<s>
Open	B-Protocol
Transport	I-Protocol
was	O
the	O
name	O
given	O
by	O
Apple	O
Inc	O
.	O
to	O
its	O
implementation	O
of	O
the	O
Unix-originated	O
System	B-Operating_System
V	I-Operating_System
STREAMS	B-Operating_System
networking	B-Protocol
stack	I-Protocol
.	O
</s>
<s>
Based	O
on	O
code	O
licensed	O
from	O
Mentat	O
's	O
Portable	B-Protocol
Streams	I-Protocol
product	O
,	O
Open	B-Protocol
Transport	I-Protocol
was	O
built	O
to	O
provide	O
the	O
classic	B-Application
Mac	I-Application
OS	I-Application
with	O
a	O
modern	O
TCP/IP	B-Protocol
implementation	O
,	O
replacing	O
MacTCP	B-Operating_System
.	O
</s>
<s>
Apple	O
also	O
added	O
its	O
own	O
implementation	O
of	O
AppleTalk	B-Application
to	O
the	O
stack	O
to	O
support	O
legacy	O
networks	O
.	O
</s>
<s>
Prior	O
to	O
the	O
release	O
of	O
Open	B-Protocol
Transport	I-Protocol
,	O
the	O
classic	B-Application
Mac	I-Application
OS	I-Application
used	O
a	O
variety	O
of	O
stand-alone	O
INITs	B-Operating_System
to	O
provide	O
networking	O
functionality	O
.	O
</s>
<s>
The	O
only	O
one	O
that	O
was	O
widely	O
used	O
throughout	O
the	O
OS	O
was	O
the	O
AppleTalk	B-Application
system	O
.	O
</s>
<s>
Among	O
the	O
other	O
protocol	B-Protocol
stacks	I-Protocol
supported	O
,	O
MacTCP	B-Operating_System
was	O
becoming	O
increasingly	O
important	O
as	O
the	O
Internet	O
boom	O
started	O
to	O
gain	O
momentum	O
.	O
</s>
<s>
MacTCP	B-Operating_System
emulated	O
the	O
Berkeley	B-Protocol
sockets	I-Protocol
system	O
,	O
widely	O
used	O
among	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
.	O
</s>
<s>
MacTCP	B-Operating_System
and	O
the	O
previous	O
generation	O
AppleTalk	B-Application
library	O
were	O
slow	O
on	O
PowerPC-based	O
Macintoshes	O
because	O
they	O
were	O
written	O
for	O
previous	O
generation	O
680x0-based	O
Macintoshes	O
and	O
therefore	O
ran	O
under	O
emulation	O
on	O
PowerPC-based	O
machines	O
.	O
</s>
<s>
MacTCP	B-Operating_System
was	O
also	O
lacking	O
in	O
features	O
,	O
however	O
,	O
and	O
a	O
major	O
upgrade	O
was	O
clearly	O
needed	O
if	O
Apple	O
was	O
to	O
keep	O
its	O
hand	O
in	O
the	O
Internet	O
market	O
.	O
</s>
<s>
Through	O
the	O
late	O
1980s	O
several	O
major	O
efforts	O
to	O
re-combine	O
the	O
many	O
Unix	B-Application
derivatives	O
into	O
a	O
single	O
system	O
were	O
underway	O
,	O
and	O
the	O
most	O
significant	O
among	O
these	O
was	O
the	O
AT&	O
T-led	O
System	B-Operating_System
V	I-Operating_System
.	O
System	B-Operating_System
V	I-Operating_System
included	O
an	O
entirely	O
new	O
networking	B-Protocol
stack	I-Protocol
,	O
STREAMS	B-Operating_System
,	O
replacing	O
the	O
existing	O
Berkeley	B-Protocol
sockets	I-Protocol
system	O
.	O
</s>
<s>
STREAMS	B-Operating_System
had	O
a	O
number	O
of	O
advantages	O
over	O
sockets	O
,	O
including	O
the	O
ability	O
to	O
support	O
multiple	O
networking	B-Protocol
stacks	I-Protocol
at	O
the	O
same	O
time	O
,	O
the	O
ability	O
to	O
plug	O
in	O
modules	O
into	O
the	O
middle	O
of	O
existing	O
stacks	O
to	O
provide	O
simple	O
mechanisms	O
for	O
filtering	O
and	O
similar	O
duties	O
,	O
while	O
offering	O
a	O
single	O
application	B-Application
programming	I-Application
interface	I-Application
to	O
the	O
user	O
programs	O
.	O
</s>
<s>
At	O
the	O
time	O
it	O
appeared	O
STREAMS	B-Operating_System
would	O
become	O
the	O
de	O
facto	O
standard	O
.	O
</s>
<s>
This	O
change	O
in	O
the	O
market	O
led	O
Apple	O
to	O
move	O
to	O
support	O
STREAMS	B-Operating_System
as	O
well	O
.	O
</s>
<s>
It	O
also	O
presented	O
two	O
practical	O
advantages	O
to	O
the	O
company	O
;	O
STREAMS	B-Operating_System
 '	O
multiprotocol	O
support	O
would	O
allow	O
them	O
to	O
support	O
both	O
TCP/IP	B-Protocol
and	O
AppleTalk	B-Application
from	O
a	O
single	O
interface	O
,	O
and	O
a	O
portable	O
cross-platform	O
version	O
of	O
STREAMS	B-Operating_System
was	O
available	O
for	O
purchase	O
commercially	O
,	O
one	O
that	O
included	O
a	O
high-quality	O
TCP	O
implementation	O
.	O
</s>
<s>
Using	O
STREAMS	B-Operating_System
also	O
appeared	O
to	O
offer	O
a	O
way	O
to	O
"	O
one	O
up	O
"	O
Microsoft	O
,	O
whose	O
own	O
TCP/IP	B-Protocol
networking	O
system	O
,	O
Winsock	B-Application
,	O
was	O
based	O
on	O
the	O
apparently	O
soon-to-be-obsolete	O
sockets	O
.	O
</s>
<s>
Open	B-Protocol
Transport	I-Protocol
was	O
introduced	O
in	O
May	O
1995	O
with	O
the	O
Power	B-Device
Mac	I-Device
9500	I-Device
.	O
</s>
<s>
It	O
was	O
included	O
with	O
System	B-Operating_System
7.5.2	I-Operating_System
,	O
a	O
release	O
for	O
the	O
new	O
PCI	B-Protocol
based	O
Power	B-Device
Macs	I-Device
,	O
and	O
became	O
available	O
for	O
older	O
hardware	O
later	O
.	O
</s>
<s>
MacTCP	B-Operating_System
was	O
not	O
supported	O
on	O
PCI-based	O
Macs	O
,	O
but	O
older	O
systems	O
could	O
switch	O
between	O
MacTCP	B-Operating_System
and	O
Open	B-Protocol
Transport	I-Protocol
using	O
a	O
Control	B-Operating_System
Panel	I-Operating_System
called	O
Network	O
Software	O
Selector	O
.	O
</s>
<s>
Unlike	O
MacTCP	B-Operating_System
,	O
Open	B-Protocol
Transport	I-Protocol
allowed	O
users	O
to	O
save	O
and	O
switch	O
between	O
configuration	O
sets	O
.	O
</s>
<s>
Developer	B-Application
opinion	O
on	O
Open	B-Protocol
Transport	I-Protocol
was	O
divided	O
.	O
</s>
<s>
Some	O
felt	O
it	O
offered	O
enormous	O
speed	O
improvements	O
over	O
MacTCP	B-Operating_System
.	O
</s>
<s>
Some	O
developers	B-Application
also	O
liked	O
it	O
because	O
it	O
was	O
flexible	O
in	O
the	O
way	O
it	O
allowed	O
protocols	O
to	O
be	O
"	O
stacked	O
"	O
to	O
apply	O
filters	O
and	O
other	O
such	O
duties	O
.	O
</s>
<s>
The	O
flexibility	O
of	O
the	O
Open	B-Protocol
Transport	I-Protocol
architecture	O
,	O
into	O
which	O
one	O
could	O
plug	O
any	O
desired	O
protocol	O
,	O
was	O
felt	O
by	O
some	O
to	O
be	O
thoroughly	O
overcomplicated	O
.	O
</s>
<s>
Additionally	O
,	O
most	O
Unix	B-Application
code	O
still	O
used	O
sockets	O
,	O
not	O
STREAMS	B-Operating_System
,	O
and	O
so	O
MacTCP	B-Operating_System
offered	O
real	O
advantages	O
in	O
terms	O
of	O
porting	O
software	O
to	O
the	O
Mac	O
.	O
</s>
<s>
The	O
vaunted	O
flexibility	O
of	O
the	O
Open	B-Protocol
Transport	I-Protocol
architecture	O
was	O
undermined	O
and	O
ultimately	O
made	O
obsolete	O
by	O
the	O
rapid	O
rise	O
of	O
TCP/IP	B-Protocol
networking	O
during	O
the	O
mid-90s	O
.	O
</s>
<s>
The	O
same	O
is	O
true	O
in	O
the	O
wider	O
Unix	B-Application
market	O
;	O
System	B-Operating_System
V	I-Operating_System
was	O
undermined	O
by	O
the	O
rapid	O
rise	O
of	O
free	O
Unix-like	B-Operating_System
systems	I-Operating_System
,	O
notably	O
Linux	B-Application
.	O
</s>
<s>
As	O
these	O
systems	O
grew	O
in	O
popularity	O
,	O
the	O
vast	O
majority	O
of	O
programmers	B-Application
ignored	O
the	O
closed	O
STREAMS	B-Operating_System
in	O
favour	O
of	O
the	O
BSD-licensed	O
Sockets	O
.	O
</s>
<s>
Open	B-Protocol
Transport	I-Protocol
was	O
abandoned	O
during	O
the	O
move	O
to	O
OS	B-Application
X	I-Application
,	O
which	O
,	O
being	O
derived	O
from	O
BSD	B-Operating_System
,	O
had	O
a	O
networking	B-Protocol
stack	I-Protocol
based	O
entirely	O
on	O
sockets	O
.	O
</s>
<s>
Open	B-Protocol
Transport	I-Protocol
received	O
deprecation	B-General_Concept
status	O
starting	O
in	O
Mac	B-Application
OS	I-Application
X	O
10.4	O
and	O
its	O
SDKs	B-Application
.	O
</s>
<s>
Open	B-Protocol
Transport	I-Protocol
support	O
was	O
removed	O
entirely	O
from	O
OS	B-Application
X	I-Application
starting	O
with	O
version	O
10.9	O
(	O
Mavericks	B-Operating_System
)	O
.	O
</s>
