<s>
Two	O
major	O
families	O
of	O
Mac	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
were	O
developed	O
by	O
Apple	O
Inc	O
.	O
</s>
<s>
In	O
1984	O
,	O
Apple	O
debuted	O
the	O
operating	B-General_Concept
system	I-General_Concept
that	O
is	O
now	O
known	O
as	O
the	O
"	B-Application
Classic	I-Application
"	I-Application
Mac	I-Application
OS	I-Application
with	O
its	O
release	O
of	O
the	O
original	B-Operating_System
Macintosh	I-Operating_System
System	I-Operating_System
Software	I-Operating_System
.	O
</s>
<s>
The	O
system	O
,	O
rebranded	O
"	O
Mac	B-Application
OS	I-Application
"	O
in	O
1997	O
,	O
was	O
pre-installed	O
on	O
every	O
Macintosh	B-Device
until	O
2002	O
and	O
offered	O
on	O
Macintosh	B-Device
clones	I-Device
for	O
a	O
short	O
time	O
in	O
the	O
1990s	O
.	O
</s>
<s>
Noted	O
for	O
its	O
ease	B-General_Concept
of	I-General_Concept
use	I-General_Concept
,	O
it	O
was	O
also	O
criticized	O
for	O
its	O
lack	O
of	O
modern	O
technologies	O
compared	O
to	O
its	O
competitors	O
.	O
</s>
<s>
The	O
current	O
Mac	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
is	O
macOS	B-Application
,	O
originally	O
named	O
"	O
Mac	B-Device
OS	I-Device
X	I-Device
"	O
until	O
2012	O
and	O
then	O
"	O
OS	B-Operating_System
X	I-Operating_System
"	O
until	O
2016	O
.	O
</s>
<s>
Developed	O
between	O
1997	O
and	O
2001	O
after	O
Apple	O
's	O
purchase	O
of	O
NeXT	O
,	O
Mac	B-Device
OS	I-Device
X	I-Device
brought	O
an	O
entirely	O
new	O
architecture	O
based	O
on	O
NeXTSTEP	B-Application
,	O
a	O
Unix	B-Application
system	I-Application
,	O
that	O
eliminated	O
many	O
of	O
the	O
technical	O
challenges	O
that	O
the	O
classic	B-Application
Mac	I-Application
OS	I-Application
faced	O
.	O
</s>
<s>
The	O
current	O
macOS	B-Application
is	O
pre-installed	O
with	O
every	O
Mac	B-Device
and	O
receives	O
a	O
major	O
update	O
annually	O
.	O
</s>
<s>
It	O
is	O
the	O
basis	O
of	O
Apple	O
's	O
current	O
system	B-Application
software	I-Application
for	O
its	O
other	O
devices	O
–	O
iOS	B-Application
,	O
iPadOS	B-Operating_System
,	O
watchOS	B-Device
,	O
and	O
tvOS	B-Operating_System
.	O
</s>
<s>
Prior	O
to	O
the	O
introduction	O
of	O
Mac	B-Device
OS	I-Device
X	I-Device
,	O
Apple	O
experimented	O
with	O
several	O
other	O
concepts	O
,	O
releasing	O
different	O
products	O
designed	O
to	O
bring	O
the	O
Macintosh	B-Device
interface	O
or	O
applications	B-Application
to	O
Unix-like	B-Operating_System
systems	I-Operating_System
or	O
vice	O
versa	O
,	O
A/UX	B-Operating_System
,	O
MAE	B-Application
,	O
and	O
MkLinux	B-Application
.	O
</s>
<s>
Apple	O
's	O
effort	O
to	O
expand	O
upon	O
and	O
develop	O
a	O
replacement	O
for	O
its	O
classic	B-Application
Mac	I-Application
OS	I-Application
in	O
the	O
1990s	O
led	O
to	O
a	O
few	O
cancelled	O
projects	O
,	O
code	O
named	O
Star	B-Operating_System
Trek	I-Operating_System
,	O
Taligent	B-Operating_System
,	O
and	O
Copland	B-Application
.	O
</s>
<s>
Although	O
they	O
have	O
different	O
architectures	O
,	O
Mac	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
share	O
a	O
common	O
set	O
of	O
GUI	B-Application
principles	O
,	O
including	O
a	O
menu	O
bar	O
across	O
the	O
top	O
of	O
the	O
screen	O
;	O
the	O
Finder	B-Application
shell	B-Operating_System
,	O
featuring	O
a	O
desktop	B-Application
metaphor	I-Application
that	O
represents	O
files	B-Operating_System
and	O
applications	B-Application
using	O
icons	O
and	O
relates	O
concepts	O
like	O
directories	B-Application
and	O
file	O
deletion	O
to	O
real-world	O
objects	O
like	O
folders	O
and	O
a	O
trash	B-Application
can	I-Application
;	O
and	O
overlapping	O
windows	O
for	O
multitasking	B-Operating_System
.	O
</s>
<s>
The	O
"	B-Application
classic	I-Application
"	I-Application
Mac	I-Application
OS	I-Application
is	O
the	O
original	B-Device
Macintosh	I-Device
operating	B-General_Concept
system	I-General_Concept
that	O
was	O
introduced	O
in	O
1984	O
alongside	O
the	O
first	B-Device
Macintosh	I-Device
and	O
remained	O
in	O
primary	O
use	O
on	O
Macs	B-Device
until	O
the	O
introduction	O
of	O
Mac	B-Device
OS	I-Device
X	I-Device
in	O
2001	O
.	O
</s>
<s>
Apple	O
released	O
the	O
original	B-Device
Macintosh	I-Device
on	O
January	O
24	O
,	O
1984	O
;	O
its	O
early	B-Operating_System
system	I-Operating_System
software	I-Operating_System
was	O
partially	O
based	O
on	O
the	O
Lisa	B-Device
OS	O
and	O
the	O
Xerox	O
PARC	O
Alto	B-Device
computer	O
,	O
which	O
former	O
Apple	O
CEO	O
Steve	O
Jobs	O
previewed	O
.	O
</s>
<s>
It	O
was	O
originally	O
named	O
"	O
System	B-Application
Software	I-Application
"	O
,	O
or	O
simply	O
"	O
System	O
"	O
;	O
Apple	O
rebranded	O
it	O
as	O
"	O
Mac	B-Application
OS	I-Application
"	O
in	O
1996	O
due	O
in	O
part	O
to	O
its	O
Macintosh	B-Device
clone	I-Device
program	O
that	O
ended	O
a	O
year	O
later	O
.	O
</s>
<s>
Classic	B-Application
Mac	I-Application
OS	I-Application
is	O
characterized	O
by	O
its	O
monolithic	B-Architecture
design	O
.	O
</s>
<s>
Initial	O
versions	O
of	O
the	O
System	B-Application
Software	I-Application
run	O
one	O
application	O
at	O
a	O
time	O
.	O
</s>
<s>
System	O
5	O
introduced	O
cooperative	B-Operating_System
multitasking	I-Operating_System
.	O
</s>
<s>
System	B-Operating_System
7	I-Operating_System
supports	O
32-bit	O
memory	B-General_Concept
addressing	I-General_Concept
and	O
virtual	B-Architecture
memory	I-Architecture
,	O
allowing	O
larger	O
programs	O
.	O
</s>
<s>
Later	O
updates	O
to	O
the	O
System	B-Operating_System
7	I-Operating_System
enable	O
the	O
transition	O
to	O
the	O
PowerPC	B-Architecture
architecture	O
.	O
</s>
<s>
The	O
system	O
was	O
considered	O
user-friendly	B-General_Concept
,	O
but	O
its	O
architectural	O
limitations	O
were	O
critiqued	O
,	O
such	O
as	O
limited	O
memory	B-General_Concept
management	I-General_Concept
,	O
lack	O
of	O
protected	B-General_Concept
memory	I-General_Concept
and	O
access	O
controls	O
,	O
and	O
susceptibility	O
to	O
conflicts	O
among	O
extensions	B-Operating_System
.	O
</s>
<s>
Nine	O
major	O
versions	O
of	O
the	O
classic	B-Application
Mac	I-Application
OS	I-Application
were	O
released	O
.	O
</s>
<s>
The	O
name	O
"	O
Classic	O
"	O
that	O
now	O
signifies	O
the	O
system	O
as	O
a	O
whole	O
is	O
a	O
reference	O
to	O
a	O
compatibility	O
layer	O
that	O
helped	O
ease	O
the	O
transition	O
to	O
Mac	B-Device
OS	I-Device
X	I-Device
.	O
</s>
<s>
macOS	B-Application
(	O
originally	O
named	O
"	O
Mac	B-Device
OS	I-Device
X	I-Device
"	O
until	O
2012	O
and	O
then	O
"	O
OS	B-Operating_System
X	I-Operating_System
"	O
until	O
2016	O
)	O
is	O
the	O
current	O
Mac	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
that	O
officially	O
succeeded	O
the	O
classic	B-Application
Mac	I-Application
OS	I-Application
in	O
2001	O
.	O
</s>
<s>
Although	O
the	O
system	O
was	O
originally	O
marketed	O
as	O
simply	O
"	O
version	O
10	O
"	O
of	O
Mac	B-Application
OS	I-Application
,	O
it	O
has	O
a	B-Operating_System
history	I-Operating_System
that	I-Operating_System
is	I-Operating_System
largely	I-Operating_System
independent	I-Operating_System
of	O
the	O
classic	B-Application
Mac	I-Application
OS	I-Application
.	O
</s>
<s>
It	O
is	O
a	O
Unix-based	O
operating	B-General_Concept
system	I-General_Concept
built	O
on	O
NeXTSTEP	B-Application
and	O
other	O
technology	O
developed	O
at	O
NeXT	O
from	O
the	O
late	O
1980s	O
until	O
early	O
1997	O
,	O
when	O
Apple	O
purchased	O
the	O
company	O
and	O
its	O
CEO	O
Steve	O
Jobs	O
returned	O
to	O
Apple	O
.	O
</s>
<s>
Precursors	O
to	O
the	O
original	O
release	O
of	O
Mac	B-Device
OS	I-Device
X	I-Device
include	O
OPENSTEP	B-Operating_System
,	O
Apple	O
's	O
Rhapsody	B-Operating_System
project	O
,	O
and	O
the	O
Mac	B-Operating_System
OS	I-Operating_System
X	I-Operating_System
Public	I-Operating_System
Beta	I-Operating_System
.	O
</s>
<s>
macOS	B-Application
makes	O
use	O
of	O
the	O
BSD	B-Operating_System
codebase	O
and	O
the	O
XNU	B-Operating_System
kernel	I-Operating_System
,	O
and	O
its	O
core	O
set	O
of	O
components	O
is	O
based	O
upon	O
Apple	O
's	O
open	B-Application
source	I-Application
Darwin	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
.	O
</s>
<s>
macOS	B-Application
is	O
the	O
basis	O
for	O
some	O
of	O
Apple	O
's	O
other	O
operating	B-General_Concept
systems	I-General_Concept
,	O
including	O
iPhone	O
OS/iOS	O
,	O
iPadOS	B-Operating_System
,	O
watchOS	B-Device
,	O
and	O
tvOS	B-Operating_System
.	O
</s>
<s>
The	O
first	O
desktop	B-Device
version	O
of	O
the	O
system	O
was	O
released	O
on	O
March	O
24	O
,	O
2001	O
,	O
supporting	O
the	O
Aqua	B-Application
user	I-Application
interface	I-Application
.	O
</s>
<s>
Since	O
then	O
,	O
several	B-Operating_System
more	I-Operating_System
versions	I-Operating_System
adding	O
newer	O
features	O
and	O
technologies	O
have	O
been	O
released	O
.	O
</s>
<s>
An	O
early	O
server	B-Application
computing	I-Application
version	O
of	O
the	O
system	O
was	O
released	O
in	O
1999	O
as	O
a	O
technology	O
preview	O
.	O
</s>
<s>
Server	O
functionality	O
has	O
instead	O
been	O
offered	O
as	O
an	O
add-on	O
for	O
the	O
desktop	B-General_Concept
system	I-General_Concept
since	O
2011	O
.	O
</s>
<s>
Mac	B-Operating_System
OS	I-Operating_System
X	I-Operating_System
Server	I-Operating_System
–	O
later	O
called	O
"	O
OS	B-Operating_System
X	I-Operating_System
Server	I-Operating_System
"	O
and	O
"	O
macOS	B-Operating_System
Server	I-Operating_System
"	O
,	O
released	O
between	O
2001	O
and	O
2022	O
.	O
</s>
<s>
The	O
Apple	B-Application
Real-time	I-Application
Operating	I-Application
System	I-Application
Environment	I-Application
(	O
A/ROSE	B-Application
)	O
was	O
a	O
small	O
embedded	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
which	O
ran	O
on	O
the	O
Macintosh	B-Device
Coprocessor	O
Platform	O
,	O
an	O
expansion	B-Device
card	I-Device
for	O
the	O
Macintosh	B-Device
.	O
</s>
<s>
The	O
idea	O
was	O
to	O
offer	O
a	O
single	O
"	O
overdesigned	O
"	O
hardware	O
platform	O
on	O
which	O
third-party	O
vendors	O
could	O
build	O
practically	O
any	O
product	O
,	O
reducing	O
the	O
otherwise	O
heavy	O
workload	O
of	O
developing	O
a	O
NuBus-based	O
expansion	B-Device
card	I-Device
.	O
</s>
<s>
In	O
1988	O
,	O
Apple	O
released	O
its	O
first	O
UNIX-based	O
OS	O
,	O
A/UX	B-Operating_System
,	O
which	O
was	O
a	O
UNIX	B-Application
operating	I-Application
system	I-Application
with	O
the	O
Mac	B-Application
OS	I-Application
look	B-Application
and	I-Application
feel	I-Application
.	O
</s>
<s>
It	O
was	O
not	O
very	O
competitive	O
for	O
its	O
time	O
,	O
due	O
in	O
part	O
to	O
the	O
crowded	O
UNIX	B-Application
market	O
and	O
Macintosh	B-Device
hardware	O
lacking	O
high-end	O
design	O
features	O
present	O
on	O
workstation-class	O
computers	O
.	O
</s>
<s>
A/UX	B-Operating_System
had	O
most	O
of	O
its	O
success	O
in	O
sales	O
to	O
the	O
U.S.	O
government	O
,	O
where	O
POSIX	O
compliance	O
was	O
a	O
requirement	O
that	O
Mac	B-Application
OS	I-Application
could	O
not	O
meet	O
.	O
</s>
<s>
The	O
Macintosh	B-Application
Application	I-Application
Environment	I-Application
(	O
MAE	B-Application
)	O
was	O
a	O
software	O
package	O
introduced	O
by	O
Apple	O
in	O
1994	O
that	O
allowed	O
users	O
of	O
certain	O
Unix-based	O
computer	B-Device
workstations	I-Device
to	O
run	O
Apple	B-Device
Macintosh	I-Device
application	B-Application
software	I-Application
.	O
</s>
<s>
MAE	B-Application
used	O
the	O
X	B-Operating_System
Window	I-Operating_System
System	I-Operating_System
to	O
emulate	O
a	O
Macintosh	O
Finder-style	O
graphical	B-Application
user	I-Application
interface	I-Application
.	O
</s>
<s>
The	O
last	O
version	O
,	O
MAE	B-Application
3.0	O
,	O
was	O
compatible	O
with	O
System	B-Operating_System
7.5.3	I-Operating_System
.	O
</s>
<s>
MAE	B-Application
was	O
available	O
for	O
Sun	O
Microsystems	O
SPARCstation	B-Device
and	O
Hewlett-Packard	O
systems	O
.	O
</s>
<s>
Announced	O
at	O
the	O
1996	O
Worldwide	O
Developers	O
Conference	O
(	O
WWDC	O
)	O
,	O
MkLinux	B-Application
is	O
an	O
open	B-Application
source	I-Application
operating	B-General_Concept
system	I-General_Concept
that	O
was	O
started	O
by	O
the	O
OSF	B-Application
Research	I-Application
Institute	I-Application
and	O
Apple	O
in	O
February	O
1996	O
to	O
port	O
Linux	B-Operating_System
to	O
the	O
PowerPC	B-Architecture
platform	I-Architecture
,	O
and	O
thus	O
Macintosh	B-Device
computers	I-Device
.	O
</s>
<s>
In	O
mid	O
1998	O
,	O
the	O
community-led	O
MkLinux	B-Application
Developers	O
Association	O
took	O
over	O
development	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
MkLinux	B-Application
is	O
short	O
for	O
"	O
Microkernel	O
Linux	B-Operating_System
,	O
"	O
which	O
refers	O
to	O
the	O
project	O
's	O
adaptation	O
of	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
to	O
run	O
as	O
a	O
server	O
hosted	O
atop	O
the	O
Mach	B-Operating_System
microkernel	I-Operating_System
.	O
</s>
<s>
MkLinux	B-Application
is	O
based	O
on	O
version	O
3.0	O
of	O
Mach	B-Operating_System
.	O
</s>
<s>
Star	B-Operating_System
Trek	I-Operating_System
(	O
as	O
in	O
"	O
to	B-Operating_System
boldly	I-Operating_System
go	I-Operating_System
where	I-Operating_System
no	I-Operating_System
Mac	I-Operating_System
has	I-Operating_System
gone	I-Operating_System
before	I-Operating_System
"	O
)	O
was	O
a	O
relatively	O
unknown	O
secret	O
prototype	O
beginning	O
in	O
1992	O
,	O
whose	O
goal	O
was	O
to	O
create	O
a	O
version	O
of	O
the	O
classic	B-Application
Mac	I-Application
OS	I-Application
that	O
would	O
run	O
on	O
Intel-compatible	B-Operating_System
x86	B-Operating_System
personal	O
computers	O
.	O
</s>
<s>
In	O
partnership	O
with	O
Apple	O
and	O
with	O
support	O
from	O
Intel	O
,	O
the	O
project	O
was	O
instigated	O
by	O
Novell	O
,	O
which	O
was	O
looking	O
to	O
integrate	O
its	O
DR-DOS	B-Application
with	O
the	O
Mac	B-Application
OS	I-Application
GUI	B-Application
as	O
a	O
mutual	O
response	O
to	O
the	O
monopoly	O
of	O
Microsoft	O
's	O
Windows	B-Application
3.0	I-Application
and	O
MS-DOS	O
.	O
</s>
<s>
A	O
team	O
consisting	O
of	O
four	O
from	O
Apple	O
and	O
four	O
from	O
Novell	O
was	O
able	O
to	O
get	O
the	O
Macintosh	B-Application
Finder	I-Application
and	O
some	O
basic	O
applications	B-Application
such	O
as	O
QuickTime	B-Application
,	O
running	O
smoothly	O
on	O
the	O
x86	B-Operating_System
architecture	I-Operating_System
.	O
</s>
<s>
The	O
project	O
was	O
canceled	O
a	O
year	O
later	O
in	O
early	O
1993	O
,	O
but	O
some	O
of	O
the	O
code	O
was	O
later	O
reused	O
when	O
porting	O
the	O
Mac	B-Application
OS	I-Application
to	O
PowerPC	B-Architecture
.	O
</s>
<s>
Taligent	B-Operating_System
(	O
a	O
portmanteau	O
of	O
"	O
talent	O
"	O
and	O
"	O
intelligent	O
"	O
)	O
was	O
the	O
name	O
of	O
an	O
object-oriented	B-Application
operating	I-Application
system	I-Application
and	O
the	O
company	O
dedicated	O
to	O
producing	O
it	O
.	O
</s>
<s>
Started	O
as	O
a	O
project	O
within	O
Apple	O
to	O
provide	O
a	O
replacement	O
for	O
the	O
classic	B-Application
Mac	I-Application
OS	I-Application
,	O
it	O
was	O
later	O
spun	O
off	O
into	O
a	O
joint	O
venture	O
with	O
IBM	O
as	O
part	O
of	O
the	O
AIM	O
alliance	O
,	O
with	O
the	O
purpose	O
of	O
building	O
a	O
competing	O
platform	O
to	O
Microsoft	B-Application
Cairo	I-Application
and	O
NeXTSTEP	B-Application
.	O
</s>
<s>
The	O
development	O
process	O
never	O
worked	O
,	O
and	O
Taligent	B-Operating_System
is	O
often	O
cited	O
as	O
an	O
example	O
of	O
a	O
project	O
death	O
march	O
.	O
</s>
<s>
Copland	B-Application
was	O
a	O
project	O
at	O
Apple	O
to	O
create	O
an	O
updated	O
version	O
of	O
the	O
classic	B-Application
Mac	I-Application
OS	I-Application
.	O
</s>
<s>
It	O
was	O
to	O
have	O
introduced	O
protected	B-General_Concept
memory	I-General_Concept
,	O
preemptive	O
multitasking	B-Operating_System
and	O
a	O
number	O
of	O
new	O
underlying	O
operating	B-General_Concept
system	I-General_Concept
features	O
,	O
yet	O
still	O
be	O
compatible	O
with	O
existing	O
Mac	B-Operating_System
software	I-Operating_System
.	O
</s>
<s>
As	O
originally	O
planned	O
,	O
a	O
follow-up	O
release	O
known	O
as	O
"	O
Gershwin	O
"	O
would	O
add	O
multithreading	B-General_Concept
and	O
other	O
advanced	O
features	O
.	O
</s>
<s>
Copland	B-Application
development	O
ended	O
in	O
August	O
1996	O
,	O
and	O
in	O
December	O
1996	O
,	O
Apple	O
announced	O
that	O
it	O
was	O
buying	O
NeXT	O
for	O
its	O
NeXTSTEP	B-Application
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Before	O
the	O
arrival	O
of	O
the	O
Macintosh	B-Device
in	O
1984	O
,	O
Apple	O
's	O
history	O
of	O
operating	B-General_Concept
systems	I-General_Concept
began	O
with	O
its	O
Apple	B-Device
II	I-Device
series	I-Device
computers	O
in	O
1977	O
,	O
which	O
ran	O
Apple	B-Operating_System
DOS	I-Operating_System
,	O
ProDOS	B-Operating_System
,	O
and	O
later	O
GS/OS	B-Application
;	O
the	O
Apple	B-Device
III	I-Device
in	O
1980	O
,	O
which	O
ran	O
Apple	B-Operating_System
SOS	I-Operating_System
;	O
and	O
the	O
Apple	B-Device
Lisa	I-Device
in	O
1983	O
,	O
which	O
ran	O
Lisa	B-Device
OS	O
and	O
later	O
MacWorks	B-Application
XL	I-Application
,	O
a	O
Macintosh	B-Device
emulator	B-Application
.	O
</s>
<s>
Apple	O
also	O
developed	O
the	O
Newton	B-Device
OS	I-Device
for	O
its	O
Newton	B-Device
personal	B-Application
digital	I-Application
assistant	I-Application
from	O
1993	O
to	O
1997	O
.	O
</s>
<s>
In	O
recent	O
years	O
,	O
Apple	O
has	O
also	O
launched	O
several	O
new	O
operating	B-General_Concept
systems	I-General_Concept
based	O
on	O
the	O
core	O
of	O
macOS	B-Application
,	O
including	O
iOS	B-Application
in	O
2007	O
for	O
its	O
iPhone	B-Device
,	O
iPad	B-Device
,	O
and	O
iPod	B-Device
Touch	I-Device
mobile	B-Application
devices	I-Application
and	O
in	O
2017	O
for	O
its	O
HomePod	B-Device
smart	B-Device
speakers	I-Device
;	O
watchOS	B-Device
in	O
2015	O
for	O
the	O
Apple	B-Device
Watch	I-Device
;	O
tvOS	B-Operating_System
in	O
2015	O
for	O
the	O
Apple	B-Device
TV	I-Device
set-top	O
box	O
.	O
</s>
