<s>
The	O
Intel	B-General_Concept
386	I-General_Concept
,	O
originally	O
released	O
as	O
80386	B-General_Concept
and	O
later	O
renamed	O
i386	B-General_Concept
,	O
is	O
a	B-Application
32-bit	O
microprocessor	B-Architecture
introduced	O
in	O
1985	O
.	O
</s>
<s>
The	O
first	O
versions	O
had	O
275,000	O
transistors	B-Application
and	O
were	O
the	O
CPU	B-General_Concept
of	O
many	O
workstations	B-Device
and	O
high-end	O
personal	B-Device
computers	I-Device
of	O
the	O
time	O
.	O
</s>
<s>
As	O
the	O
original	O
implementation	O
of	O
the	O
32-bit	O
extension	O
of	O
the	O
80286	B-General_Concept
architecture	O
,	O
the	O
i386	B-General_Concept
instruction	O
set	O
,	O
programming	O
model	O
,	O
and	O
binary	O
encodings	O
are	O
still	O
the	O
common	O
denominator	O
for	O
all	O
32-bit	B-Device
x86	I-Device
processors	O
,	O
which	O
is	O
termed	O
the	O
i386	B-General_Concept
architecture	O
,	O
x86	B-Operating_System
,	O
or	O
IA-32	B-Device
,	O
depending	O
on	O
context	O
.	O
</s>
<s>
The	O
32-bit	O
i386	B-General_Concept
can	O
correctly	O
execute	O
most	O
code	O
intended	O
for	O
the	O
earlier	O
16-bit	B-Device
processors	I-Device
such	O
as	O
8086	B-General_Concept
and	O
80286	B-General_Concept
that	O
were	O
ubiquitous	O
in	O
early	O
PCs	B-Device
.	O
</s>
<s>
Over	O
the	O
years	O
,	O
successively	O
newer	O
implementations	O
of	O
the	O
same	O
architecture	O
have	O
become	O
several	O
hundreds	O
of	O
times	O
faster	O
than	O
the	O
original	O
80386	B-General_Concept
(	O
and	O
thousands	O
of	O
times	O
faster	O
than	O
the	O
8086	B-General_Concept
)	O
.	O
</s>
<s>
The	O
25	O
MHz	O
386	B-General_Concept
version	O
was	O
clocking	O
7	O
MIPS	O
.	O
</s>
<s>
A	B-Application
33MHz	O
80386	B-General_Concept
was	O
reportedly	O
measured	O
to	O
operate	O
at	O
about	O
11.4	O
MIPS	O
.	O
</s>
<s>
Development	O
of	O
i386	B-General_Concept
technology	O
began	O
in	O
1982	O
under	O
the	O
internal	O
name	O
of	O
P3	O
.	O
</s>
<s>
The	O
tape-out	O
of	O
the	O
80386	B-General_Concept
development	O
was	O
finalized	O
in	O
July	O
1985	O
.	O
</s>
<s>
The	O
80386	B-General_Concept
was	O
introduced	O
as	O
pre-production	O
samples	O
for	O
software	O
development	O
workstations	B-Device
in	O
October	O
1985	O
.	O
</s>
<s>
Manufacturing	O
of	O
the	O
chips	O
in	O
significant	O
quantities	O
commenced	O
in	O
June	O
1986	O
,	O
along	O
with	O
the	O
first	O
plug-in	O
device	O
that	O
allowed	O
existing	O
80286-based	O
computers	O
to	O
be	O
upgraded	O
to	O
the	O
386	B-General_Concept
,	O
the	O
Translator	O
386	B-General_Concept
by	O
American	O
Computer	O
and	O
Peripheral	O
.	O
</s>
<s>
Mainboards	B-Device
for	O
80386-based	O
computer	O
systems	O
were	O
cumbersome	O
and	O
expensive	O
at	O
first	O
,	O
but	O
manufacturing	O
was	O
justified	O
upon	O
the	O
80386	B-General_Concept
's	O
mainstream	O
adoption	O
.	O
</s>
<s>
The	O
first	O
personal	B-Device
computer	I-Device
to	O
make	O
use	O
of	O
the	O
80386	B-General_Concept
was	O
the	O
Deskpro	B-Device
386	I-Device
,	O
designed	O
and	O
manufactured	O
by	O
Compaq	O
;	O
this	O
marked	O
the	O
first	O
time	O
a	B-Application
fundamental	O
component	O
in	O
the	O
IBM	O
PC	B-Device
compatible	O
de	O
facto	O
standard	O
was	O
updated	O
by	O
a	B-Application
company	O
other	O
than	O
IBM	O
.	O
</s>
<s>
In	O
May	O
2006	O
,	O
Intel	O
announced	O
that	O
i386	B-General_Concept
production	O
would	O
stop	O
at	O
the	O
end	O
of	O
September	O
2007	O
.	O
</s>
<s>
Although	O
it	O
had	O
long	O
been	O
obsolete	O
as	O
a	B-Application
personal	B-Device
computer	I-Device
CPU	B-General_Concept
,	O
Intel	O
and	O
others	O
had	O
continued	O
making	O
the	O
chip	O
for	O
embedded	B-Architecture
systems	I-Architecture
.	O
</s>
<s>
Such	O
systems	O
using	O
an	O
i386	B-General_Concept
or	O
one	O
of	O
many	O
derivatives	O
are	O
common	O
in	O
aerospace	O
technology	O
and	O
electronic	O
musical	O
instruments	O
,	O
among	O
others	O
.	O
</s>
<s>
Some	O
mobile	O
phones	O
also	O
used	O
(	O
later	O
fully	O
static	O
CMOS	B-Device
variants	O
of	O
)	O
the	O
i386	B-General_Concept
processor	O
,	O
such	O
as	O
BlackBerry	B-Application
950	I-Application
and	O
Nokia	O
9000	O
Communicator	O
.	O
</s>
<s>
Linux	B-Operating_System
continued	O
to	O
support	O
i386	B-General_Concept
processors	O
until	O
December	O
11	O
,	O
2012	O
,	O
when	O
the	O
kernel	B-Operating_System
cut	O
386-specific	O
instructions	O
in	O
version	O
3.8	O
.	O
</s>
<s>
The	O
processor	O
was	O
a	B-Application
significant	O
evolution	O
in	O
the	O
x86	B-Operating_System
architecture	I-Operating_System
,	O
and	O
extended	O
a	B-Application
long	O
line	O
of	O
processors	O
that	O
stretched	O
back	O
to	O
the	O
Intel	B-General_Concept
8008	I-General_Concept
.	O
</s>
<s>
The	O
predecessor	O
of	O
the	O
80386	B-General_Concept
was	O
the	O
Intel	B-General_Concept
80286	I-General_Concept
,	O
a	B-Application
16-bit	B-Device
processor	I-Device
with	O
a	B-Application
segment-based	O
memory	B-General_Concept
management	I-General_Concept
and	O
protection	O
system	O
.	O
</s>
<s>
The	O
80386	B-General_Concept
added	O
a	B-Application
three-stage	O
instruction	O
pipeline	O
which	O
it	O
brings	O
up	O
to	O
total	O
of	O
6-stage	O
instruction	O
pipeline	O
,	O
extended	O
the	O
architecture	O
from	O
16-bits	B-Device
to	O
32-bits	O
,	O
and	O
added	O
an	O
on-chip	O
memory	B-General_Concept
management	I-General_Concept
unit	I-General_Concept
.	O
</s>
<s>
This	O
paging	B-Architecture
translation	O
unit	O
made	O
it	O
much	O
easier	O
to	O
implement	O
operating	O
systems	O
that	O
used	O
virtual	B-Architecture
memory	I-Architecture
.	O
</s>
<s>
It	O
also	O
offered	O
support	O
for	O
register	B-Device
debugging	I-Device
.	O
</s>
<s>
The	O
80386	B-General_Concept
featured	O
three	O
operating	O
modes	O
:	O
real	B-Application
mode	I-Application
,	O
protected	B-Application
mode	I-Application
and	O
virtual	O
mode	O
.	O
</s>
<s>
The	O
protected	B-Application
mode	I-Application
,	O
which	O
debuted	O
in	O
the	O
286	B-General_Concept
,	O
was	O
extended	O
to	O
allow	O
the	O
386	B-General_Concept
to	O
address	O
up	O
to	O
4	O
GB	O
of	O
memory	O
.	O
</s>
<s>
With	O
the	O
addition	O
of	O
segmented	B-General_Concept
addressing	I-General_Concept
system	O
,	O
it	O
can	O
expand	O
up	O
to	O
64	O
terabytes	O
of	O
virtual	B-Architecture
memory	I-Architecture
.	O
</s>
<s>
The	O
all	O
new	O
virtual	B-Application
8086	I-Application
mode	I-Application
(	O
or	O
VM86	B-Application
)	O
made	O
it	O
possible	O
to	O
run	O
one	O
or	O
more	O
real	B-Application
mode	I-Application
programs	O
in	O
a	B-Application
protected	O
environment	O
,	O
although	O
some	O
programs	O
were	O
not	O
compatible	O
.	O
</s>
<s>
The	O
ability	O
for	O
a	B-Application
386	B-General_Concept
to	O
be	O
set	O
up	O
to	O
act	O
like	O
it	O
had	O
a	B-Application
flat	B-General_Concept
memory	I-General_Concept
model	I-General_Concept
in	O
protected	B-Application
mode	I-Application
despite	O
the	O
fact	O
that	O
it	O
uses	O
a	B-Application
segmented	B-General_Concept
memory	I-General_Concept
model	O
in	O
all	O
modes	O
was	O
arguably	O
the	O
most	O
important	O
feature	O
change	O
for	O
the	O
x86	B-Operating_System
processor	O
family	O
until	O
AMD	O
released	O
x86-64	B-Device
in	O
2003	O
.	O
</s>
<s>
Several	O
new	O
instructions	O
have	O
been	O
added	O
to	O
386	B-General_Concept
:	O
BSF	O
,	O
BSR	O
,	O
BT	O
,	O
BTS	O
,	O
BTR	O
,	O
BTC	O
,	O
CDQ	O
,	O
CWDE	O
,	O
LFS	O
,	O
LGS	O
,	O
LSS	O
,	O
MOVSX	O
,	O
MOVZX	O
,	O
SETcc	O
,	O
SHLD	O
,	O
SHRD	O
.	O
</s>
<s>
Two	O
new	O
segment	B-General_Concept
registers	I-General_Concept
have	O
been	O
added	O
(	O
FS	O
and	O
GS	O
)	O
for	O
general-purpose	O
programs	O
,	O
single	O
Machine	O
Status	O
Word	O
of	O
286	B-General_Concept
grew	O
into	O
eight	O
control	B-Operating_System
registers	I-Operating_System
CR0	B-Operating_System
–	O
CR7	O
.	O
</s>
<s>
Debug	B-Device
registers	I-Device
DR0	O
–	O
DR7	O
were	O
added	O
for	O
hardware	O
breakpoints	O
.	O
</s>
<s>
Chief	O
architect	O
in	O
the	O
development	O
of	O
the	O
80386	B-General_Concept
was	O
John	O
H	O
.	O
Crawford	O
.	O
</s>
<s>
He	O
was	O
responsible	O
for	O
extending	O
the	O
80286	B-General_Concept
architecture	O
and	O
instruction	O
set	O
to	O
32-bit	O
,	O
and	O
then	O
led	O
the	O
microprogram	B-Device
development	O
for	O
the	O
80386	B-General_Concept
chip	O
.	O
</s>
<s>
The	O
i486	B-General_Concept
and	O
P5	B-General_Concept
Pentium	B-General_Concept
line	O
of	O
processors	O
were	O
descendants	O
of	O
the	O
i386	B-General_Concept
design	O
.	O
</s>
<s>
The	O
following	O
data	O
types	O
are	O
directly	O
supported	O
and	O
thus	O
implemented	O
by	O
one	O
or	O
more	O
i386	B-General_Concept
machine	B-Language
instructions	I-Language
;	O
these	O
data	O
types	O
are	O
briefly	O
described	O
here	O
.	O
</s>
<s>
16-bit	B-Device
integer	O
,	O
either	O
signed	O
(	O
range	O
−	O
32,768	O
32	O
..	O
,	O
767	O
)	O
or	O
unsigned	O
(	O
range	O
0	O
..	O
65	O
,	O
535	O
)	O
.	O
</s>
<s>
Offset	O
,	O
a	B-Application
16	O
-	O
or	O
32-bit	O
displacement	O
referring	O
to	O
a	B-Application
memory	O
location	O
(	O
using	O
any	O
addressing	O
mode	O
)	O
.	O
</s>
<s>
Pointer	O
,	O
a	B-Application
16-bit	B-Device
selector	O
together	O
with	O
a	B-Application
16	O
-	O
or	O
32-bit	O
offset	O
.	O
</s>
<s>
String	O
,	O
a	B-Application
sequence	O
of	O
8-	O
,	O
16	O
-	O
or	O
32-bit	O
words	O
(	O
up	O
to	O
4	O
Gbyte	O
in	O
length	O
)	O
.	O
</s>
<s>
The	O
following	O
i386	B-General_Concept
assembly	B-Language
source	O
code	O
is	O
for	O
a	B-Application
subroutine	O
named	O
_strtolower	O
that	O
copies	O
a	B-Application
null-terminated	O
ASCIIZ	B-Data_Structure
character	O
string	O
from	O
one	O
location	O
to	O
another	O
,	O
converting	O
all	O
alphabetic	O
characters	O
to	O
lower	O
case	O
.	O
</s>
<s>
The	O
string	O
is	O
copied	O
one	O
byte	O
(	O
8-bit	O
character	O
)	O
at	O
a	B-Application
time	O
.	O
</s>
<s>
cmp	O
al	O
,	O
'	O
A	B-Application
 '	O
;	O
If	O
AL	O
<	O
'	O
A	B-Application
 '	O
,	O
</s>
<s>
cmp	O
al	O
,	O
'	O
Z	B-Algorithm
 '	O
;	O
If	O
AL	O
>	O
'	O
Z	B-Algorithm
 '	O
,	O
</s>
<s>
The	O
example	O
code	O
uses	O
the	O
EBP	O
(	O
base	O
pointer	O
)	O
register	O
to	O
establish	O
a	B-Application
call	O
frame	O
,	O
an	O
area	O
on	O
the	O
stack	O
that	O
contains	O
all	O
of	O
the	O
parameters	O
and	O
local	O
variables	O
for	O
the	O
execution	O
of	O
the	O
subroutine	O
.	O
</s>
<s>
This	O
kind	O
of	O
calling	O
convention	O
supports	O
reentrant	B-Operating_System
and	O
recursive	O
code	O
and	O
has	O
been	O
used	O
by	O
Algol-like	O
languages	O
since	O
the	O
late	O
1950s	O
.	O
</s>
<s>
A	B-Application
flat	B-General_Concept
memory	I-General_Concept
model	I-General_Concept
is	O
assumed	O
,	O
specifically	O
,	O
that	O
the	O
DS	O
and	O
ES	O
segments	O
address	O
the	O
same	O
region	O
of	O
memory	O
.	O
</s>
<s>
The	O
80386SL	O
was	O
introduced	O
as	O
a	B-Application
power-efficient	O
version	O
for	O
laptop	B-Device
computers	I-Device
.	O
</s>
<s>
SMM	B-Architecture
)	O
,	O
as	O
well	O
as	O
different	O
"	O
sleep	O
"	O
modes	O
to	O
conserve	O
battery	O
power	O
.	O
</s>
<s>
It	O
also	O
contained	O
support	O
for	O
an	O
external	O
cache	B-General_Concept
of	O
16	O
to	O
64	O
KB	O
.	O
</s>
<s>
The	O
extra	O
functions	O
and	O
circuit	O
implementation	O
techniques	O
caused	O
this	O
variant	O
to	O
have	O
over	O
3	O
times	O
as	O
many	O
transistors	B-Application
as	O
the	O
i386DX	B-General_Concept
.	O
</s>
<s>
The	O
first	O
PC	B-Device
based	O
on	O
the	O
Intel	B-General_Concept
80386	I-General_Concept
was	O
the	O
Compaq	B-Device
Deskpro	I-Device
386	I-Device
.	O
</s>
<s>
By	O
extending	O
the	O
16/24	O
-bit	O
IBM	B-Operating_System
PC/AT	I-Operating_System
standard	O
into	O
a	B-Application
natively	O
32-bit	O
computing	O
environment	O
,	O
Compaq	O
became	O
the	O
first	O
company	O
to	O
design	O
and	O
manufacture	O
such	O
a	B-Application
major	O
technical	O
hardware	O
advance	O
on	O
the	O
PC	B-Device
platform	O
.	O
</s>
<s>
IBM	O
was	O
offered	O
use	O
of	O
the	O
80386	B-General_Concept
,	O
but	O
had	O
manufacturing	O
rights	O
for	O
the	O
earlier	O
80286	B-General_Concept
.	O
</s>
<s>
IBM	O
therefore	O
chose	O
to	O
rely	O
on	O
that	O
processor	O
for	O
a	B-Application
couple	O
more	O
years	O
.	O
</s>
<s>
The	O
early	O
success	O
of	O
the	O
Compaq	B-Device
Deskpro	I-Device
386	I-Device
played	O
an	O
important	O
role	O
in	O
legitimizing	O
the	O
PC	B-Device
"	O
clone	O
"	O
industry	O
and	O
in	O
de-emphasizing	O
IBM	O
's	O
role	O
within	O
it	O
.	O
</s>
<s>
The	O
first	O
computer	O
system	O
sold	O
with	O
the	O
386SX	O
was	O
the	O
Compaq	B-Device
Deskpro	I-Device
386S	I-Device
,	O
released	O
in	O
July	O
1988	O
.	O
</s>
<s>
Prior	O
to	O
the	O
386	B-General_Concept
,	O
the	O
difficulty	O
of	O
manufacturing	O
microchips	O
and	O
the	O
uncertainty	O
of	O
reliable	O
supply	O
made	O
it	O
desirable	O
that	O
any	O
mass-market	O
semiconductor	O
be	O
multi-sourced	O
,	O
that	O
is	O
,	O
made	O
by	O
two	O
or	O
more	O
manufacturers	O
,	O
the	O
second	O
and	O
subsequent	O
companies	O
manufacturing	O
under	O
license	O
from	O
the	O
originating	O
company	O
.	O
</s>
<s>
The	O
386	B-General_Concept
was	O
for	O
a	B-Application
time	O
(	O
4.7	O
years	O
)	O
only	O
available	O
from	O
Intel	O
,	O
since	O
Andy	O
Grove	O
,	O
Intel	O
's	O
CEO	O
at	O
the	O
time	O
,	O
made	O
the	O
decision	O
not	O
to	O
encourage	O
other	O
manufacturers	O
to	O
produce	O
the	O
processor	O
as	O
second	O
sources	O
.	O
</s>
<s>
This	O
decision	O
was	O
ultimately	O
crucial	O
to	O
Intel	O
's	O
success	O
in	O
the	O
market	O
.	O
</s>
<s>
The	O
386	B-General_Concept
was	O
the	O
first	O
significant	O
microprocessor	B-Architecture
to	O
be	O
single-sourced	B-Application
.	O
</s>
<s>
Single-sourcing	B-Application
the	O
386	B-General_Concept
allowed	O
Intel	O
greater	O
control	O
over	O
its	O
development	O
and	O
substantially	O
greater	O
profits	O
in	O
later	O
years	O
.	O
</s>
<s>
AMD	O
introduced	O
its	O
compatible	O
Am386	B-Device
processor	O
in	O
March	O
1991	O
after	O
overcoming	O
legal	O
obstacles	O
,	O
thus	O
ending	O
Intel	O
's	O
4.7-year	O
monopoly	O
on	O
386-compatible	O
processors	O
.	O
</s>
<s>
From	O
1991	O
IBM	O
also	O
manufactured	O
386	B-General_Concept
chips	O
under	O
license	O
for	O
use	O
only	O
in	O
IBM	O
PCs	B-Device
and	O
boards	O
.	O
</s>
<s>
The	O
AMD	O
Am386SX	O
and	O
Am386DX	O
were	O
almost	O
exact	O
clones	O
of	O
the	O
i386SX	O
and	O
i386DX	B-General_Concept
.	O
</s>
<s>
Legal	O
disputes	O
caused	O
production	O
delays	O
for	O
several	O
years	O
,	O
but	O
AMD	O
's	O
40MHz	O
part	O
eventually	O
became	O
very	O
popular	O
with	O
computer	O
enthusiasts	O
as	O
a	B-Application
low-cost	O
and	O
low-power	O
alternative	O
to	O
the	O
25MHz	O
486SX	O
.	O
</s>
<s>
The	O
power	O
draw	O
was	O
further	O
reduced	O
in	O
the	O
"	O
notebook	B-Device
models	O
"	O
(	O
Am386	B-Device
DXL/SXL/DXLV/SXLV	O
)	O
,	O
which	O
could	O
operate	O
with	O
3.3V	O
and	O
were	O
implemented	O
in	O
fully	O
static	O
CMOS	B-Device
circuitry	O
.	O
</s>
<s>
Cyrix	O
Cx486SLC/Cx486DLC	O
could	O
be	O
(	O
simplistically	O
)	O
described	O
as	O
a	B-Application
kind	O
of	O
386/486	O
hybrid	O
chip	O
that	O
included	O
a	B-Application
small	O
amount	O
of	O
on-chip	B-General_Concept
cache	I-General_Concept
.	O
</s>
<s>
The	O
Cyrix	B-Device
Cx486SLC	I-Device
and	O
Cyrix	B-Device
Cx486DLC	I-Device
processors	O
were	O
pin-compatible	O
with	O
i386SX	O
and	O
i386DX	B-General_Concept
respectively	O
.	O
</s>
<s>
IBM	B-Device
386SLC	I-Device
and	O
486SLC/DLC	O
were	O
variants	O
of	O
Intel	O
's	O
design	O
which	O
contained	O
a	B-Application
large	O
amount	O
of	O
on-chip	B-General_Concept
cache	I-General_Concept
(	O
8	O
KB	O
,	O
and	O
later	O
16	O
KB	O
)	O
.	O
</s>
<s>
The	O
agreement	O
with	O
Intel	O
limited	O
their	O
use	O
to	O
IBM	O
's	O
own	O
line	O
of	O
computers	O
and	O
upgrade	O
boards	O
only	O
,	O
so	O
they	O
were	O
not	O
available	O
on	O
the	O
open	O
market	O
.	O
</s>
<s>
Intel	O
originally	O
intended	O
for	O
the	O
80386	B-General_Concept
to	O
debut	O
at	O
16MHz	O
.	O
</s>
<s>
Early	O
in	O
production	O
,	O
Intel	O
discovered	O
a	B-Application
marginal	O
circuit	O
that	O
could	O
cause	O
a	B-Application
system	O
to	O
return	O
incorrect	O
results	O
from	O
32-bit	O
multiply	O
operations	O
.	O
</s>
<s>
Processors	O
that	O
were	O
found	O
to	O
be	O
bug-free	O
were	O
marked	O
with	O
a	B-Application
double	O
sigma	B-Application
( ΣΣ	O
)	O
,	O
and	O
affected	O
processors	O
were	O
marked	O
"	O
16	B-Device
BIT	I-Device
S/W	O
ONLY	O
"	O
.	O
</s>
<s>
The	O
i387	O
math	B-General_Concept
coprocessor	I-General_Concept
was	O
not	O
ready	O
in	O
time	O
for	O
the	O
introduction	O
of	O
the	O
80386	B-General_Concept
,	O
and	O
so	O
many	O
of	O
the	O
early	O
80386	B-General_Concept
motherboards	B-Device
instead	O
provided	O
a	B-Application
socket	O
and	O
hardware	O
logic	O
to	O
make	O
use	O
of	O
an	O
80287	O
.	O
</s>
<s>
In	O
this	O
configuration	O
the	O
FPU	B-General_Concept
operated	O
asynchronously	O
to	O
the	O
CPU	B-General_Concept
,	O
usually	O
with	O
a	B-Application
clock	O
rate	O
of	O
10MHz	O
.	O
</s>
<s>
The	O
original	O
Compaq	B-Device
Deskpro	I-Device
386	I-Device
is	O
an	O
example	O
of	O
such	O
design	O
.	O
</s>
<s>
However	O
,	O
this	O
was	O
an	O
annoyance	O
to	O
those	O
who	O
depended	O
on	O
floating-point	B-Algorithm
performance	O
,	O
as	O
the	O
performance	O
advantages	O
of	O
the	O
80387	O
over	O
the	O
80287	O
were	O
significant	O
.	O
</s>
<s>
Intel	O
later	O
offered	O
a	B-Application
modified	O
version	O
of	O
its	O
486DX	B-General_Concept
in	O
i386	B-General_Concept
packaging	O
,	O
branded	O
as	O
the	O
Intel	O
RapidCAD	B-Device
.	O
</s>
<s>
This	O
provided	O
an	O
upgrade	O
path	O
for	O
users	O
with	O
i386-compatible	O
hardware	O
.	O
</s>
<s>
The	O
upgrade	O
was	O
a	B-Application
pair	O
of	O
chips	O
that	O
replaced	O
both	O
the	O
i386	B-General_Concept
and	O
i387	O
.	O
</s>
<s>
Since	O
the	O
486DX	B-General_Concept
design	O
contained	O
an	O
FPU	B-General_Concept
,	O
the	O
chip	O
that	O
replaced	O
the	O
i386	B-General_Concept
contained	O
the	O
floating-point	B-Algorithm
functionality	O
,	O
and	O
the	O
chip	O
that	O
replaced	O
the	O
i387	O
served	O
very	O
little	O
purpose	O
.	O
</s>
<s>
However	O
,	O
the	O
latter	O
chip	O
was	O
necessary	O
in	O
order	O
to	O
provide	O
the	O
FERR	O
signal	O
to	O
the	O
mainboard	B-Device
and	O
appear	O
to	O
function	O
as	O
a	B-Application
normal	O
floating-point	B-General_Concept
unit	I-General_Concept
.	O
</s>
<s>
Third	O
parties	O
offered	O
a	B-Application
wide	O
range	O
of	O
upgrades	O
,	O
for	O
both	O
SX	O
and	O
DX	O
systems	O
.	O
</s>
<s>
The	O
most	O
popular	O
ones	O
were	O
based	O
on	O
the	O
Cyrix	O
486DLC/SLC	O
core	O
,	O
which	O
typically	O
offered	O
a	B-Application
substantial	O
speed	O
improvement	O
due	O
to	O
its	O
more	O
efficient	O
instruction	O
pipeline	O
and	O
internal	O
L1	O
SRAM	O
cache	B-General_Concept
.	O
</s>
<s>
The	O
cache	B-General_Concept
was	O
usually	O
1	O
KB	O
,	O
or	O
sometimes	O
8	O
KB	O
in	O
the	O
TI	O
variant	O
.	O
</s>
<s>
Some	O
of	O
the	O
fastest	O
CPU	B-General_Concept
upgrade	O
modules	O
featured	O
the	O
IBM	O
SLC/DLC	O
family	O
(	O
notable	O
for	O
its	O
16	O
KB	O
L1	O
cache	B-General_Concept
)	O
,	O
or	O
even	O
the	O
Intel	B-General_Concept
486	I-General_Concept
itself	O
.	O
</s>
<s>
Many	O
386	B-General_Concept
upgrade	O
kits	O
were	O
advertised	O
as	O
being	O
simple	O
drop-in	O
replacements	O
,	O
but	O
often	O
required	O
complicated	O
software	O
to	O
control	O
the	O
cache	B-General_Concept
or	O
clock	O
doubling	O
.	O
</s>
<s>
Part	O
of	O
the	O
problem	O
was	O
that	O
on	O
most	O
386	B-General_Concept
motherboards	B-Device
,	O
the	O
A20	B-Device
line	I-Device
was	O
controlled	O
entirely	O
by	O
the	O
motherboard	B-Device
with	O
the	O
CPU	B-General_Concept
being	O
unaware	O
,	O
which	O
caused	O
problems	O
on	O
CPUs	O
with	O
internal	B-General_Concept
caches	I-General_Concept
.	O
</s>
<s>
In	O
1988	O
,	O
Intel	O
introduced	O
the	O
80386SX	O
,	O
most	O
often	O
referred	O
to	O
as	O
the	O
386SX	O
,	O
a	B-Application
cut-down	O
version	O
of	O
the	O
80386	B-General_Concept
with	O
a	B-Application
16-bit	B-Device
data	O
bus	O
,	O
mainly	O
intended	O
for	O
lower-cost	O
PCs	B-Device
aimed	O
at	O
the	O
home	O
,	O
educational	O
,	O
and	O
small-business	O
markets	O
,	O
while	O
the	O
386DX	B-General_Concept
remained	O
the	O
high-end	O
variant	O
used	O
in	O
workstations	B-Device
,	O
servers	O
,	O
and	O
other	O
demanding	O
tasks	O
.	O
</s>
<s>
The	O
CPU	B-General_Concept
remained	O
fully	O
32-bit	O
internally	O
,	O
but	O
the	O
16-bit	B-Device
bus	O
was	O
intended	O
to	O
simplify	O
circuit-board	O
layout	O
and	O
reduce	O
total	O
cost	O
.	O
</s>
<s>
The	O
16-bit	B-Device
bus	O
simplified	O
designs	O
but	O
hampered	O
performance	O
.	O
</s>
<s>
Only	O
24	O
pins	O
were	O
connected	O
to	O
the	O
address	O
bus	O
,	O
therefore	O
limiting	O
addressing	O
to	O
16MB	O
,	O
but	O
this	O
was	O
not	O
a	B-Application
critical	O
constraint	O
at	O
the	O
time	O
.	O
</s>
<s>
Performance	O
differences	O
were	O
due	O
not	O
only	O
to	O
differing	O
data-bus	O
widths	O
,	O
but	O
also	O
due	O
to	O
performance-enhancing	O
cache	B-General_Concept
memories	I-General_Concept
often	O
employed	O
on	O
boards	O
using	O
the	O
original	O
chip	O
.	O
</s>
<s>
The	O
original	O
80386	B-General_Concept
was	O
subsequently	O
renamed	O
i386DX	B-General_Concept
to	O
avoid	O
confusion	O
.	O
</s>
<s>
However	O
,	O
Intel	O
subsequently	O
used	O
the	O
"	O
DX	O
"	O
suffix	O
to	O
refer	O
to	O
the	O
floating-point	B-Algorithm
capability	O
of	O
the	O
i486DX	B-General_Concept
.	O
</s>
<s>
The	O
387SX	O
was	O
an	O
80387	O
part	O
that	O
was	O
compatible	O
with	O
the	O
386SX	O
(	O
i.e.	O
</s>
<s>
with	O
a	B-Application
16-bit	B-Device
databus	O
)	O
.	O
</s>
<s>
The	O
386SX	O
was	O
packaged	O
in	O
a	B-Application
surface-mount	O
QFP	B-Algorithm
and	O
sometimes	O
offered	O
in	O
a	B-Application
socket	O
to	O
allow	O
for	O
an	O
upgrade	O
.	O
</s>
<s>
A	B-Application
specially	O
packaged	O
Intel	O
486DX	B-General_Concept
and	O
a	B-Application
dummy	O
floating-point	B-General_Concept
unit	I-General_Concept
(	O
FPU	B-General_Concept
)	O
designed	O
as	O
pin-compatible	O
replacements	O
for	O
an	O
i386	B-General_Concept
processor	O
and	O
i387	O
FPU	B-General_Concept
.	O
</s>
<s>
This	O
was	O
an	O
embedded	O
version	O
of	O
the	O
80386SX	O
which	O
did	O
not	O
support	O
real	B-Application
mode	I-Application
and	O
paging	B-Architecture
in	O
the	O
MMU	B-General_Concept
.	O
</s>
<s>
Usable	O
with	O
80387SX	B-Device
or	O
i387SL	O
FPUs	O
.	O
</s>
<s>
Transparent	O
power	O
management	O
mode	O
,	O
integrated	O
MMU	B-General_Concept
and	O
TTL	O
compatible	O
inputs	O
(	O
only	O
386SXSA	O
)	O
.	O
</s>
<s>
Transparent	O
power	O
management	O
mode	O
and	O
integrated	O
MMU	B-General_Concept
.	O
</s>
<s>
Windows	B-Application
95	I-Application
was	O
the	O
only	O
entry	O
in	O
the	O
Windows	O
9x	O
series	O
to	O
officially	O
support	O
the	O
386	B-General_Concept
,	O
requiring	O
at	O
least	O
a	B-Application
386DX	B-General_Concept
,	O
though	O
a	B-Application
486	B-General_Concept
or	O
better	O
was	O
recommended	O
;	O
Windows	B-Device
98	I-Device
requires	O
a	B-Application
486DX	B-General_Concept
or	O
higher	O
.	O
</s>
<s>
In	O
the	O
Windows	B-Device
NT	I-Device
family	I-Device
,	O
Windows	B-Device
NT	I-Device
3.51	I-Device
was	O
the	O
last	O
version	O
with	O
386	B-General_Concept
support	O
.	O
</s>
<s>
Debian	O
GNU/Linux	B-Application
removed	O
386	B-General_Concept
support	O
with	O
the	O
release	O
of	O
3.1	O
(	O
Sarge	O
)	O
in	O
2005	O
.	O
</s>
<s>
Citing	O
the	O
maintenance	O
burden	O
around	O
SMP	B-Operating_System
primitives	O
,	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
developers	O
cut	O
support	O
from	O
the	O
development	O
codebase	O
in	O
December	O
2012	O
,	O
later	O
released	O
as	O
kernel	B-Operating_System
version	O
3.8	O
.	O
</s>
<s>
Among	O
the	O
BSDs	B-Operating_System
,	O
FreeBSD	B-Operating_System
's	O
5.x	O
releases	O
were	O
the	O
last	O
to	O
support	O
the	O
386	B-General_Concept
;	O
support	O
for	O
the	O
386SX	O
was	O
cut	O
with	O
release	O
5.2	O
,	O
while	O
the	O
remaining	O
386	B-General_Concept
support	O
was	O
removed	O
with	O
the	O
6.0	O
release	O
in	O
2005	O
.	O
</s>
<s>
OpenBSD	B-Operating_System
removed	O
386	B-General_Concept
support	O
with	O
version	O
4.2	O
(	O
2007	O
)	O
,	O
DragonFly	B-Application
BSD	I-Application
with	O
release	O
1.12	O
(	O
2008	O
)	O
,	O
and	O
NetBSD	B-Device
with	O
the	O
5.0	O
release	O
(	O
2009	O
)	O
.	O
</s>
