<s>
Open	B-Operating_System
systems	I-Operating_System
are	O
computer	O
systems	O
that	O
provide	O
some	O
combination	O
of	O
interoperability	O
,	O
portability	B-Architecture
,	O
and	O
open	B-Application
software	I-Application
standards	O
.	O
</s>
<s>
The	O
term	O
was	O
popularized	O
in	O
the	O
early	O
1980s	O
,	O
mainly	O
to	O
describe	O
systems	O
based	O
on	O
Unix	B-Application
,	O
especially	O
in	O
contrast	O
to	O
the	O
more	O
entrenched	O
mainframes	B-Architecture
and	O
minicomputers	B-Architecture
in	O
use	O
at	O
that	O
time	O
.	O
</s>
<s>
Unlike	O
older	O
legacy	B-Device
systems	I-Device
,	O
the	O
newer	O
generation	O
of	O
Unix	B-Application
systems	I-Application
featured	O
standardized	O
programming	O
interfaces	O
and	O
peripheral	O
interconnects	O
;	O
third	O
party	O
development	O
of	O
hardware	O
and	O
software	O
was	O
encouraged	O
,	O
a	O
significant	O
departure	O
from	O
the	O
norm	O
of	O
the	O
time	O
,	O
which	O
saw	O
companies	O
such	O
as	O
Amdahl	O
and	O
Hitachi	O
going	O
to	O
court	O
for	O
the	O
right	O
to	O
sell	O
systems	O
and	O
peripherals	O
that	O
were	O
compatible	O
with	O
IBM	O
's	O
mainframes	B-Architecture
.	O
</s>
<s>
The	O
definition	O
of	O
"	O
open	B-Operating_System
system	I-Operating_System
"	O
can	O
be	O
said	O
to	O
have	O
become	O
more	O
formalized	O
in	O
the	O
1990s	O
with	O
the	O
emergence	O
of	O
independently	O
administered	O
software	O
standards	O
such	O
as	O
The	B-Application
Open	I-Application
Group	I-Application
's	O
Single	O
UNIX	B-Application
Specification	O
.	O
</s>
<s>
Although	O
computer	O
users	O
today	O
are	O
used	O
to	O
a	O
high	O
degree	O
of	O
both	O
hardware	O
and	O
software	O
interoperability	O
,	O
in	O
the	O
20th	O
century	O
the	O
open	B-Operating_System
systems	I-Operating_System
concept	O
could	O
be	O
promoted	O
by	O
Unix	B-Application
vendors	O
as	O
a	O
significant	O
differentiator	O
.	O
</s>
<s>
IBM	O
and	O
other	O
companies	O
resisted	O
the	O
trend	O
for	O
decades	O
,	O
exemplified	O
by	O
a	O
now-famous	O
warning	O
in	O
1991	O
by	O
an	O
IBM	O
account	O
executive	O
that	O
one	O
should	O
be	O
"	O
careful	O
about	O
getting	O
locked	O
into	O
open	B-Operating_System
systems	I-Operating_System
"	O
.	O
</s>
<s>
However	O
,	O
in	O
the	O
first	O
part	O
of	O
the	O
21st	O
century	O
many	O
of	O
these	O
same	O
legacy	B-Device
system	I-Device
vendors	O
,	O
particularly	O
IBM	O
and	O
Hewlett-Packard	O
,	O
began	O
to	O
adopt	O
Linux	B-Application
as	O
part	O
of	O
their	O
overall	O
sales	O
strategy	O
,	O
with	O
"	O
open	B-Application
source	I-Application
"	O
marketed	O
as	O
trumping	O
"	O
open	B-Operating_System
system	I-Operating_System
"	O
.	O
</s>
<s>
Consequently	O
,	O
an	O
IBM	O
mainframe	B-Architecture
with	O
Linux	B-Application
on	I-Application
IBM	I-Application
Z	I-Application
is	O
marketed	O
as	O
being	O
more	O
of	O
an	O
open	B-Operating_System
system	I-Operating_System
than	O
commodity	B-Device
computers	I-Device
using	O
closed-source	O
Microsoft	B-Application
Windows	I-Application
—	O
or	O
even	O
those	O
using	O
Unix	B-Application
,	O
despite	O
its	O
open	B-Operating_System
systems	I-Operating_System
heritage	O
.	O
</s>
<s>
In	O
response	O
,	O
more	O
companies	O
are	O
opening	O
the	O
source	O
code	O
to	O
their	O
products	O
,	O
with	O
a	O
notable	O
example	O
being	O
Sun	O
Microsystems	O
and	O
their	O
creation	O
of	O
the	O
OpenOffice.org	B-Application
and	O
OpenSolaris	B-Operating_System
projects	O
,	O
based	O
on	O
their	O
formerly	O
closed-source	O
StarOffice	B-Application
and	O
Solaris	B-Application
software	O
products	O
.	O
</s>
