<s>
A	O
SIMM	B-General_Concept
(	O
single	B-General_Concept
in-line	I-General_Concept
memory	I-General_Concept
module	I-General_Concept
)	O
is	O
a	O
type	O
of	O
memory	B-General_Concept
module	I-General_Concept
containing	O
random-access	B-Architecture
memory	I-Architecture
used	O
in	O
computers	O
from	O
the	O
early	O
1980s	O
to	O
the	O
early	O
2000s	O
.	O
</s>
<s>
It	O
differs	O
from	O
a	O
dual	B-General_Concept
in-line	I-General_Concept
memory	I-General_Concept
module	I-General_Concept
(	O
DIMM	B-General_Concept
)	O
,	O
the	O
most	O
predominant	O
form	O
of	O
memory	B-General_Concept
module	I-General_Concept
since	O
the	O
late	O
1990s	O
,	O
in	O
that	O
the	O
contacts	O
on	O
a	O
SIMM	B-General_Concept
are	O
redundant	O
on	O
both	O
sides	O
of	O
the	O
module	O
.	O
</s>
<s>
SIMMs	B-General_Concept
were	O
standardised	O
under	O
the	O
JEDEC	O
JESD-21C	O
standard	O
.	O
</s>
<s>
Most	O
early	O
PC	B-Device
motherboards	I-Device
(	O
8088-based	O
PCs	O
,	O
XTs	O
,	O
and	O
early	O
ATs	B-Operating_System
)	O
used	O
socketed	O
DIP	B-Algorithm
chips	O
for	O
DRAM	O
.	O
</s>
<s>
As	O
computer	O
memory	O
capacities	O
grew	O
,	O
memory	B-General_Concept
modules	I-General_Concept
were	O
used	O
to	O
save	O
motherboard	B-Device
space	O
and	O
ease	O
memory	O
expansion	O
.	O
</s>
<s>
Instead	O
of	O
plugging	O
in	O
eight	O
or	O
nine	O
single	O
DIP	B-Algorithm
chips	O
,	O
only	O
one	O
additional	O
memory	B-General_Concept
module	I-General_Concept
was	O
needed	O
to	O
increase	O
the	O
memory	O
of	O
the	O
computer	O
.	O
</s>
<s>
SIMMs	B-General_Concept
were	O
invented	O
in	O
1982	O
by	O
James	O
J	O
.	O
Parker	O
at	O
Zenith	O
Microcircuits	O
and	O
the	O
first	O
Zenith	O
Microcircuits	O
customer	O
was	O
Wang	O
Laboratories	O
.	O
</s>
<s>
The	O
original	O
memory	B-General_Concept
modules	I-General_Concept
were	O
built	O
upon	O
ceramic	O
substrates	O
with	O
64K	O
Hitachi	O
"	O
flip	O
chip	O
"	O
parts	O
and	O
had	O
pins	O
,	O
i.e.	O
</s>
<s>
single	O
in-line	O
package	O
(	O
SIP	O
)	O
packaging	B-Algorithm
.	O
</s>
<s>
SIMMs	B-General_Concept
using	O
pins	O
are	O
usually	O
called	O
SIP	B-General_Concept
or	I-General_Concept
SIPP	I-General_Concept
memory	I-General_Concept
modules	O
to	O
distinguish	O
them	O
from	O
the	O
more	O
common	O
modules	O
using	O
edge	O
connectors	O
.	O
</s>
<s>
The	O
first	O
variant	O
of	O
SIMMs	B-General_Concept
has	O
30	O
pins	O
and	O
provides	O
8	O
bits	O
of	O
data	O
(	O
plus	O
a	O
9th	O
error-detection	O
bit	O
in	O
parity	B-Error_Name
SIMMs	B-General_Concept
)	O
.	O
</s>
<s>
They	O
were	O
used	O
in	O
AT-compatible	O
(	O
286-based	O
,	O
e.g.	O
,	O
Wang	O
APC	O
)	O
,	O
386-based	O
,	O
486-based	O
,	O
Macintosh	B-Device
Plus	I-Device
,	O
Macintosh	B-Device
II	I-Device
,	O
Quadra	B-Device
,	O
Atari	O
STE	O
microcomputers	O
,	O
Wang	O
VS	O
minicomputers	O
and	O
Roland	O
electronic	O
samplers	O
.	O
</s>
<s>
The	O
second	O
variant	O
of	O
SIMMs	B-General_Concept
has	O
72	O
pins	O
and	O
provides	O
32	O
bits	O
of	O
data	O
(	O
36	O
bits	O
in	O
parity	B-Error_Name
and	O
ECC	B-General_Concept
versions	O
)	O
.	O
</s>
<s>
These	O
appeared	O
first	O
in	O
the	O
early	O
1990s	O
in	O
later	O
models	O
of	O
the	O
IBM	B-Device
PS/2	I-Device
,	O
and	O
later	O
in	O
systems	O
based	O
on	O
the	O
486	B-General_Concept
,	O
Pentium	B-General_Concept
,	O
Pentium	B-Device
Pro	I-Device
,	O
early	O
Pentium	B-General_Concept
II	I-General_Concept
,	O
and	O
contemporary/competing	O
chips	O
of	O
other	O
brands	O
.	O
</s>
<s>
By	O
the	O
mid-90s	O
,	O
72-pin	O
SIMMs	B-General_Concept
had	O
replaced	O
30-pin	O
SIMMs	B-General_Concept
in	O
new-build	O
computers	O
,	O
and	O
were	O
starting	O
to	O
themselves	O
be	O
replaced	O
by	O
DIMMs	B-General_Concept
.	O
</s>
<s>
Non-IBM	O
PC	O
computers	O
such	O
as	O
UNIX	B-Device
workstations	I-Device
may	O
use	O
proprietary	O
non-standard	O
SIMMs	B-General_Concept
.	O
</s>
<s>
The	O
Macintosh	B-Device
IIfx	I-Device
uses	O
proprietary	O
non-standard	O
SIMMs	B-General_Concept
with	O
64	O
pins	O
.	O
</s>
<s>
DRAM	O
technologies	O
used	O
in	O
SIMMs	B-General_Concept
include	O
FPM	O
(	O
Fast	O
Page	O
Mode	O
memory	O
,	O
used	O
in	O
all	O
30-pin	O
and	O
early	O
72-pin	O
modules	O
)	O
,	O
and	O
the	O
higher-performance	O
EDO	O
DRAM	O
(	O
used	O
in	O
later	O
72-pin	O
modules	O
)	O
.	O
</s>
<s>
Due	O
to	O
the	O
differing	O
data	O
bus	O
widths	O
of	O
the	O
memory	B-General_Concept
modules	I-General_Concept
and	O
some	O
processors	O
,	O
sometimes	O
several	O
modules	O
must	O
be	O
installed	O
in	O
identical	O
pairs	O
or	O
in	O
identical	O
groups	O
of	O
four	O
to	O
fill	O
a	O
memory	O
bank	O
.	O
</s>
<s>
The	O
rule	O
of	O
thumb	O
is	O
a	O
286	B-General_Concept
,	O
386SX	O
,	O
68000	B-Device
or	O
low-end	O
68020	B-Device
/	O
68030	B-Device
(	O
e.g.	O
</s>
<s>
Atari	O
Falcon	O
,	O
Mac	O
LC	O
)	O
system	O
(	O
using	O
a	O
16	O
bit	O
wide	O
data	O
bus	O
)	O
would	O
require	O
two	O
30-pin	O
SIMMs	B-General_Concept
for	O
a	O
memory	O
bank	O
.	O
</s>
<s>
On	O
386DX	B-General_Concept
,	O
486	B-General_Concept
,	O
and	O
full-spec	O
68020	B-Device
through	O
68060	B-General_Concept
(	O
e.g.	O
</s>
<s>
Atari	O
TT	O
,	O
Amiga	B-Device
4000	O
,	O
Mac	B-Device
II	I-Device
)	O
systems	O
(	O
32	O
bit	O
data	O
bus	O
)	O
,	O
either	O
four	O
30-pin	O
SIMMs	B-General_Concept
or	O
one	O
72-pin	O
SIMM	B-General_Concept
are	O
required	O
for	O
one	O
memory	O
bank	O
.	O
</s>
<s>
On	O
Pentium	B-General_Concept
systems	O
(	O
data	O
bus	O
width	O
of	O
64	O
bits	O
)	O
,	O
two	O
72-pin	O
SIMMs	B-General_Concept
are	O
required	O
.	O
</s>
<s>
However	O
,	O
some	O
Pentium	B-General_Concept
systems	O
have	O
support	O
for	O
a	O
"	O
half	O
bank	O
mode	O
"	O
,	O
in	O
which	O
the	O
data	O
bus	O
would	O
be	O
shortened	O
to	O
only	O
32	O
bits	O
to	O
allow	O
operation	O
of	O
a	O
single	O
SIMM	B-General_Concept
.	O
</s>
<s>
Conversely	O
,	O
some	O
386	B-General_Concept
and	O
486	B-General_Concept
systems	O
use	O
what	O
is	O
known	O
as	O
"	O
memory	O
interleaving	O
"	O
,	O
which	O
requires	O
twice	O
as	O
many	O
SIMMs	B-General_Concept
and	O
effectively	O
doubles	O
the	O
bandwidth	O
.	O
</s>
<s>
The	O
earliest	O
SIMM	B-General_Concept
sockets	O
were	O
conventional	O
push-type	O
sockets	O
.	O
</s>
<s>
These	O
were	O
soon	O
replaced	O
by	O
ZIF	B-General_Concept
sockets	I-General_Concept
in	O
which	O
the	O
SIMM	B-General_Concept
was	O
inserted	O
at	O
an	O
angle	O
,	O
then	O
tilted	O
into	O
an	O
upright	O
position	O
.	O
</s>
<s>
To	O
remove	O
one	O
,	O
the	O
two	O
metal	O
or	O
plastic	O
clips	O
at	O
each	O
end	O
must	O
be	O
pulled	O
to	O
the	O
side	O
,	O
then	O
the	O
SIMM	B-General_Concept
must	O
be	O
tilted	O
back	O
and	O
pulled	O
out	O
(	O
low-profile	O
sockets	O
reversed	O
this	O
convention	O
somewhat	O
,	O
like	O
SODIMMs	B-General_Concept
-	O
the	O
modules	O
are	O
inserted	O
at	O
a	O
"	O
high	O
"	O
angle	O
,	O
then	O
pushed	O
down	O
to	O
become	O
more	O
flush	O
with	O
the	O
motherboard	B-Device
)	O
.	O
</s>
<s>
Some	O
SIMMs	B-General_Concept
support	O
presence	B-General_Concept
detect	I-General_Concept
(	O
PD	O
)	O
.	O
</s>
<s>
Connections	O
are	O
made	O
to	O
some	O
of	O
the	O
pins	O
that	O
encode	O
the	O
capacity	O
and	O
speed	O
of	O
the	O
SIMM	B-General_Concept
,	O
so	O
that	O
compatible	O
equipment	O
can	O
detect	O
the	O
properties	O
of	O
the	O
SIMM	B-General_Concept
.	O
</s>
<s>
PD	O
SIMMs	B-General_Concept
can	O
be	O
used	O
in	O
equipment	O
which	O
does	O
not	O
support	O
PD	O
;	O
the	O
information	O
is	O
ignored	O
.	O
</s>
<s>
Standard	O
SIMMs	B-General_Concept
can	O
easily	O
be	O
converted	O
to	O
support	O
PD	O
by	O
fitting	O
jumpers	O
,	O
if	O
the	O
SIMMs	B-General_Concept
have	O
solder	O
pads	O
to	O
do	O
so	O
,	O
or	O
by	O
soldering	O
wires	O
on	O
.	O
</s>
<s>
30-pin	O
SIMMS	B-General_Concept
have	O
12	O
address	O
lines	O
,	O
which	O
can	O
provide	O
a	O
total	O
of	O
24	O
address	O
bits	O
.	O
</s>
<s>
With	O
an	O
8	O
bit	O
data	O
width	O
,	O
this	O
leads	O
to	O
an	O
absolute	O
maximum	O
capacity	O
of	O
16	O
MB	O
for	O
both	O
parity	B-Error_Name
and	O
non-parity	O
modules	O
(	O
the	O
additional	O
redundancy	O
bit	O
chip	O
usually	O
does	O
not	O
contribute	O
to	O
the	O
usable	O
capacity	O
)	O
.	O
</s>
<s>
*	O
Pins	O
26	O
,	O
28	O
and	O
29	O
are	O
not	O
connected	O
on	O
non-parity	O
SIMMs	B-General_Concept
.	O
</s>
<s>
*	O
Pins	O
35	O
,	O
36	O
,	O
37	O
and	O
38	O
are	O
not	O
connected	O
on	O
non-parity	O
SIMMs	B-General_Concept
.	O
</s>
<s>
†	O
/RAS1	O
and	O
/RAS3	O
are	O
only	O
used	O
on	O
two-rank	O
SIMMS	B-General_Concept
:	O
2	O
,	O
8	O
,	O
32	O
,	O
and	O
128	O
MB	O
.	O
</s>
<s>
x	O
Presence	B-General_Concept
Detect	I-General_Concept
signals	O
are	O
detailed	O
in	O
JEDEC	O
Standard	O
.	O
</s>
<s>
Several	O
CPU	O
cards	O
from	O
Great	B-Device
Valley	I-Device
Products	I-Device
for	O
the	O
Commodore	B-Device
Amiga	I-Device
used	O
special	O
64-pin	O
SIMMs	B-General_Concept
(	O
32	O
bits	O
wide	O
,	O
1	O
,	O
4	O
or	O
16	O
MB	O
,	O
60	O
ns	O
)	O
.	O
</s>
<s>
Dual-ported	B-General_Concept
64-pin	O
SIMMs	B-General_Concept
were	O
used	O
in	O
Apple	O
Macintosh	B-Device
IIfx	I-Device
computers	O
to	O
allow	O
overlapping	O
read/write	O
cycles	O
(	O
1	O
,	O
4	O
,	O
8	O
,	O
16	O
MB	O
,	O
80	O
ns	O
)	O
.	O
</s>
<s>
72-pin	O
SIMMs	B-General_Concept
with	O
non-standard	O
Presence	B-General_Concept
Detect	I-General_Concept
(	O
PD	O
)	O
connections	O
.	O
</s>
