much	O
smaller	O
than	O
other	O
contemporary	O
Unix	B-Application
offerings	O
,	O
as	O
well	O
as	O
less	O
expensive	O
at	O
US	O
$99.95	O
,	O
but	O
lacking	O
in	O
functionality	O
and	O
software	O
support	O
.	O
</s>
<s>
PC	O
Magazine	O
called	O
Coherent	B-Operating_System
3.0	O
a	O
"	O
time	O
capsule	O
"	O
that	O
captured	O
the	O
state	O
of	O
Unix	B-Application
in	O
the	O
late	O
1970s	O
,	O
without	O
support	O
for	O
mice	B-Device
,	O
LANs	B-General_Concept
or	O
SCSI	B-Architecture
disks	O
,	O
good	O
for	O
learning	O
basic	O
Unix	B-Application
programming	O
but	O
not	O
for	O
business	O
automation	O
.	O
</s>
<s>
A	O
review	O
in	O
the	O
AUUG	O
's	O
newsletter	O
was	O
more	O
positive	O
,	O
favorably	O
comparing	O
Coherent	B-Operating_System
to	O
MKS	B-Application
Toolkit	I-Application
,	O
Minix	B-Operating_System
and	O
Xenix	B-Application
,	O
and	O
suggesting	O
it	O
might	O
fill	O
a	O
niche	O
as	O
a	O
low-end	O
training	O
platform	O
.	O
</s>
<s>
Coherent	B-Operating_System
was	O
able	O
to	O
run	O
on	O
most	O
Intel-based	O
PCs	O
with	O
Intel	B-Device
8088	I-Device
,	O
286	B-General_Concept
,	O
386	B-General_Concept
,	O
and	O
486	B-General_Concept
processors	I-General_Concept
.	O
</s>
<s>
Coherent	B-Operating_System
version	O
3	O
for	O
Intel-based	O
PCs	O
required	O
at	O
least	O
a	O
286	B-General_Concept
,	O
Coherent	B-Operating_System
version	O
4	O
for	O
Intel-based	O
PCs	O
required	O
at	O
least	O
a	O
386	B-General_Concept
.	O
</s>
<s>
Like	O
a	O
true	O
Unix	B-Application
,	O
Coherent	B-Operating_System
was	O
able	O
to	O
multitask	B-Operating_System
and	O
support	O
multiple	O
users	O
.	O
</s>
<s>
From	O
version	O
4	O
,	O
released	O
1992	O
,	O
Coherent	B-Operating_System
also	O
had	O
support	O
for	O
X11	B-Operating_System
and	O
MGR	O
windowing	B-Application
systems	I-Application
.	O
</s>
<s>
Later	O
versions	O
of	O
Coherent	B-Operating_System
(	O
version	O
4	O
and	O
higher	O
)	O
supported	O
features	O
common	O
in	O
modern	O
Unix-like	B-Operating_System
systems	I-Operating_System
,	O
including	O
a	O
version	O
of	O
MicroEMACS	B-Language
,	O
access	O
to	O
DOS	B-Device
FAT16	B-Application
file	B-Application
systems	I-Application
,	O
an	O
optimizing	O
C	B-Language
compiler	B-Language
,	O
and	O
a	O
modified	O
version	O
of	O
Taylor	O
UUCP	B-Protocol
.	O
</s>
<s>
The	O
final	O
releases	O
of	O
Coherent	B-Operating_System
also	O
fully	O
supported	O
the	O
iBCS	B-Operating_System
COFF	O
binary	O
standard	O
,	O
which	O
allowed	O
binary	O
compatibility	O
with	O
SCO	B-Operating_System
Unix	I-Operating_System
applications	O
,	O
including	O
WordPerfect	B-Application
,	O
Lotus	B-Application
1-2-3	I-Application
,	O
and	O
several	O
Microsoft	O
applications	O
including	O
QuickBASIC	B-Language
,	O
Microsoft	B-Application
Word	I-Application
,	O
and	O
MultiPlan	B-Device
.	O
</s>
<s>
The	O
last	O
386	B-General_Concept
versions	O
supported	O
virtual	B-Architecture
memory	I-Architecture
,	O
but	O
not	O
demand	B-General_Concept
paging	I-General_Concept
.	O
</s>
<s>
A	O
Zilog	B-Device
Z8000	I-Device
port	O
of	O
Coherent	B-Operating_System
was	O
also	O
used	O
by	O
the	O
canceled	O
Commodore	B-Device
900	I-Device
system	O
.	O
</s>
<s>
In	O
1983	O
,	O
NCSC	O
(	O
a	O
subsidiary	O
of	O
Nixdorf	O
)	O
announced	O
a	O
port	O
of	O
Coherent	B-Operating_System
to	O
IBM	O
mainframes	O
,	O
in	O
the	O
form	O
of	O
a	O
Unix	B-Application
compatibility	O
subsystem	O
for	O
IBM	O
's	O
DOS/VS	B-Application
and	O
DOS/VSE	B-Application
and	O
Nixdorf	O
's	O
Edos/VS	B-Application
and	O
Edos/VSE	B-Application
operating	O
systems	O
,	O
known	O
as	O
Programmer	O
Work	O
Station/VSE	O
-Advanced	O
Functions	O
,	O
or	O
PWS/VSE	O
-AF	O
for	O
short	O
.	O
</s>
<s>
On	O
January	O
3	O
,	O
2015	O
,	O
Coherent	B-Operating_System
sources	O
were	O
released	O
under	O
the	O
BSD-3-Clause	B-Operating_System
license	O
.	O
</s>
