<s>
The	O
architecture	B-Operating_System
of	I-Operating_System
macOS	I-Operating_System
describes	O
the	O
layers	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
that	O
is	O
the	O
culmination	O
of	O
Apple	O
Inc.	O
'	O
s	O
decade-long	O
research	O
and	O
development	O
process	O
to	O
replace	O
the	O
classic	B-Application
Mac	I-Application
OS	I-Application
.	O
</s>
<s>
After	O
the	O
failures	O
of	O
their	O
previous	O
attempts	O
—	O
Pink	O
,	O
which	O
started	O
as	O
an	O
Apple	O
project	O
but	O
evolved	O
into	O
a	O
joint	O
venture	O
with	O
IBM	O
called	O
Taligent	B-Operating_System
,	O
and	O
Copland	B-Application
,	O
which	O
started	O
in	O
1994	O
and	O
was	O
cancelled	O
two	O
years	O
later	O
—	O
Apple	O
began	O
development	O
of	O
Mac	B-Application
OS	I-Application
X	O
,	O
later	O
renamed	O
OS	O
X	O
and	O
then	O
macOS	B-Application
,	O
with	O
the	O
acquisition	O
of	O
NeXT	O
's	O
NeXTSTEP	B-Application
in	O
1997	O
.	O
</s>
<s>
NeXTSTEP	B-Application
used	O
a	O
hybrid	O
kernel	O
that	O
combined	O
the	O
Mach	B-Operating_System
2.5	I-Operating_System
kernel	O
developed	O
at	O
Carnegie	O
Mellon	O
University	O
with	O
subsystems	O
from	O
4.3BSD	O
.	O
</s>
<s>
NeXTSTEP	B-Application
also	O
introduced	O
a	O
new	O
windowing	O
system	O
based	O
on	O
Display	O
PostScript	O
that	O
intended	O
to	O
achieve	O
better	O
WYSIWYG	B-Application
systems	O
by	O
using	O
the	O
same	O
language	O
to	O
draw	O
content	O
on	O
monitors	O
that	O
drew	O
content	O
on	O
printers	O
.	O
</s>
<s>
NeXT	O
also	O
included	O
object-oriented	B-Language
programming	I-Language
tools	O
based	O
on	O
the	O
Objective-C	B-Language
language	O
that	O
they	O
had	O
acquired	O
from	O
Stepstone	O
and	O
a	O
collection	O
of	O
Frameworks	O
(	O
or	O
Kits	O
)	O
that	O
were	O
intended	O
to	O
speed	O
software	O
development	O
.	O
</s>
<s>
NeXTSTEP	B-Application
originally	O
ran	O
on	O
Motorola	O
's	O
68k	B-Device
processors	O
,	O
but	O
was	O
later	O
ported	O
to	O
Intel	O
's	O
x86	B-Operating_System
,	O
Hewlett-Packard	O
'	O
s	O
PA-RISC	B-Device
and	O
Sun	O
Microsystems	O
 '	O
SPARC	B-Architecture
processors	O
.	O
</s>
<s>
Later	O
on	O
,	O
the	O
developer	O
tools	O
and	O
frameworks	O
were	O
released	O
,	O
as	O
OpenStep	B-Operating_System
,	O
as	O
a	O
development	O
platform	O
that	O
would	O
run	O
on	O
other	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
On	O
February	O
4	O
,	O
1997	O
,	O
Apple	O
acquired	O
NeXT	O
and	O
began	O
development	O
of	O
the	O
Rhapsody	B-Operating_System
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Rhapsody	B-Operating_System
built	O
on	O
NeXTSTEP	B-Application
,	O
porting	O
the	O
core	O
system	O
to	O
the	O
PowerPC	B-Architecture
architecture	O
and	O
adding	O
a	O
redesigned	O
user	O
interface	O
based	O
on	O
the	O
Platinum	B-Operating_System
user	O
interface	O
from	O
Mac	B-Operating_System
OS	I-Operating_System
8	I-Operating_System
.	O
</s>
<s>
An	O
emulation	O
layer	O
called	O
Blue	O
Box	O
allowed	O
Mac	B-Application
OS	I-Application
applications	O
to	O
run	O
within	O
an	O
actual	O
instance	O
of	O
the	O
Mac	B-Application
OS	I-Application
and	O
an	O
integrated	O
Java	B-Device
platform	I-Device
.	O
</s>
<s>
The	O
Objective-C	B-Language
developer	O
tools	O
and	O
Frameworks	O
were	O
referred	O
to	O
as	O
the	O
Yellow	B-Operating_System
Box	I-Operating_System
and	O
also	O
made	O
available	O
separately	O
for	O
Microsoft	B-Application
Windows	I-Application
.	O
</s>
<s>
The	O
Rhapsody	B-Operating_System
project	O
eventually	O
bore	O
the	O
fruit	O
of	O
all	O
Apple	O
's	O
efforts	O
to	O
develop	O
a	O
new	O
generation	O
Mac	B-Application
OS	I-Application
,	O
which	O
finally	O
shipped	O
in	O
the	O
form	O
of	O
Mac	B-Operating_System
OS	I-Operating_System
X	I-Operating_System
Server	I-Operating_System
.	O
</s>
<s>
At	O
the	O
1998	O
Worldwide	O
Developers	O
Conference	O
(	O
WWDC	O
)	O
,	O
Apple	O
announced	O
a	O
move	O
that	O
was	O
intended	O
as	O
a	O
response	O
to	O
complaints	O
from	O
Macintosh	O
software	O
developers	O
who	O
were	O
not	O
happy	O
with	O
the	O
two	O
options	O
(	O
Yellow	B-Operating_System
Box	I-Operating_System
and	O
Blue	O
Box	O
)	O
available	O
in	O
Rhapsody	B-Operating_System
.	O
</s>
<s>
Mac	B-Application
OS	I-Application
X	O
would	O
add	O
another	O
developer	O
API	B-General_Concept
to	O
the	O
existing	O
ones	O
in	O
Rhapsody	B-Operating_System
.	O
</s>
<s>
Key	O
APIs	B-General_Concept
from	O
the	O
Macintosh	B-Device
Toolbox	I-Device
would	O
be	O
implemented	O
in	O
Mac	B-Application
OS	I-Application
X	O
to	O
run	O
directly	O
on	O
the	O
BSD	O
layers	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
instead	O
of	O
in	O
the	O
emulated	O
Macintosh	O
layer	O
.	O
</s>
<s>
This	O
modified	O
interface	O
,	O
called	O
Carbon	B-Operating_System
,	O
would	O
eliminate	O
approximately	O
2000	O
troublesome	O
API	B-General_Concept
calls	O
(	O
of	O
about	O
8000	O
total	O
)	O
and	O
replace	O
them	O
with	O
calls	O
compatible	O
with	O
a	O
modern	O
OS	O
.	O
</s>
<s>
At	O
the	O
same	O
conference	O
,	O
Apple	O
announced	O
that	O
the	O
Mach	B-Operating_System
side	O
of	O
the	O
kernel	O
had	O
been	O
updated	O
with	O
sources	O
from	O
the	O
OSFMK	O
7.3	O
(	O
Open	O
Source	O
Foundation	O
Mach	B-Operating_System
Kernel	I-Operating_System
)	O
and	O
the	O
BSD	O
side	O
of	O
the	O
kernel	O
had	O
been	O
updated	O
with	O
sources	O
from	O
the	O
FreeBSD	B-Operating_System
,	O
NetBSD	B-Device
and	O
OpenBSD	B-Operating_System
projects	I-Operating_System
.	O
</s>
<s>
They	O
also	O
announced	O
a	O
new	O
driver	O
model	O
called	O
I/O	O
Kit	O
,	O
intended	O
to	O
replace	O
the	O
Driver	O
Kit	O
used	O
in	O
NeXTSTEP	B-Application
citing	O
Driver	O
Kit	O
's	O
lack	O
of	O
power	O
management	O
and	O
hot-swap	O
capabilities	O
and	O
its	O
lack	O
of	O
automatic	O
configuration	O
capability	O
.	O
</s>
<s>
At	O
the	O
1999	O
WWDC	O
,	O
Apple	O
revealed	O
Quartz	B-Operating_System
,	O
a	O
new	O
Portable	B-Application
Document	I-Application
Format	I-Application
(	O
PDF	B-Application
)	O
based	O
windowing	O
system	O
for	O
the	O
operating	B-General_Concept
system	I-General_Concept
that	O
was	O
not	O
encumbered	O
with	O
licensing	O
fees	O
to	O
Adobe	O
like	O
the	O
Display	O
PostScript	O
windowing	O
system	O
of	O
NeXTSTEP	B-Application
.	O
</s>
<s>
Apple	O
also	O
announced	O
that	O
the	O
Yellow	B-Operating_System
Box	I-Operating_System
layer	O
had	O
been	O
renamed	O
Cocoa	B-Operating_System
and	O
began	O
to	O
move	O
away	O
from	O
their	O
commitment	O
to	O
providing	O
the	O
Yellow	B-Operating_System
Box	I-Operating_System
on	O
Windows	O
.	O
</s>
<s>
At	O
this	O
WWDC	O
,	O
Apple	O
also	O
showed	O
Mac	B-Application
OS	I-Application
X	O
booting	O
off	O
of	O
a	O
HFS	B-Application
Plus	I-Application
formatted	O
drive	O
for	O
the	O
first	O
time	O
.	O
</s>
<s>
The	O
first	O
public	O
release	O
of	O
Mac	B-Application
OS	I-Application
X	O
released	O
to	O
consumers	O
was	O
a	O
Public	B-Operating_System
Beta	I-Operating_System
released	O
on	O
September	O
13	O
,	O
2000	O
.	O
</s>
