<s>
A	O
processor	B-Device
direct	I-Device
slot	I-Device
(	O
PDS	O
)	O
is	O
a	O
slot	O
incorporated	O
into	O
many	O
older	O
Macintosh	B-Device
models	O
that	O
allowed	O
direct	O
access	O
to	O
the	O
signal	O
pins	O
of	O
a	O
CPU	O
,	O
similar	O
to	O
the	O
functionality	O
of	O
a	O
local	B-Architecture
bus	I-Architecture
in	O
PCs	B-Device
.	O
</s>
<s>
This	O
would	O
result	O
in	O
much	O
higher	O
speeds	O
than	O
having	O
to	O
go	O
through	O
a	O
bus	O
layer	O
,	O
such	O
as	O
NuBus	B-Device
,	O
which	O
typically	O
ran	O
at	O
a	O
slower	O
10MHz	O
speed	O
.	O
</s>
<s>
However	O
,	O
there	O
was	O
never	O
more	O
than	O
one	O
PDS	B-Device
slot	I-Device
,	O
as	O
rather	O
than	O
providing	O
a	O
sophisticated	O
communication	O
protocol	O
with	O
arbitration	O
between	O
different	O
bits	O
of	O
hardware	O
that	O
might	O
be	O
trying	O
to	O
use	O
the	O
communication	O
channel	O
at	O
the	O
same	O
time	O
,	O
the	O
PDS	B-Device
slot	I-Device
,	O
for	O
the	O
most	O
part	O
,	O
just	O
gave	O
direct	O
access	O
to	O
signal	O
pins	O
on	O
the	O
CPU	O
,	O
making	O
it	O
closer	O
in	O
nature	O
to	O
a	O
local	B-Architecture
bus	I-Architecture
.	O
</s>
<s>
Thus	O
,	O
PDS	B-Device
slots	I-Device
tended	O
to	O
be	O
CPU-specific	O
,	O
and	O
therefore	O
a	O
card	O
designed	O
for	O
the	O
PDS	B-Device
slot	I-Device
in	O
the	O
Motorola	O
68030-based	O
Macintosh	B-Device
SE/30	I-Device
,	O
for	O
example	O
,	O
would	O
not	O
work	O
in	O
the	O
Motorola	O
68040-based	O
Quadra	B-Device
700	I-Device
.	O
</s>
<s>
The	O
one	O
notable	O
exception	O
to	O
this	O
was	O
the	O
PDS	O
design	O
for	O
the	O
original	O
Motorola	O
68020-based	O
Macintosh	B-Device
LC	I-Device
.	O
</s>
<s>
This	O
was	O
Apple	O
's	O
first	O
attempt	O
at	O
a	O
"	O
low-cost	O
"	O
Mac	O
,	O
and	O
it	O
was	O
such	O
a	O
success	O
that	O
,	O
when	O
subsequent	O
models	O
replaced	O
the	O
CPU	O
with	O
a	O
68030	B-Device
,	O
a	O
68040	B-Device
,	O
and	O
later	O
a	O
PowerPC	B-Architecture
processor	I-Architecture
,	O
Apple	O
found	O
methods	O
to	O
keep	O
the	O
PDS	B-Device
slot	I-Device
compatible	O
with	O
the	O
original	O
LC	O
,	O
so	O
that	O
the	O
same	O
expansion	O
cards	O
would	O
continue	O
to	O
work	O
.	O
</s>
<s>
The	O
SE	O
"	O
System	O
Expansion	O
"	O
slot	O
,	O
introduced	O
in	O
the	O
Macintosh	B-Device
SE	I-Device
in	O
1987	O
,	O
was	O
the	O
first	O
processor	B-Device
direct	I-Device
slot	I-Device
,	O
using	O
a	O
96-pin	O
Euro-DIN	O
connector	O
to	O
interface	O
with	O
the	O
Motorola	B-Device
68000	I-Device
processor	I-Device
.	O
</s>
<s>
This	O
slot	O
was	O
also	O
used	O
in	O
the	O
Macintosh	B-Device
Portable	I-Device
.	O
</s>
<s>
The	O
L2	O
cache	B-General_Concept
slot	O
of	O
the	O
Macintosh	B-Device
IIci	I-Device
,	O
introduced	O
in	O
1989	O
,	O
was	O
a	O
32-bit	O
version	O
of	O
a	O
PDS	O
which	O
used	O
a	O
120-pin	O
Euro-DIN	O
connector	O
to	O
support	O
the	O
Motorola	B-Device
68030	I-Device
processor	O
.	O
</s>
<s>
This	O
slot	O
also	O
appeared	O
in	O
the	O
Macintosh	B-Device
IIsi	I-Device
,	O
IIvi	B-Device
,	O
and	O
IIvx	B-Device
.	O
</s>
<s>
The	O
Macintosh	B-Device
SE/30	I-Device
also	O
uses	O
the	O
same	O
PDS	O
configuration	O
,	O
but	O
space	O
inside	O
the	O
compact	O
Mac	O
case	O
is	O
a	O
limiting	O
factor	O
.	O
</s>
<s>
The	O
Macintosh	B-Device
IIfx	I-Device
,	O
introduced	O
in	O
1990	O
,	O
included	O
a	O
PDS	O
that	O
was	O
visually	O
similar	O
to	O
the	O
IIci	B-Device
slot	O
,	O
but	O
differences	O
in	O
pinouts	O
and	O
bus	O
mastering	O
resulted	O
in	O
very	O
limited	O
use	O
.	O
</s>
<s>
The	O
LC	O
slot	O
,	O
introduced	O
in	O
1990	O
,	O
began	O
as	O
a	O
PDS	O
for	O
the	O
Motorola	B-Device
68020	I-Device
/	O
68030	B-Device
processors	O
in	O
the	O
Macintosh	B-Device
LC	I-Device
/	O
LC	B-Device
II	I-Device
,	O
which	O
used	O
a	O
slower	O
,	O
less	O
expensive	O
16-bit	B-Device
data	O
bus	O
.	O
</s>
<s>
The	O
96-pin	O
Euro-DIN	O
connector	O
in	O
the	O
early	O
16-bit	B-Device
models	O
look	O
like	O
the	O
SE	O
slot	O
connector	O
,	O
but	O
are	O
incompatible	O
.	O
</s>
<s>
Latter	O
models	O
added	O
18	O
more	O
pins	O
through	O
a	O
notched	O
in-line	O
extension	O
to	O
support	O
a	O
32-bit	O
data	O
bus	O
,	O
while	O
retaining	O
backwards	O
compatibility	O
with	O
16-bit	B-Device
cards	O
.	O
</s>
<s>
This	O
configuration	O
proved	O
to	O
be	O
so	O
popular	O
for	O
Apple	O
's	O
Performa	B-Device
line	O
that	O
later	O
PowerPC-based	O
versions	O
were	O
essentially	O
emulating	O
the	O
68030	B-Device
pin	O
signals	O
for	O
the	O
LC	O
slots	O
that	O
they	O
inherited	O
.	O
</s>
<s>
The	O
Macintosh	B-Device
Quadra	I-Device
series	O
was	O
introduced	O
in	O
1991	O
with	O
a	O
new	O
PDS	O
for	O
the	O
Motorola	B-Device
68040	I-Device
processor	O
which	O
was	O
in-line	O
with	O
one	O
of	O
the	O
NuBus	B-Device
slots	O
.	O
</s>
<s>
The	O
Quadra	B-Device
605	I-Device
and	O
Quadra	B-Device
630	I-Device
were	O
exceptions	O
which	O
used	O
a	O
32-bit	O
version	O
of	O
the	O
LC	O
slot	O
.	O
</s>
<s>
Both	O
allowed	O
for	O
PowerPC	B-Architecture
upgrades	O
through	O
the	O
"	O
Ready	O
for	O
PowerPC	B-Architecture
upgrade	O
"	O
program	O
.	O
</s>
<s>
The	O
PowerBook	B-Device
Duo	I-Device
line	O
was	O
introduced	O
in	O
1992	O
with	O
a	O
unique	O
68030-based	O
connector	O
that	O
could	O
allow	O
the	O
subnotebook	O
logic	O
board	O
to	O
communicate	O
with	O
an	O
array	O
of	O
desktop	O
docking	O
systems	O
,	O
some	O
of	O
which	O
could	O
be	O
upgraded	O
with	O
floating-point	B-General_Concept
units	I-General_Concept
.	O
</s>
<s>
Because	O
of	O
the	O
complexity	O
of	O
larger	O
Duo	O
Docks	O
,	O
NuBus	B-Device
was	O
used	O
to	O
manage	O
parts	O
of	O
the	O
subsystems	O
.	O
</s>
<s>
First	O
generation	O
Power	B-Device
Macintosh	I-Device
systems	O
with	O
NuBus	B-Device
architecture	O
,	O
such	O
as	O
the	O
6100	B-Device
,	O
7100	B-Device
,	O
and	O
8100	B-Device
,	O
included	O
a	O
PDS	O
that	O
was	O
used	O
for	O
high-speed	O
AV	O
cards	O
.	O
</s>
<s>
It	O
was	O
later	O
used	O
by	O
third-party	O
manufacturers	O
to	O
support	O
PowerPC	B-Device
G3	I-Device
and	O
G4	B-General_Concept
upgrades	O
.	O
</s>
<s>
High-end	O
second	O
generation	O
Power	B-Device
Macintosh	I-Device
systems	O
with	O
PCI	B-Protocol
architecture	O
,	O
such	O
as	O
the	O
7500	B-Device
through	O
9600	B-Device
,	O
had	O
their	O
PowerPC	B-Architecture
601	O
and	O
604	O
processors	O
on	O
daughtercards	O
which	O
could	O
be	O
swapped	O
out	O
for	O
PowerPC	B-Device
G3	I-Device
and	O
G4	B-General_Concept
upgrades	O
.	O
</s>
<s>
Mid-range	O
Power	B-Device
Macintosh	I-Device
systems	O
based	O
on	O
PowerPC	B-Architecture
603e	O
processors	O
with	O
PCI	B-Protocol
architecture	O
,	O
such	O
as	O
the	O
5400	B-Device
,	O
5500	B-Device
,	O
and	O
6360	O
through	O
6500	B-Device
,	O
featured	O
an	O
L2	O
cache	B-General_Concept
slot	O
which	O
provided	O
direct	O
access	O
to	O
the	O
CPU	O
.	O
</s>
<s>
This	O
allowed	O
enterprising	O
third-party	O
manufacturers	O
to	O
build	O
PowerPC	B-Device
G3	I-Device
upgrades	O
for	O
this	O
slot	O
.	O
</s>
<s>
More	O
recent	O
Macs	O
have	O
such	O
high	O
processor	O
speeds	O
that	O
a	O
PDS	O
would	O
not	O
be	O
practical	O
and	O
instead	O
adopted	O
PCIe	O
and	O
Thunderbolt	B-Protocol
.	O
</s>
<s>
The	O
last	O
implementation	O
resembling	O
such	O
a	O
slot	O
by	O
Apple	O
is	O
the	O
processor	O
tray	O
connector	O
in	O
the	O
2009	O
to	O
2012	O
Mac	B-Device
Pros	I-Device
.	O
</s>
