<s>
x87	B-Application
is	O
a	O
floating-point-related	O
subset	O
of	O
the	O
x86	B-Operating_System
architecture	I-Operating_System
instruction	B-General_Concept
set	I-General_Concept
.	O
</s>
<s>
It	O
originated	O
as	O
an	O
extension	O
of	O
the	O
8086	B-General_Concept
instruction	B-General_Concept
set	I-General_Concept
in	O
the	O
form	O
of	O
optional	O
floating-point	B-Algorithm
coprocessors	B-General_Concept
that	O
worked	O
in	O
tandem	O
with	O
corresponding	O
x86	B-Operating_System
CPUs	O
.	O
</s>
<s>
This	O
was	O
also	O
known	O
as	O
the	O
NPX	B-Application
(	O
Numeric	B-Application
Processor	I-Application
eXtension	I-Application
)	O
.	O
</s>
<s>
Like	O
other	O
extensions	O
to	O
the	O
basic	O
instruction	B-General_Concept
set	I-General_Concept
,	O
x87	B-Application
instructions	O
are	O
not	O
strictly	O
needed	O
to	O
construct	O
working	O
programs	O
,	O
but	O
provide	O
hardware	O
and	O
microcode	B-Device
implementations	O
of	O
common	O
numerical	O
tasks	O
,	O
allowing	O
these	O
tasks	O
to	O
be	O
performed	O
much	O
faster	O
than	O
corresponding	O
machine	B-Language
code	I-Language
routines	O
can	O
.	O
</s>
<s>
The	O
x87	B-Application
instruction	B-General_Concept
set	I-General_Concept
includes	O
instructions	O
for	O
basic	O
floating-point	B-Algorithm
operations	O
such	O
as	O
addition	O
,	O
subtraction	O
and	O
comparison	O
,	O
but	O
also	O
for	O
more	O
complex	O
numerical	O
operations	O
,	O
such	O
as	O
the	O
computation	O
of	O
the	O
tangent	O
function	O
and	O
its	O
inverse	O
,	O
for	O
example	O
.	O
</s>
<s>
Most	O
x86	B-Operating_System
processors	O
since	O
the	O
Intel	B-General_Concept
80486	I-General_Concept
have	O
had	O
these	O
x87	B-Application
instructions	O
implemented	O
in	O
the	O
main	O
CPU	O
,	O
but	O
the	O
term	O
is	O
sometimes	O
still	O
used	O
to	O
refer	O
to	O
that	O
part	O
of	O
the	O
instruction	B-General_Concept
set	I-General_Concept
.	O
</s>
<s>
Before	O
x87	B-Application
instructions	O
were	O
standard	O
in	O
PCs	O
,	O
compilers	B-Language
or	O
programmers	O
had	O
to	O
use	O
rather	O
slow	O
library	O
calls	O
to	O
perform	O
floating-point	B-Algorithm
operations	O
,	O
a	O
method	O
that	O
is	O
still	O
common	O
in	O
(	O
low-cost	O
)	O
embedded	B-Architecture
systems	I-Architecture
.	O
</s>
<s>
The	O
x87	B-Application
registers	O
form	O
an	O
eight-level	O
deep	O
non-strict	O
stack	B-Application
structure	O
ranging	O
from	O
ST(0 )	O
to	O
ST(7 )	O
with	O
registers	O
that	O
can	O
be	O
directly	O
accessed	O
by	O
either	O
operand	O
,	O
using	O
an	O
offset	O
relative	O
to	O
the	O
top	O
,	O
as	O
well	O
as	O
pushed	O
and	O
popped	O
.	O
</s>
<s>
(	O
This	O
scheme	O
may	O
be	O
compared	O
to	O
how	O
a	O
stack	B-Application
frame	O
may	O
be	O
both	O
pushed/popped	O
and	O
indexed	O
.	O
)	O
</s>
<s>
There	O
are	O
instructions	O
to	O
push	O
,	O
calculate	O
,	O
and	O
pop	O
values	O
on	O
top	O
of	O
this	O
stack	B-Application
;	O
unary	O
operations	O
(	O
FSQRT	O
,	O
FPTAN	O
etc	O
.	O
)	O
</s>
<s>
The	O
non-strict	O
stack	B-Application
model	O
also	O
allows	O
binary	O
operations	O
to	O
use	O
ST(0 )	O
together	O
with	O
a	O
direct	O
memory	O
operand	O
or	O
with	O
an	O
explicitly	O
specified	O
stack	B-Application
register	O
,	O
ST(x )	O
,	O
in	O
a	O
role	O
similar	O
to	O
a	O
traditional	O
accumulator	B-General_Concept
(	O
a	O
combined	O
destination	O
and	O
left	O
operand	O
)	O
.	O
</s>
<s>
Furthermore	O
,	O
the	O
contents	O
in	O
ST(0 )	O
can	O
be	O
exchanged	O
with	O
another	O
stack	B-Application
register	O
using	O
an	O
instruction	O
called	O
FXCH	O
ST(x )	O
.	O
</s>
<s>
These	O
properties	O
make	O
the	O
x87	B-Application
stack	B-Application
usable	O
as	O
seven	O
freely	O
addressable	O
registers	O
plus	O
a	O
dedicated	O
accumulator	B-General_Concept
(	O
or	O
as	O
seven	O
independent	O
accumulators	B-General_Concept
)	O
.	O
</s>
<s>
This	O
is	O
especially	O
applicable	O
on	O
superscalar	B-General_Concept
x86	B-Operating_System
processors	O
(	O
such	O
as	O
the	O
Pentium	B-General_Concept
of	O
1993	O
and	O
later	O
)	O
,	O
where	O
these	O
exchange	O
instructions	O
(	O
codes	O
D9C8	O
..	O
D9CFh	O
)	O
are	O
optimized	O
down	O
to	O
a	O
zero	O
clock	O
penalty	O
by	O
using	O
one	O
of	O
the	O
integer	O
paths	O
for	O
FXCH	O
ST(x )	O
in	O
parallel	O
with	O
the	O
FPU	O
instruction	O
.	O
</s>
<s>
Despite	O
being	O
natural	O
and	O
convenient	O
for	O
human	O
assembly	B-Language
language	I-Language
programmers	O
,	O
some	O
compiler	B-Language
writers	O
have	O
found	O
it	O
complicated	O
to	O
construct	O
automatic	O
code	B-Application
generators	I-Application
that	O
schedule	O
x87	B-Application
code	O
effectively	O
.	O
</s>
<s>
Such	O
a	O
stack-based	O
interface	O
potentially	O
can	O
minimize	O
the	O
need	O
to	O
save	O
scratch	O
variables	O
in	O
function	O
calls	O
compared	O
with	O
a	O
register-based	O
interface	O
(	O
although	O
,	O
historically	O
,	O
design	O
issues	O
in	O
the	O
8087	O
implementation	O
limited	O
that	O
potential	O
.	O
)	O
</s>
<s>
The	O
x87	B-Application
provides	O
single-precision	O
,	O
double-precision	O
and	O
80-bit	O
double-extended	B-Algorithm
precision	I-Algorithm
binary	B-Algorithm
floating-point	I-Algorithm
arithmetic	I-Algorithm
as	O
per	O
the	O
IEEE	O
754-1985	O
standard	O
.	O
</s>
<s>
By	O
default	O
,	O
the	O
x87	B-Application
processors	O
all	O
use	O
80-bit	O
double-extended	B-Algorithm
precision	I-Algorithm
internally	O
(	O
to	O
allow	O
sustained	O
precision	B-Architecture
over	O
many	O
calculations	O
,	O
see	O
IEEE	O
754	O
design	O
rationale	O
)	O
.	O
</s>
<s>
A	O
given	O
sequence	O
of	O
arithmetic	O
operations	O
may	O
thus	O
behave	O
slightly	O
differently	O
compared	O
to	O
a	O
strict	O
single-precision	O
or	O
double-precision	O
IEEE	O
754	O
FPU	O
.	O
</s>
<s>
As	O
this	O
may	O
sometimes	O
be	O
problematic	O
for	O
some	O
semi-numerical	O
calculations	O
written	O
to	O
assume	O
double	O
precision	B-Architecture
for	O
correct	O
operation	O
,	O
to	O
avoid	O
such	O
problems	O
,	O
the	O
x87	B-Application
can	O
be	O
configured	O
using	O
a	O
special	O
configuration/status	O
register	O
to	O
automatically	O
round	O
to	O
single	O
or	O
double	O
precision	B-Architecture
after	O
each	O
operation	O
.	O
</s>
<s>
Since	O
the	O
introduction	O
of	O
SSE2	B-General_Concept
,	O
the	O
x87	B-Application
instructions	O
are	O
not	O
as	O
essential	O
as	O
they	O
once	O
were	O
,	O
but	O
remain	O
important	O
as	O
a	O
high-precision	O
scalar	O
unit	O
for	O
numerical	O
calculations	O
sensitive	O
to	O
round-off	B-Algorithm
error	I-Algorithm
and	O
requiring	O
the	O
64-bit	B-Device
mantissa	B-Algorithm
precision	I-Algorithm
and	O
extended	O
range	O
available	O
in	O
the	O
80-bit	O
format	O
.	O
</s>
<s>
Clock	O
cycle	O
counts	O
for	O
examples	O
of	O
typical	O
x87	B-Application
FPU	I-Application
instructions	O
(	O
only	O
register-register	O
versions	O
shown	O
here	O
)	O
.	O
</s>
<s>
The	O
A	O
...	O
B	O
notation	O
(	O
minimum	O
to	O
maximum	O
)	O
covers	O
timing	O
variations	O
dependent	O
on	O
transient	O
pipeline	O
status	O
and	O
the	O
arithmetic	B-Architecture
precision	I-Architecture
chosen	O
(	O
32	O
,	O
64	O
or	O
80	O
bits	O
)	O
;	O
it	O
also	O
includes	O
variations	O
due	O
to	O
numerical	O
cases	O
(	O
such	O
as	O
the	O
number	O
of	O
set	O
bits	O
,	O
zero	O
,	O
etc	O
.	O
)	O
.	O
</s>
<s>
x87	B-Application
implementation	O
FADD	O
FMUL	O
FDIV	O
FXCH	O
FCOM	O
FSQRT	O
FPTAN	O
FPATAN	O
Max	O
clock(MHz )	O
Peak	O
FMUL( 	O
millions/s	O
)	O
FMUL§rel	O
.	O
</s>
<s>
5	O
MHz	O
8087	O
8087	O
70	O
…	O
100	O
90	O
…	O
145	O
193	O
…	O
203	O
10	O
…	O
15	O
40	O
…	O
50	O
180	O
…	O
186	B-Device
30	O
…	O
540	O
250	O
…	O
800	O
5	O
→	O
10	O
0.034	O
…	O
0.055	O
→	O
0.100	O
…	O
0.111	O
1	O
→	O
2×	O
as	O
fast	O
80287	O
(	O
original	O
)	O
6	O
→	O
12	O
0.041	O
…	O
0.066	O
→	O
0.083	O
…	O
0.133	O
1.2	O
→	O
2.4	O
×	O
80387	O
(	O
and	O
later	O
287	O
models	O
)	O
23	O
…	O
34	O
29	O
…	O
57	O
88	O
…	O
91	O
18	O
24	O
122	O
…	O
129	O
191	O
…	O
497	O
314	O
…	O
487	O
16	O
→	O
33	O
0.280	O
…	O
0.552	O
→	O
0.580	O
…	O
1.1	O
~	O
10	O
→	O
20×	O
80486	B-General_Concept
(	O
or	O
80487	O
)	O
8	O
…	O
20	O
16	O
73	O
4	O
4	O
83	O
…	O
87	O
200	O
…	O
273	O
218	O
…	O
303	O
16	O
→	O
50	O
1.0	O
→	O
3.1	O
~	O
18	O
→	O
56×	O
Cyrix	B-General_Concept
6x86	I-General_Concept
,	O
Cyrix	O
MII	O
4	O
…	O
7	O
4	O
…	O
6	O
24	O
…	O
34	O
2	O
4	O
59	O
…	O
60	O
117	O
…	O
129	O
97	O
…	O
161	O
66	O
→	O
300	O
11	O
…	O
16	O
→	O
50	O
…	O
75	O
~	O
320	O
→	O
1400×	O
AMD	B-Architecture
K6	I-Architecture
(	O
including	O
K6	B-Architecture
II/III	O
)	O
2	O
2	O
21	O
…	O
41	O
2	O
3	O
21	O
…	O
41	O
?	O
</s>
<s>
1	O
…	O
4	O
70	O
17	O
…	O
173	O
19	O
…	O
134	O
60	O
→	O
300	O
20	O
…	O
60	O
→	O
100	O
…	O
300	O
~	O
1100	O
→	O
5400×	O
Pentium	B-Device
Pro	I-Device
1	O
…	O
3	O
2	O
…	O
5	O
16	O
…	O
56	O
1	O
28	O
…	O
68	O
?	O
</s>
<s>
150	O
→	O
200	O
30	O
…	O
75	O
→	O
40	O
…	O
100	O
~	O
1400	O
→	O
1800×	O
Pentium	B-General_Concept
II	I-General_Concept
/	O
III	O
1	O
…	O
3	O
2	O
…	O
5	O
17	O
…	O
38	O
1	O
27	O
…	O
50	O
?	O
</s>
<s>
233	O
→	O
1400	O
47	O
…	O
116	O
→	O
280	O
…	O
700	O
~	O
2100	O
→	O
13000×	O
Athlon	B-Architecture
(	O
K7	B-Architecture
)	O
1	O
…	O
4	O
1	O
…	O
4	O
13	O
…	O
24	O
1	O
…	O
2	O
16	O
…	O
35	O
?	O
</s>
<s>
500	O
→	O
2330	O
125	O
…	O
500	O
→	O
580	O
…	O
2330	O
~	O
9000	O
→	O
42000×	O
Athlon	B-Architecture
64	O
(	O
K8	O
)	O
1000	O
→	O
3200	O
250	O
…	O
1000	O
→	O
800	O
…	O
3200	O
~	O
18000	O
→	O
58000×	O
Pentium	B-General_Concept
4	I-General_Concept
1	O
…	O
5	O
2	O
…	O
7	O
20	O
…	O
43	O
multiplecycles	O
1	O
20	O
…	O
43	O
?	O
</s>
<s>
*	O
An	O
effective	O
zero	O
clock	O
delay	O
is	O
often	O
possible	O
,	O
via	O
superscalar	B-General_Concept
execution	I-General_Concept
.	O
</s>
<s>
§	O
The	O
5	O
MHz	O
8087	O
was	O
the	O
original	O
x87	B-Application
processor	O
.	O
</s>
<s>
Compared	O
to	O
typical	O
software-implemented	O
floating-point	B-Algorithm
routines	O
on	O
an	O
8086	B-General_Concept
(	O
without	O
an	O
8087	O
)	O
,	O
the	O
factors	O
would	O
be	O
even	O
larger	O
,	O
perhaps	O
by	O
another	O
factor	O
of	O
10	O
(	O
i.e.	O
,	O
a	O
correct	O
floating-point	B-Algorithm
addition	O
in	O
assembly	B-Language
language	I-Language
may	O
well	O
consume	O
over	O
1000	O
cycles	O
)	O
.	O
</s>
<s>
Companies	O
that	O
have	O
designed	O
or	O
manufactured	O
floating-point	B-General_Concept
units	I-General_Concept
compatible	O
with	O
the	O
Intel	O
8087	O
or	O
later	O
models	O
include	O
AMD	O
(	O
287	O
,	O
387	O
,	O
486DX	B-General_Concept
,	O
5x86	O
,	O
K5	O
,	O
K6	B-Architecture
,	O
K7	B-Architecture
,	O
K8	O
)	O
,	O
Chips	O
and	O
Technologies	O
(	O
the	O
Super	O
MATH	B-General_Concept
coprocessors	I-General_Concept
)	O
,	O
Cyrix	O
(	O
the	O
FasMath	O
,	O
Cx87SLC	O
,	O
Cx87DLC	O
,	O
etc.	O
,	O
6x86	B-General_Concept
,	O
Cyrix	O
MII	O
)	O
,	O
Fujitsu	O
(	O
early	O
Pentium	B-General_Concept
Mobile	O
etc	O
.	O
</s>
<s>
)	O
,	O
Harris	O
Semiconductor	O
(	O
manufactured	O
80387	O
and	O
486DX	B-General_Concept
processors	O
)	O
,	O
IBM	O
(	O
various	O
387	O
and	O
486	B-General_Concept
designs	O
)	O
,	O
IDT	O
(	O
the	O
WinChip	B-Device
,	O
C3	O
,	O
C7	O
,	O
Nano	O
,	O
etc	O
.	O
</s>
<s>
)	O
,	O
LC	O
Technology	O
(	O
the	O
Green	O
MATH	B-General_Concept
coprocessors	I-General_Concept
)	O
,	O
National	O
Semiconductor	O
(	O
the	O
Geode	O
GX1	O
,	O
Geode	O
GXm	O
,	O
etc	O
.	O
</s>
<s>
)	O
,	O
NexGen	O
(	O
the	O
Nx587	O
)	O
,	O
Rise	O
Technology	O
(	O
the	O
mP6	O
)	O
,	O
ST	O
Microelectronics	O
(	O
manufactured	O
486DX	B-General_Concept
,	O
5x86	O
,	O
etc	O
.	O
</s>
<s>
)	O
,	O
Texas	O
Instruments	O
(	O
manufactured	O
486DX	B-General_Concept
processors	O
etc	O
.	O
</s>
<s>
)	O
,	O
Transmeta	O
(	O
the	O
TM5600	O
and	O
TM5800	O
)	O
,	O
ULSI	O
(	O
the	O
Math·Co	O
coprocessors	B-General_Concept
)	O
,	O
VIA	O
(	O
the	O
C3	O
,	O
C7	O
,	O
and	O
Nano	O
,	O
etc	O
.	O
</s>
<s>
)	O
,	O
and	O
Xtend	O
(	O
the	O
83S87SX-25	O
and	O
other	O
coprocessors	B-General_Concept
)	O
.	O
</s>
<s>
The	O
8087	O
was	O
the	O
first	O
math	B-General_Concept
coprocessor	I-General_Concept
for	O
16-bit	O
processors	O
designed	O
by	O
Intel	O
.	O
</s>
<s>
It	O
was	O
built	O
to	O
be	O
paired	O
with	O
the	O
Intel	B-Device
8088	I-Device
or	O
8086	B-General_Concept
microprocessors	I-General_Concept
.	O
</s>
<s>
(	O
Intel	O
's	O
earlier	O
8231	B-General_Concept
and	I-General_Concept
8232	I-General_Concept
floating-point	B-General_Concept
processors	I-General_Concept
,	O
marketed	O
for	O
use	O
with	O
the	O
i8080	O
CPU	O
,	O
were	O
in	O
fact	O
licensed	O
versions	O
of	O
AMD	O
's	O
Am9511	O
and	O
Am9512	O
FPUs	O
from	O
1977	O
and	O
1979	O
.	O
)	O
</s>
<s>
The	O
80187	O
(	O
80C187	O
)	O
is	O
the	O
math	B-General_Concept
coprocessor	I-General_Concept
for	O
the	O
Intel	B-Device
80186	I-Device
CPU	O
.	O
</s>
<s>
It	O
is	O
incapable	O
of	O
operating	O
with	O
the	O
80188	O
,	O
as	O
the	O
80188	O
has	O
an	O
eight-bit	O
data	B-General_Concept
bus	I-General_Concept
;	O
the	O
80188	O
can	O
only	O
use	O
the	O
8087	O
.	O
</s>
<s>
The	O
80187	O
did	O
not	O
appear	O
at	O
the	O
same	O
time	O
as	O
the	O
80186	B-Device
and	O
80188	O
,	O
but	O
was	O
in	O
fact	O
launched	O
after	O
the	O
80287	O
and	O
the	O
80387	O
.	O
</s>
<s>
The	O
80287	O
(	O
i287	O
)	O
is	O
the	O
math	B-General_Concept
coprocessor	I-General_Concept
for	O
the	O
Intel	B-General_Concept
80286	I-General_Concept
series	O
of	O
microprocessors	B-Architecture
.	O
</s>
<s>
The	O
available	O
10MHz	O
Intel	O
80287-10	O
Numerics	B-Algorithm
Coprocessor	B-General_Concept
version	O
was	O
for	O
250USD	O
in	O
quantities	O
of	O
100	O
.	O
</s>
<s>
The	O
80287XL	O
is	O
actually	O
an	O
80387SX	B-Device
with	O
a	O
287	O
pinout	O
.	O
</s>
<s>
It	O
contains	O
an	O
internal	O
3/2	O
multiplier	O
,	O
so	O
that	O
motherboards	O
that	O
ran	O
the	O
coprocessor	B-General_Concept
at	O
2/3	O
CPU	O
speed	O
could	O
instead	O
run	O
the	O
FPU	O
at	O
the	O
same	O
speed	O
of	O
the	O
CPU	O
.	O
</s>
<s>
Other	O
287	O
models	O
with	O
387-like	O
performance	O
are	O
the	O
Intel	O
80C287	O
,	O
built	O
using	O
CHMOS	O
III	O
,	O
and	O
the	O
AMD	O
80EC287	O
manufactured	O
in	O
AMD	O
's	O
CMOS	B-Device
process	O
,	O
using	O
only	O
fully	O
static	O
gates	O
.	O
</s>
<s>
The	O
80287	O
and	O
80287XL	O
work	O
with	O
the	O
80386	B-General_Concept
microprocessor	B-Architecture
and	O
were	O
initially	O
the	O
only	O
coprocessors	B-General_Concept
available	O
for	O
the	O
80386	B-General_Concept
until	O
the	O
introduction	O
of	O
the	O
80387	O
in	O
1987	O
.	O
</s>
<s>
Finally	O
,	O
they	O
were	O
able	O
to	O
work	O
with	O
the	O
Cyrix	B-Device
Cx486SLC	I-Device
.	O
</s>
<s>
However	O
,	O
for	O
both	O
of	O
these	O
chips	O
the	O
80387	O
is	O
strongly	O
preferred	O
for	O
its	O
higher	O
performance	O
and	O
the	O
greater	O
capability	O
of	O
its	O
instruction	B-General_Concept
set	I-General_Concept
.	O
</s>
<s>
The	O
80387	O
(	O
387	O
or	O
i387	O
)	O
is	O
the	O
first	O
Intel	O
coprocessor	B-General_Concept
to	O
be	O
fully	O
compliant	O
with	O
the	O
IEEE	O
754-1985	O
standard	O
.	O
</s>
<s>
Released	O
in	O
1987	O
,	O
two	O
years	O
after	O
the	O
386	B-General_Concept
chip	O
,	O
the	O
i387	O
includes	O
much	O
improved	O
speed	O
over	O
Intel	O
's	O
previous	O
8087/80287	O
coprocessors	B-General_Concept
and	O
improved	O
characteristics	O
of	O
its	O
trigonometric	O
functions	O
.	O
</s>
<s>
Without	O
a	O
coprocessor	B-General_Concept
,	O
the	O
386	B-General_Concept
normally	O
performs	O
floating-point	B-Algorithm
arithmetic	I-Algorithm
through	O
(	O
relatively	O
slow	O
)	O
software	O
routines	O
,	O
implemented	O
at	O
runtime	O
through	O
a	O
software	O
exception	B-General_Concept
handler	I-General_Concept
.	O
</s>
<s>
When	O
a	O
math	B-General_Concept
coprocessor	I-General_Concept
is	O
paired	O
with	O
the	O
386	B-General_Concept
,	O
the	O
coprocessor	B-General_Concept
performs	O
the	O
floating-point	B-Algorithm
arithmetic	I-Algorithm
in	O
hardware	O
,	O
returning	O
results	O
much	O
faster	O
than	O
an	O
(	O
emulating	O
)	O
software	O
library	O
call	O
.	O
</s>
<s>
The	O
i387	O
is	O
compatible	O
only	O
with	O
the	O
standard	O
i386	B-General_Concept
chip	O
,	O
which	O
has	O
a	O
32-bit	O
processor	O
bus	O
.	O
</s>
<s>
The	O
later	O
cost-reduced	O
i386SX	O
,	O
which	O
has	O
a	O
narrower	O
16-bit	O
data	B-General_Concept
bus	I-General_Concept
,	O
can	O
not	O
interface	O
with	O
the	O
i387	O
's	O
32-bit	O
bus	O
.	O
</s>
<s>
The	O
i386SX	O
requires	O
its	O
own	O
coprocessor	B-General_Concept
,	O
the	O
80387SX	B-Device
,	O
which	O
is	O
compatible	O
with	O
the	O
SX	O
's	O
narrower	O
16-bit	O
data	B-General_Concept
bus	I-General_Concept
.	O
</s>
<s>
The	O
i487SX	O
(	O
P23N	O
)	O
was	O
marketed	O
as	O
a	O
floating-point	B-General_Concept
unit	I-General_Concept
coprocessor	B-General_Concept
for	O
Intel	O
i486SX	B-Device
machines	O
.	O
</s>
<s>
It	O
actually	O
contained	O
a	O
full-blown	O
i486DX	B-General_Concept
implementation	O
.	O
</s>
<s>
When	O
installed	O
into	O
an	O
i486SX	B-Device
system	O
,	O
the	O
i487	O
disabled	O
the	O
main	O
CPU	O
and	O
took	O
over	O
all	O
CPU	O
operations	O
.	O
</s>
<s>
The	O
i487	O
took	O
measures	O
to	O
detect	O
the	O
presence	O
of	O
an	O
i486SX	B-Device
and	O
would	O
not	O
function	O
without	O
the	O
original	O
CPU	O
in	O
place	O
.	O
</s>
<s>
The	O
Nx587	O
was	O
the	O
last	O
FPU	O
for	O
x86	B-Operating_System
to	O
be	O
manufactured	O
separately	O
from	O
the	O
CPU	O
,	O
in	O
this	O
case	O
NexGen	O
's	O
Nx586	B-Device
.	O
</s>
