<s>
The	O
8086	B-General_Concept
(	O
also	O
called	O
iAPX	B-General_Concept
86	I-General_Concept
)	O
is	O
a	B-Application
16-bit	B-Device
microprocessor	B-Architecture
chip	O
designed	O
by	O
Intel	O
between	O
early	O
1976	O
and	O
June	O
8	O
,	O
1978	O
,	O
when	O
it	O
was	O
released	O
.	O
</s>
<s>
The	O
Intel	B-Device
8088	I-Device
,	O
released	O
July	O
1	O
,	O
1979	O
,	O
is	O
a	B-Application
slightly	O
modified	O
chip	O
with	O
an	O
external	O
8-bit	O
data	B-General_Concept
bus	I-General_Concept
(	O
allowing	O
the	O
use	O
of	O
cheaper	O
and	O
fewer	O
supporting	O
ICs	O
)	O
,	O
and	O
is	O
notable	O
as	O
the	O
processor	O
used	O
in	O
the	O
original	O
IBM	B-Device
PC	I-Device
design	O
.	O
</s>
<s>
The	O
8086	B-General_Concept
gave	O
rise	O
to	O
the	O
x86	B-Operating_System
architecture	I-Operating_System
,	O
which	O
eventually	O
became	O
Intel	O
's	O
most	O
successful	O
line	O
of	O
processors	O
.	O
</s>
<s>
On	O
June	O
5	O
,	O
2018	O
,	O
Intel	O
released	O
a	B-Application
limited-edition	O
CPU	B-General_Concept
celebrating	O
the	O
40th	O
anniversary	O
of	O
the	O
Intel	B-General_Concept
8086	I-General_Concept
,	O
called	O
the	O
Intel	B-Device
Core	I-Device
i7-8086K	I-Device
.	O
</s>
<s>
In	O
1972	O
,	O
Intel	O
launched	O
the	O
8008	B-General_Concept
,	O
Intel	O
's	O
first	O
8-bit	O
microprocessor	B-Architecture
.	O
</s>
<s>
It	O
implemented	O
an	O
instruction	B-General_Concept
set	I-General_Concept
designed	O
by	O
Datapoint	O
Corporation	O
with	O
programmable	O
CRT	B-General_Concept
terminals	I-General_Concept
in	O
mind	O
,	O
which	O
also	O
proved	O
to	O
be	O
fairly	O
general-purpose	O
.	O
</s>
<s>
The	O
device	O
needed	O
several	O
additional	O
ICs	O
to	O
produce	O
a	B-Application
functional	O
computer	O
,	O
in	O
part	O
due	O
to	O
it	O
being	O
packaged	O
in	O
a	B-Application
small	O
18-pin	O
"	O
memory	O
package	O
"	O
,	O
which	O
ruled	O
out	O
the	O
use	O
of	O
a	B-Application
separate	O
address	O
bus	O
(	O
Intel	O
was	O
primarily	O
a	B-Application
DRAM	O
manufacturer	O
at	O
the	O
time	O
)	O
.	O
</s>
<s>
Two	O
years	O
later	O
,	O
Intel	O
launched	O
the	O
8080	B-General_Concept
,	O
employing	O
the	O
new	O
40-pin	O
DIL	B-Algorithm
packages	I-Algorithm
originally	O
developed	O
for	O
calculator	B-Application
ICs	O
to	O
enable	O
a	B-Application
separate	O
address	O
bus	O
.	O
</s>
<s>
It	O
has	O
an	O
extended	O
instruction	B-General_Concept
set	I-General_Concept
that	O
is	O
source-compatible	B-General_Concept
(	O
not	O
binary	B-General_Concept
compatible	I-General_Concept
)	O
with	O
the	O
8008	B-General_Concept
and	O
also	O
includes	O
some	O
16-bit	B-Device
instructions	O
to	O
make	O
programming	O
easier	O
.	O
</s>
<s>
The	O
8080	B-General_Concept
device	O
was	O
eventually	O
replaced	O
by	O
the	O
depletion-load-based	O
8085	B-General_Concept
(	O
1977	O
)	O
,	O
which	O
sufficed	O
with	O
a	B-Application
single	O
+5V	O
power	O
supply	O
instead	O
of	O
the	O
three	O
different	O
operating	O
voltages	O
of	O
earlier	O
chips	O
.	O
</s>
<s>
Other	O
well	O
known	O
8-bit	O
microprocessors	B-Architecture
that	O
emerged	O
during	O
these	O
years	O
are	O
Motorola	B-Device
6800	I-Device
(	O
1974	O
)	O
,	O
General	B-Architecture
Instrument	I-Architecture
PIC16X	I-Architecture
(	O
1975	O
)	O
,	O
MOS	B-General_Concept
Technology	I-General_Concept
6502	I-General_Concept
(	O
1975	O
)	O
,	O
Zilog	B-General_Concept
Z80	I-General_Concept
(	O
1976	O
)	O
,	O
and	O
Motorola	B-Device
6809	I-Device
(	O
1978	O
)	O
.	O
</s>
<s>
The	O
8086	B-General_Concept
project	O
started	O
in	O
May	O
1976	O
and	O
was	O
originally	O
intended	O
as	O
a	B-Application
temporary	O
substitute	O
for	O
the	O
ambitious	O
and	O
delayed	O
iAPX	B-Device
432	I-Device
project	O
.	O
</s>
<s>
It	O
was	O
an	O
attempt	O
to	O
draw	O
attention	O
from	O
the	O
less-delayed	O
16-bit	B-Device
and	O
32-bit	O
processors	O
of	O
other	O
manufacturers	O
—	O
Motorola	O
,	O
Zilog	O
,	O
and	O
National	O
Semiconductor	O
.	O
</s>
<s>
Whereas	O
the	O
8086	B-General_Concept
was	O
a	B-Application
16-bit	B-Device
microprocessor	B-Architecture
,	O
it	O
used	O
the	O
same	O
microarchitecture	B-General_Concept
as	O
Intel	O
's	O
8-bit	O
microprocessors	B-Architecture
(	O
8008	B-General_Concept
,	O
8080	B-General_Concept
,	O
and	O
8085	B-General_Concept
)	O
.	O
</s>
<s>
This	O
allowed	O
assembly	B-Language
language	I-Language
programs	O
written	O
in	O
8-bit	O
to	O
seamlessly	O
migrate	O
.	O
</s>
<s>
Instructions	O
were	O
added	O
to	O
assist	O
source	O
code	O
compilation	O
of	O
nested	O
functions	O
in	O
the	O
ALGOL-family	O
of	O
languages	O
,	O
including	O
Pascal	B-Application
and	O
PL/M	B-Language
.	O
</s>
<s>
According	O
to	O
principal	O
architect	O
Stephen	O
P	B-General_Concept
.	O
Morse	O
,	O
this	O
was	O
a	B-Application
result	O
of	O
a	B-Application
more	O
software-centric	O
approach	O
.	O
</s>
<s>
Other	O
enhancements	O
included	O
microcode	B-Device
instructions	O
for	O
the	O
multiply	O
and	O
divide	O
assembly	B-Language
language	I-Language
instructions	O
.	O
</s>
<s>
Designers	O
also	O
anticipated	O
coprocessors	B-General_Concept
,	O
such	O
as	O
8087	B-Device
and	O
8089	B-Device
,	O
so	O
the	O
bus	O
structure	O
was	O
designed	O
to	O
be	O
flexible	O
.	O
</s>
<s>
The	O
first	O
revision	O
of	O
the	O
instruction	B-General_Concept
set	I-General_Concept
and	O
high	O
level	O
architecture	O
was	O
ready	O
after	O
about	O
three	O
months	O
,	O
and	O
as	O
almost	O
no	O
CAD	O
tools	O
were	O
used	O
,	O
four	O
engineers	O
and	O
12layout	O
people	O
were	O
simultaneously	O
working	O
on	O
the	O
chip	O
.	O
</s>
<s>
The	O
8086	B-General_Concept
took	O
a	B-Application
little	O
more	O
than	O
two	O
years	O
from	O
idea	O
to	O
working	O
product	O
,	O
which	O
was	O
considered	O
rather	O
fast	O
for	O
a	B-Application
complex	O
design	O
in	O
1976	O
–	O
1978	O
.	O
</s>
<s>
The	O
8086	B-General_Concept
was	O
sequenced	O
using	O
a	B-Application
mixture	O
of	O
random	B-General_Concept
logic	I-General_Concept
and	O
microcode	B-Device
and	O
was	O
implemented	O
using	O
depletion-load	B-Algorithm
nMOS	I-Algorithm
circuitry	O
with	O
approximately	O
20,000	O
active	O
transistors	B-Application
(	O
29,000	O
counting	O
all	O
ROM	B-Device
and	O
PLA	O
sites	O
)	O
.	O
</s>
<s>
It	O
was	O
soon	O
moved	O
to	O
a	B-Application
new	O
refined	O
nMOS	O
manufacturing	O
process	O
called	O
HMOS	O
(	O
for	O
High	O
performance	O
MOS	O
)	O
that	O
Intel	O
originally	O
developed	O
for	O
manufacturing	O
of	O
fast	O
static	B-Architecture
RAM	I-Architecture
products	O
.	O
</s>
<s>
This	O
was	O
followed	O
by	O
HMOS-II	O
,	O
HMOS-III	O
versions	O
,	O
and	O
,	O
eventually	O
,	O
a	B-Application
fully	O
static	O
CMOS	B-Device
version	O
for	O
battery	O
powered	O
devices	O
,	O
manufactured	O
using	O
Intel	O
's	O
CHMOS	O
processes	O
.	O
</s>
<s>
The	O
architecture	O
was	O
defined	O
by	O
Stephen	O
P	B-General_Concept
.	O
Morse	O
with	O
some	O
help	O
from	O
Bruce	O
Ravenel	O
(	O
the	O
architect	O
of	O
the	O
8087	B-Device
)	O
in	O
refining	O
the	O
final	O
revisions	O
.	O
</s>
<s>
Logic	O
designer	O
Jim	O
McKevitt	O
and	O
John	O
Bayliss	O
were	O
the	O
lead	O
engineers	O
of	O
the	O
hardware-level	O
development	O
team	O
and	O
Bill	O
Pohlman	O
the	O
manager	O
for	O
the	O
project	O
.	O
</s>
<s>
The	O
legacy	O
of	O
the	O
8086	B-General_Concept
is	O
enduring	O
in	O
the	O
basic	O
instruction	B-General_Concept
set	I-General_Concept
of	O
today	O
's	O
personal	O
computers	O
and	O
servers	O
;	O
the	O
8086	B-General_Concept
also	O
lent	O
its	O
last	O
two	O
digits	O
to	O
later	O
extended	O
versions	O
of	O
the	O
design	O
,	O
such	O
as	O
the	O
Intel	B-General_Concept
286	I-General_Concept
and	O
the	O
Intel	B-General_Concept
386	I-General_Concept
,	O
all	O
of	O
which	O
eventually	O
became	O
known	O
as	O
the	O
x86	B-Operating_System
family	O
.	O
</s>
<s>
(	O
Another	O
reference	O
is	O
that	O
the	O
PCI	B-Architecture
Vendor	I-Architecture
ID	I-Architecture
for	O
Intel	O
devices	O
is	O
8086h	O
.	O
)	O
</s>
<s>
All	O
internal	O
registers	B-General_Concept
,	O
as	O
well	O
as	O
internal	O
and	O
external	O
data	B-General_Concept
buses	I-General_Concept
,	O
are	O
16bits	O
wide	O
,	O
which	O
firmly	O
established	O
the	O
"	O
16-bit	B-Device
microprocessor	B-Architecture
"	O
identity	O
of	O
the	O
8086	B-General_Concept
.	O
</s>
<s>
A	B-Application
20-bit	O
external	O
address	O
bus	O
provides	O
a	B-Application
1MiB	O
physical	O
address	O
space	O
(	O
220	O
=	O
1,048,576	O
x	O
1	O
byte	B-Application
)	O
.	O
</s>
<s>
The	O
data	B-General_Concept
bus	I-General_Concept
is	O
multiplexed	B-Architecture
with	O
the	O
address	O
bus	O
in	O
order	O
to	O
fit	O
all	O
of	O
the	O
control	O
lines	O
into	O
a	B-Application
standard	O
40-pin	O
dual	B-Algorithm
in-line	I-Algorithm
package	I-Algorithm
.	O
</s>
<s>
It	O
provides	O
a	B-Application
16-bit	B-Device
I/O	B-Architecture
address	I-Architecture
bus	O
,	O
supporting	O
64KB	O
of	O
separate	O
I/O	O
space	O
.	O
</s>
<s>
Programming	O
over	O
64KB	O
memory	O
boundaries	O
involves	O
adjusting	O
the	O
segment	B-Device
registers	I-Device
(	O
see	O
below	O
)	O
;	O
this	O
difficulty	O
existed	O
until	O
the	O
80386	B-General_Concept
architecture	O
introduced	O
wider	O
(	O
32-bit	O
)	O
registers	B-General_Concept
(	O
the	O
memory	O
management	O
hardware	B-Architecture
in	O
the	O
80286	B-General_Concept
did	O
not	O
help	O
in	O
this	O
regard	O
,	O
as	O
its	O
registers	B-General_Concept
are	O
still	O
only	O
16	B-Device
bits	I-Device
wide	O
)	O
.	O
</s>
<s>
The	O
former	O
mode	O
is	O
intended	O
for	O
small	O
single-processor	O
systems	O
,	O
while	O
the	O
latter	O
is	O
for	O
medium	O
or	O
large	O
systems	O
using	O
more	O
than	O
one	O
processor	O
(	O
a	B-Application
kind	O
of	O
multiprocessor	O
mode	O
)	O
.	O
</s>
<s>
Maximum	O
mode	O
is	O
required	O
when	O
using	O
an	O
8087	B-Device
or	O
8089	B-Device
coprocessor	B-General_Concept
.	O
</s>
<s>
Changing	O
the	O
state	O
of	O
pin	O
33	O
changes	O
the	O
function	O
of	O
certain	O
other	O
pins	O
,	O
most	O
of	O
which	O
have	O
to	O
do	O
with	O
how	O
the	O
CPU	B-General_Concept
handles	O
the	O
(	O
local	O
)	O
bus	O
.	O
</s>
<s>
In	O
minimum	O
mode	O
,	O
all	O
control	O
signals	O
are	O
generated	O
by	O
the	O
8086	B-General_Concept
itself	O
.	O
</s>
<s>
The	O
8086	B-General_Concept
has	O
eight	O
more	O
or	O
less	O
general	O
16-bit	B-Device
registers	B-General_Concept
(	O
including	O
the	O
stack	B-General_Concept
pointer	I-General_Concept
but	O
excluding	O
the	O
instruction	B-General_Concept
pointer	I-General_Concept
,	O
flag	B-General_Concept
register	I-General_Concept
and	O
segment	B-Device
registers	I-Device
)	O
.	O
</s>
<s>
Four	O
of	O
them	O
,	O
AX	B-General_Concept
,	O
BX	O
,	O
CX	O
,	O
DX	O
,	O
can	O
also	O
be	O
accessed	O
as	O
twice	O
as	O
many	O
8-bit	O
registers	B-General_Concept
(	O
see	O
figure	O
)	O
while	O
the	O
other	O
four	O
,	O
SI	B-General_Concept
,	O
DI	O
,	O
BP	O
,	O
SP	B-General_Concept
,	O
are	O
16-bit	B-Device
only	O
.	O
</s>
<s>
Due	O
to	O
a	B-Application
compact	O
encoding	O
inspired	O
by	O
8-bit	O
processors	O
,	O
most	O
instructions	O
are	O
one-address	O
or	O
two-address	O
operations	O
,	O
which	O
means	O
that	O
the	O
result	O
is	O
stored	O
in	O
one	O
of	O
the	O
operands	O
.	O
</s>
<s>
At	O
most	O
one	O
of	O
the	O
operands	O
can	O
be	O
in	O
memory	O
,	O
but	O
this	O
memory	O
operand	O
can	O
also	O
be	O
the	O
destination	O
,	O
while	O
the	O
other	O
operand	O
,	O
the	O
source	O
,	O
can	O
be	O
either	O
register	B-General_Concept
or	O
immediate	O
.	O
</s>
<s>
A	B-Application
single	O
memory	O
location	O
can	O
also	O
often	O
be	O
used	O
as	O
both	O
source	O
and	O
destination	O
which	O
,	O
among	O
other	O
factors	O
,	O
further	O
contributes	O
to	O
a	B-Application
code	O
density	O
comparable	O
to	O
(	O
and	O
often	O
better	O
than	O
)	O
most	O
eight-bit	O
machines	O
at	O
the	O
time	O
.	O
</s>
<s>
The	O
degree	O
of	O
generality	O
of	O
most	O
registers	B-General_Concept
is	O
much	O
greater	O
than	O
in	O
the	O
8080	B-General_Concept
or	O
8085	B-General_Concept
.	O
</s>
<s>
However	O
,	O
8086	B-General_Concept
registers	B-General_Concept
were	O
more	O
specialized	O
than	O
in	O
most	O
contemporary	O
minicomputers	B-Architecture
and	O
are	O
also	O
used	O
implicitly	O
by	O
some	O
instructions	O
.	O
</s>
<s>
While	O
perfectly	O
sensible	O
for	O
the	O
assembly	O
programmer	O
,	O
this	O
makes	O
register	B-General_Concept
allocation	O
for	O
compilers	O
more	O
complicated	O
compared	O
to	O
more	O
orthogonal	O
16-bit	B-Device
and	O
32-bit	O
processors	O
of	O
the	O
time	O
such	O
as	O
the	O
PDP-11	B-Device
,	O
VAX	B-Device
,	O
68000	B-Device
,	O
32016	B-Device
,	O
etc	O
.	O
</s>
<s>
On	O
the	O
other	O
hand	O
,	O
being	O
more	O
regular	O
than	O
the	O
rather	O
minimalistic	O
but	O
ubiquitous	O
8-bit	O
microprocessors	B-Architecture
such	O
as	O
the	O
6502	B-General_Concept
,	O
6800	B-Device
,	O
6809	B-Device
,	O
8085	B-General_Concept
,	O
MCS-48	B-Device
,	O
8051	B-Architecture
,	O
and	O
other	O
contemporary	O
accumulator-based	O
machines	O
,	O
it	O
is	O
significantly	O
easier	O
to	O
construct	O
an	O
efficient	O
code	B-Application
generator	I-Application
for	O
the	O
8086	B-General_Concept
architecture	O
.	O
</s>
<s>
Another	O
factor	O
for	O
this	O
is	O
that	O
the	O
8086	B-General_Concept
also	O
introduced	O
some	O
new	O
instructions	O
(	O
not	O
present	O
in	O
the	O
8080	B-General_Concept
and	O
8085	B-General_Concept
)	O
to	O
better	O
support	O
stack-based	O
high-level	O
programming	O
languages	O
such	O
as	O
Pascal	B-Application
and	O
PL/M	B-Language
;	O
some	O
of	O
the	O
more	O
useful	O
instructions	O
are	O
push	O
mem-op	O
,	O
and	O
ret	O
size	O
,	O
supporting	O
the	O
"	O
Pascal	B-Application
calling	O
convention	O
"	O
directly	O
.	O
</s>
<s>
(	O
Several	O
others	O
,	O
such	O
as	O
push	O
immed	O
and	O
enter	O
,	O
were	O
added	O
in	O
the	O
subsequent	O
80186	B-Device
,	O
80286	B-General_Concept
,	O
and	O
80386	B-General_Concept
processors	O
.	O
)	O
</s>
<s>
A	B-Application
64KB	O
(	O
one	O
segment	B-Device
)	O
stack	B-Application
growing	O
towards	O
lower	O
addresses	O
is	O
supported	O
in	O
hardware	B-Architecture
;	O
16-bit	B-Device
words	O
are	O
pushed	O
onto	O
the	O
stack	B-Application
,	O
and	O
the	O
top	O
of	O
the	O
stack	B-Application
is	O
pointed	O
to	O
by	O
SS	O
:	O
SP	B-General_Concept
.	O
</s>
<s>
There	O
are	O
256interrupts	O
,	O
which	O
can	O
be	O
invoked	O
by	O
both	O
hardware	B-Architecture
and	O
software	O
.	O
</s>
<s>
The	O
interrupts	B-Application
can	O
cascade	O
,	O
using	O
the	O
stack	B-Application
to	O
store	O
the	O
return	O
addresses	O
.	O
</s>
<s>
The	O
8086	B-General_Concept
has	O
64K	O
of	O
8-bit	O
(	O
or	O
alternatively	O
32K	O
of	O
16-bit	B-Device
word	O
)	O
I/O	B-Architecture
port	I-Architecture
space	O
.	O
</s>
<s>
The	O
8086	B-General_Concept
has	O
a	B-Application
16-bit	B-Device
flags	B-General_Concept
register	I-General_Concept
.	O
</s>
<s>
Nine	O
of	O
these	O
condition	O
code	O
flags	O
are	O
active	O
,	O
and	O
indicate	O
the	O
current	O
state	O
of	O
the	O
processor	O
:	O
Carry	B-Algorithm
flag	I-Algorithm
(	O
CF	O
)	O
,	O
Parity	B-General_Concept
flag	I-General_Concept
(	O
PF	O
)	O
,	O
Auxiliary	B-Application
carry	I-Application
flag	I-Application
(	O
AF	O
)	O
,	O
Zero	B-Algorithm
flag	I-Algorithm
(	O
ZF	O
)	O
,	O
Sign	B-Algorithm
flag	I-Algorithm
(	O
SF	O
)	O
,	O
Trap	B-General_Concept
flag	I-General_Concept
(	O
TF	O
)	O
,	O
Interrupt	B-Device
flag	I-Device
(	O
IF	O
)	O
,	O
Direction	B-Device
flag	I-Device
(	O
DF	O
)	O
,	O
and	O
Overflow	B-Algorithm
flag	I-Algorithm
(	O
OF	O
)	O
.	O
</s>
<s>
Also	O
referred	O
to	O
as	O
the	O
status	O
word	O
,	O
the	O
layout	O
of	O
the	O
flags	B-General_Concept
register	I-General_Concept
is	O
as	O
follows	O
:	O
</s>
<s>
There	O
are	O
also	O
four	O
16-bit	B-Device
segment	B-Device
registers	I-Device
(	O
see	O
figure	O
)	O
that	O
allow	O
the	O
8086	B-General_Concept
CPU	B-General_Concept
to	O
access	O
one	O
megabyte	O
of	O
memory	O
in	O
an	O
unusual	O
way	O
.	O
</s>
<s>
Rather	O
than	O
concatenating	O
the	O
segment	B-Device
register	B-General_Concept
with	O
the	O
address	B-General_Concept
register	I-General_Concept
,	O
as	O
in	O
most	O
processors	O
whose	O
address	O
space	O
exceeds	O
their	O
register	B-General_Concept
size	O
,	O
the	O
8086	B-General_Concept
shifts	O
the	O
16-bit	B-Device
segment	B-Device
only	O
four	O
bits	O
left	O
before	O
adding	O
it	O
to	O
the	O
16-bit	B-Device
offset	O
(	O
16×segment	O
+	O
offset	O
)	O
,	O
therefore	O
producing	O
a	B-Application
20-bit	O
external	O
(	O
or	O
effective	O
or	O
physical	O
)	O
address	O
from	O
the	O
32-bit	O
segment:offset	B-Device
pair	O
.	O
</s>
<s>
As	O
a	B-Application
result	O
,	O
each	O
external	O
address	O
can	O
be	O
referred	O
to	O
by	O
212	O
=	O
4096	O
different	O
segment:offset	B-Device
pairs	O
.	O
</s>
<s>
Although	O
considered	O
complicated	O
and	O
cumbersome	O
by	O
many	O
programmers	O
,	O
this	O
scheme	O
also	O
has	O
advantages	O
;	O
a	B-Application
small	O
program	O
(	O
less	O
than	O
64KB	O
)	O
can	O
be	O
loaded	O
starting	O
at	O
a	B-Application
fixed	O
offset	O
(	O
such	O
as	O
0000	O
)	O
in	O
its	O
own	O
segment	B-Device
,	O
avoiding	O
the	O
need	O
for	O
relocation	B-Library
,	O
with	O
at	O
most	O
15bytes	O
of	O
alignment	O
waste	O
.	O
</s>
<s>
Compilers	O
for	O
the	O
8086	B-General_Concept
family	O
commonly	O
support	O
two	O
types	O
of	O
pointer	O
,	O
near	O
and	O
far	O
.	O
</s>
<s>
Near	O
pointers	O
are	O
16-bit	B-Device
offsets	O
implicitly	O
associated	O
with	O
the	O
program	O
's	O
code	O
or	O
data	O
segment	B-Device
and	O
so	O
can	O
be	O
used	O
only	O
within	O
parts	O
of	O
a	B-Application
program	O
small	O
enough	O
to	O
fit	O
in	O
one	O
segment	B-Device
.	O
</s>
<s>
Far	O
pointers	O
are	O
32-bit	O
segment:offset	B-Device
pairs	O
resolving	O
to	O
20-bit	O
external	O
addresses	O
.	O
</s>
<s>
Some	O
compilers	O
also	O
support	O
huge	O
pointers	O
,	O
which	O
are	O
like	O
far	O
pointers	O
except	O
that	O
pointer	O
arithmetic	O
on	O
a	B-Application
huge	O
pointer	O
treats	O
it	O
as	O
a	B-Application
linear	O
20-bit	O
pointer	O
,	O
while	O
pointer	O
arithmetic	O
on	O
a	B-Application
far	O
pointer	O
wraps	B-Error_Name
around	I-Error_Name
within	O
its	O
16-bit	B-Device
offset	O
without	O
touching	O
the	O
segment	B-Device
part	O
of	O
the	O
address	O
.	O
</s>
<s>
The	O
tiny	O
model	O
means	O
that	O
code	O
and	O
data	O
are	O
shared	O
in	O
a	B-Application
single	O
segment	B-Device
,	O
just	O
as	O
in	O
most	O
8-bit	O
based	O
processors	O
,	O
and	O
can	O
be	O
used	O
to	O
build	O
.com	O
files	O
for	O
instance	O
.	O
</s>
<s>
the	O
designers	O
actually	O
contemplated	O
using	O
an	O
8-bit	O
shift	O
(	O
instead	O
of	O
4-bit	O
)	O
,	O
in	O
order	O
to	O
create	O
a	B-Application
16MB	O
physical	O
address	O
space	O
.	O
</s>
<s>
However	O
,	O
as	O
this	O
would	O
have	O
forced	O
segments	O
to	O
begin	O
on	O
256-byte	O
boundaries	O
,	O
and	O
1MB	O
was	O
considered	O
very	O
large	O
for	O
a	B-Application
microprocessor	B-Architecture
around	O
1976	O
,	O
the	O
idea	O
was	O
dismissed	O
.	O
</s>
<s>
Also	O
,	O
there	O
were	O
not	O
enough	O
pins	O
available	O
on	O
a	B-Application
low	O
cost	O
40-pin	O
package	O
for	O
the	O
additional	O
four	O
address	O
bus	O
pins	O
.	O
</s>
<s>
In	O
principle	O
,	O
the	O
address	O
space	O
of	O
the	O
x86	B-Operating_System
series	O
could	O
have	O
been	O
extended	O
in	O
later	O
processors	O
by	O
increasing	O
the	O
shift	O
value	O
,	O
as	O
long	O
as	O
applications	O
obtained	O
their	O
segments	O
from	O
the	O
operating	O
system	O
and	O
did	O
not	O
make	O
assumptions	O
about	O
the	O
equivalence	O
of	O
different	O
segment:offset	B-Device
pairs	O
.	O
</s>
<s>
In	O
practice	O
the	O
use	O
of	O
"	O
huge	O
"	O
pointers	O
and	O
similar	O
mechanisms	O
was	O
widespread	O
and	O
the	O
flat	O
32-bit	O
addressing	O
made	O
possible	O
with	O
the	O
32-bit	O
offset	O
registers	B-General_Concept
in	O
the	O
80386	B-General_Concept
eventually	O
extended	O
the	O
limited	O
addressing	O
range	O
in	O
a	B-Application
more	O
general	O
way	O
.	O
</s>
<s>
The	O
instruction	O
stream	O
is	O
fetched	O
from	O
memory	O
as	O
words	O
and	O
is	O
addressed	O
internally	O
by	O
the	O
processor	O
to	O
the	O
byte	B-Application
level	O
as	O
necessary	O
.	O
</s>
<s>
An	O
instruction	O
stream	O
queuing	O
mechanism	O
allows	O
up	O
to	O
6	O
bytes	B-Application
of	O
the	O
instruction	O
stream	O
to	O
be	O
queued	O
while	O
waiting	O
for	O
decoding	O
and	O
execution	O
.	O
</s>
<s>
The	O
queue	O
acts	O
as	O
a	B-Application
First-In-First-Out	O
(	O
FIFO	O
)	O
buffer	O
,	O
from	O
which	O
the	O
Execution	O
Unit	O
(	O
EU	O
)	O
extracts	O
instruction	O
bytes	B-Application
as	O
required	O
.	O
</s>
<s>
Whenever	O
there	O
is	O
space	O
for	O
at	O
least	O
two	O
bytes	B-Application
in	O
the	O
queue	O
,	O
the	O
BIU	O
will	O
attempt	O
a	B-Application
word	O
fetch	O
memory	O
cycle	O
.	O
</s>
<s>
If	O
the	O
queue	O
is	O
empty	O
(	O
following	O
a	B-Application
branch	O
instruction	O
,	O
for	O
example	O
)	O
,	O
the	O
first	O
byte	B-Application
into	O
the	O
queue	O
immediately	O
becomes	O
available	O
to	O
the	O
EU	O
.	O
</s>
<s>
Small	O
programs	O
could	O
ignore	O
the	O
segmentation	O
and	O
just	O
use	O
plain	O
16-bit	B-Device
addressing	O
.	O
</s>
<s>
This	O
allows	O
8-bit	O
software	O
to	O
be	O
quite	O
easily	O
ported	O
to	O
the	O
8086	B-General_Concept
.	O
</s>
<s>
The	O
authors	O
of	O
most	O
DOS	B-Device
implementations	O
took	O
advantage	O
of	O
this	O
by	O
providing	O
an	O
Application	B-Application
Programming	I-Application
Interface	I-Application
very	O
similar	O
to	O
CP/M	B-Application
as	O
well	O
as	O
including	O
the	O
simple	O
.com	O
executable	O
file	O
format	O
,	O
identical	O
to	O
CP/M	B-Application
.	O
</s>
<s>
This	O
was	O
important	O
when	O
the	O
8086	B-General_Concept
and	O
MS-DOS	O
were	O
new	O
,	O
because	O
it	O
allowed	O
many	O
existing	O
CP/M	B-Application
(	O
and	O
other	O
)	O
applications	O
to	O
be	O
quickly	O
made	O
available	O
,	O
greatly	O
easing	O
acceptance	O
of	O
the	O
new	O
platform	O
.	O
</s>
<s>
The	O
following	O
8086/8088	O
assembler	B-Language
source	O
code	O
is	O
for	O
a	B-Application
subroutine	O
named	O
_memcpy	O
that	O
copies	O
a	B-Application
block	O
of	O
data	O
bytes	B-Application
of	O
a	B-Application
given	O
size	O
from	O
one	O
location	O
to	O
another	O
.	O
</s>
<s>
The	O
data	O
block	O
is	O
copied	O
one	O
byte	B-Application
at	O
a	B-Application
time	O
,	O
and	O
the	O
data	O
movement	O
and	O
looping	O
logic	O
utilizes	O
16-bit	B-Device
operations	O
.	O
</s>
<s>
;	O
Copy	O
a	B-Application
block	O
of	O
memory	O
from	O
one	O
location	O
to	O
another	O
.	O
</s>
<s>
The	O
code	O
above	O
uses	O
the	O
BP	O
(	O
base	O
pointer	O
)	O
register	B-General_Concept
to	O
establish	O
a	B-Application
call	O
frame	O
,	O
an	O
area	O
on	O
the	O
stack	B-Application
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
,	O
and	O
has	O
been	O
used	O
by	O
most	O
ALGOL-like	B-Language
languages	O
since	O
the	O
late	O
1950s	O
.	O
</s>
<s>
The	O
above	O
routine	O
is	O
a	B-Application
rather	O
cumbersome	O
way	O
to	O
copy	O
blocks	O
of	O
data	O
.	O
</s>
<s>
The	O
8086	B-General_Concept
provides	O
dedicated	O
instructions	O
for	O
copying	O
strings	O
of	O
bytes	B-Application
.	O
</s>
<s>
These	O
instructions	O
assume	O
that	O
the	O
source	O
data	O
is	O
stored	O
at	O
DS:SI	O
,	O
the	O
destination	O
data	O
is	O
stored	O
at	O
ES:DI	O
,	O
and	O
that	O
the	O
number	O
of	O
elements	O
to	O
copy	O
is	O
stored	O
in	O
CX	O
.	O
</s>
<s>
The	O
above	O
routine	O
requires	O
the	O
source	O
and	O
the	O
destination	O
block	O
to	O
be	O
in	O
the	O
same	O
segment	B-Device
,	O
therefore	O
DS	O
is	O
copied	O
to	O
ES	O
.	O
</s>
<s>
This	O
copies	O
the	O
block	O
of	O
data	O
one	O
byte	B-Application
at	O
a	B-Application
time	O
.	O
</s>
<s>
The	O
REP	O
instruction	O
causes	O
the	O
following	O
MOVSB	O
to	O
repeat	O
until	O
CX	O
is	O
zero	O
,	O
automatically	O
incrementing	O
SI	B-General_Concept
and	O
DI	O
and	O
decrementing	O
CX	O
as	O
it	O
repeats	O
.	O
</s>
<s>
Alternatively	O
the	O
MOVSW	O
instruction	O
can	O
be	O
used	O
to	O
copy	O
16-bit	B-Device
words	O
(	O
double	O
bytes	B-Application
)	O
at	O
a	B-Application
time	O
(	O
in	O
which	O
case	O
CX	O
counts	O
the	O
number	O
of	O
words	O
copied	O
instead	O
of	O
the	O
number	O
of	O
bytes	B-Application
)	O
.	O
</s>
<s>
Most	O
assemblers	B-Language
will	O
properly	O
recognize	O
the	O
REP	O
instruction	O
if	O
used	O
as	O
an	O
in-line	O
prefix	O
to	O
the	O
MOVSB	O
instruction	O
,	O
as	O
in	O
REP	O
MOVSB	O
.	O
</s>
<s>
This	O
routine	O
will	O
operate	O
correctly	O
if	O
interrupted	O
,	O
because	O
the	O
program	B-General_Concept
counter	I-General_Concept
will	O
continue	O
to	O
point	O
to	O
the	O
REP	O
instruction	O
until	O
the	O
block	O
copy	O
is	O
completed	O
.	O
</s>
<s>
The	O
copy	O
will	O
therefore	O
continue	O
from	O
where	O
it	O
left	O
off	O
when	O
the	O
interrupt	B-Application
service	O
routine	O
returns	O
control	O
.	O
</s>
<s>
Although	O
partly	O
shadowed	O
by	O
other	O
design	O
choices	O
in	O
this	O
particular	O
chip	O
,	O
the	O
multiplexed	B-Architecture
address	O
and	O
data	B-General_Concept
buses	I-General_Concept
limit	O
performance	O
slightly	O
;	O
transfers	O
of	O
16-bit	B-Device
or	O
8-bit	O
quantities	O
are	O
done	O
in	O
a	B-Application
four-clock	O
memory	O
access	O
cycle	O
,	O
which	O
is	O
faster	O
on	O
16-bit	B-Device
,	O
although	O
slower	O
on	O
8-bit	O
quantities	O
,	O
compared	O
to	O
many	O
contemporary	O
8-bit	O
based	O
CPUs	O
.	O
</s>
<s>
As	O
instructions	O
vary	O
from	O
one	O
to	O
six	O
bytes	B-Application
,	O
fetch	O
and	O
execution	O
are	O
made	O
concurrent	B-Operating_System
and	O
decoupled	O
into	O
separate	O
units	O
(	O
as	O
it	O
remains	O
in	O
today	O
's	O
x86	B-Operating_System
processors	O
)	O
:	O
The	O
bus	O
interface	O
unit	O
feeds	O
the	O
instruction	O
stream	O
to	O
the	O
execution	O
unit	O
through	O
a	B-Application
6-byte	O
prefetch	O
queue	O
(	O
a	B-Application
form	O
of	O
loosely	O
coupled	O
pipelining	B-General_Concept
)	O
,	O
speeding	O
up	O
operations	O
on	O
registers	B-General_Concept
and	O
immediates	O
,	O
while	O
memory	O
operations	O
became	O
slower	O
(	O
four	O
years	O
later	O
,	O
this	O
performance	O
problem	O
was	O
fixed	O
with	O
the	O
80186	B-Device
and	O
80286	B-General_Concept
)	O
.	O
</s>
<s>
However	O
,	O
the	O
full	O
(	O
instead	O
of	O
partial	O
)	O
16-bit	B-Device
architecture	I-Device
with	O
a	B-Application
full	O
width	O
ALU	B-General_Concept
meant	O
that	O
16-bit	B-Device
arithmetic	O
instructions	O
could	O
now	O
be	O
performed	O
with	O
a	B-Application
single	O
ALU	B-General_Concept
cycle	O
(	O
instead	O
of	O
two	O
,	O
via	O
internal	O
carry	O
,	O
as	O
in	O
the	O
8080	B-General_Concept
and	O
8085	B-General_Concept
)	O
,	O
speeding	O
up	O
such	O
instructions	O
considerably	O
.	O
</s>
<s>
Combined	O
with	O
orthogonalizations	O
of	O
operations	O
versus	O
operand	O
types	O
and	O
addressing	B-Language
modes	I-Language
,	O
as	O
well	O
as	O
other	O
enhancements	O
,	O
this	O
made	O
the	O
performance	O
gain	O
over	O
the	O
8080	B-General_Concept
or	O
8085	B-General_Concept
fairly	O
significant	O
,	O
despite	O
cases	O
where	O
the	O
older	O
chips	O
may	O
be	O
faster	O
(	O
see	O
below	O
)	O
.	O
</s>
<s>
+	O
Execution	O
times	O
for	O
typical	O
instructions	O
(	O
in	O
clock	O
cycles	O
)	O
(	O
Similarly	O
for	O
iAPX	B-General_Concept
286	I-General_Concept
,	O
80386	B-General_Concept
,	O
80387	O
.	O
)	O
</s>
<s>
EA	O
=	O
time	O
to	O
compute	O
effective	B-Language
address	I-Language
,	O
ranging	O
from	O
5	O
to	O
12	O
cycles	O
.	O
</s>
<s>
As	O
can	O
be	O
seen	O
from	O
these	O
tables	O
,	O
operations	O
on	O
registers	B-General_Concept
and	O
immediates	O
were	O
fast	O
(	O
between	O
2	O
and	O
4	O
cycles	O
)	O
,	O
while	O
memory-operand	O
instructions	O
and	O
jumps	O
were	O
quite	O
slow	O
;	O
jumps	O
took	O
more	O
cycles	O
than	O
on	O
the	O
simple	O
8080	B-General_Concept
and	O
8085	B-General_Concept
,	O
and	O
the	O
8088	B-Device
(	O
used	O
in	O
the	O
IBM	B-Device
PC	I-Device
)	O
was	O
additionally	O
hampered	O
by	O
its	O
narrower	O
bus	O
.	O
</s>
<s>
No	O
dedicated	O
address	O
calculation	O
adder	O
was	O
afforded	O
;	O
the	O
microcode	B-Device
routines	O
had	O
to	O
use	O
the	O
main	O
ALU	B-General_Concept
for	O
this	O
(	O
although	O
there	O
was	O
a	B-Application
dedicated	O
segment	B-Device
+	O
offset	O
adder	O
)	O
.	O
</s>
<s>
The	O
address	O
and	O
data	B-General_Concept
buses	I-General_Concept
were	O
multiplexed	B-Architecture
,	O
forcing	O
a	B-Application
slightly	O
longer	O
(	O
33	O
~	O
50%	O
)	O
bus	O
cycle	O
than	O
in	O
typical	O
contemporary	O
8-bit	O
processors	O
.	O
</s>
<s>
However	O
,	O
memory	O
access	O
performance	O
was	O
drastically	O
enhanced	O
with	O
Intel	O
's	O
next	O
generation	O
of	O
8086	B-General_Concept
family	O
CPUs	O
.	O
</s>
<s>
The	O
80186	B-Device
and	O
80286	B-General_Concept
both	O
had	O
dedicated	O
address	O
calculation	O
hardware	B-Architecture
,	O
saving	O
many	O
cycles	O
,	O
and	O
the	O
80286	B-General_Concept
also	O
had	O
separate	O
(	O
non-multiplexed	O
)	O
address	O
and	O
data	B-General_Concept
buses	I-General_Concept
.	O
</s>
<s>
The	O
8086/8088	O
could	O
be	O
connected	O
to	O
a	B-Application
mathematical	O
coprocessor	B-General_Concept
to	O
add	O
hardware/microcode	O
-based	O
floating-point	B-Algorithm
performance	O
.	O
</s>
<s>
The	O
Intel	B-Device
8087	I-Device
was	O
the	O
standard	O
math	O
coprocessor	B-General_Concept
for	O
the	O
8086	B-General_Concept
and	O
8088	B-Device
,	O
operating	O
on	O
80-bit	O
numbers	O
.	O
</s>
<s>
Manufacturers	O
like	O
Cyrix	O
(	O
8087-compatible	O
)	O
and	O
Weitek	O
(	O
not	O
8087-compatible	O
)	O
eventually	O
came	O
up	O
with	O
high-performance	O
floating-point	B-Algorithm
coprocessors	B-General_Concept
that	O
competed	O
with	O
the	O
8087	B-Device
.	O
</s>
<s>
HMOS-III	O
and	O
CMOS	B-Device
versions	O
were	O
manufactured	O
for	O
a	B-Application
long	O
time	O
(	O
at	O
least	O
a	B-Application
while	O
into	O
the	O
1990s	O
)	O
for	O
embedded	B-Architecture
systems	I-Architecture
,	O
although	O
its	O
successor	O
,	O
the	O
80186/80188	B-Device
(	O
which	O
includes	O
some	O
on-chip	O
peripherals	O
)	O
,	O
has	O
been	O
more	O
popular	O
for	O
embedded	O
use	O
.	O
</s>
<s>
The	O
80C86	O
,	O
the	O
CMOS	B-Device
version	O
of	O
the	O
8086	B-General_Concept
,	O
was	O
used	O
in	O
the	O
GRiDPad	B-Device
,	O
Toshiba	B-Device
T1200	I-Device
,	O
HP	B-Device
110	I-Device
,	O
and	O
finally	O
the	O
1998	O
–	O
1999	O
Lunar	O
Prospector	O
.	O
</s>
<s>
For	O
the	O
packaging	O
,	O
the	O
Intel	B-General_Concept
8086	I-General_Concept
was	O
available	O
both	O
in	O
ceramic	O
and	O
plastic	O
DIP	B-Algorithm
packages	O
.	O
</s>
<s>
8086	B-General_Concept
5	O
MHz	O
HMOS	O
0	O
°C	O
to	O
70	O
°C	O
June	O
8	O
,	O
1978	O
$86.65	O
8086-1	B-General_Concept
10	O
MHz	O
HMOS	O
II	O
Commercial	O
8086-2	B-General_Concept
8	O
MHz	O
HMOS	O
II	O
Commercial	O
January/February	O
1980	O
$200	O
8086-4	B-General_Concept
4	O
MHz	O
HMOS	O
Commercial	O
$72.50	O
Price	O
reduced	O
by	O
21%	O
from	O
USD	O
$99.00	O
,	O
no	O
information	O
in	O
quantity	O
value	O
listed	O
.	O
</s>
<s>
I8086	B-General_Concept
5	O
MHz	O
HMOS	O
Industrial	O
−40	O
°C	O
to	O
+85	O
°C	O
May/June	O
1980	O
$173.25	O
M8086	B-General_Concept
5	O
MHz	O
HMOS	O
Military	O
grade	O
−55	O
°C	O
to	O
+125	O
°C	O
80C86Intel	O
Corporation	O
,	O
"	O
NewsBit	O
:	O
Intel	O
Licenses	O
Oki	O
on	O
CMOS	B-Device
Version	O
of	O
Several	O
Products	O
"	O
,	O
Solutions	O
,	O
July/August	O
1984	O
,	O
Page	O
1	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
NEC	B-Device
V20	I-Device
and	O
NEC	B-Device
V30	I-Device
pair	O
were	O
hardware-compatible	O
with	O
the	O
8088	B-Device
and	O
8086	B-General_Concept
even	O
though	O
NEC	O
made	O
original	O
Intel	B-Operating_System
clones	I-Operating_System
μPD8088D	O
and	O
μPD8086D	O
respectively	O
,	O
but	O
incorporated	O
the	O
instruction	B-General_Concept
set	I-General_Concept
of	O
the	O
80186	B-Device
along	O
with	O
some	O
(	O
but	O
not	O
all	O
)	O
of	O
the	O
80186	B-Device
speed	O
enhancements	O
,	O
providing	O
a	B-Application
drop-in	O
capability	O
to	O
upgrade	O
both	O
instruction	B-General_Concept
set	I-General_Concept
and	O
processing	O
speed	O
without	O
manufacturers	O
having	O
to	O
modify	O
their	O
designs	O
.	O
</s>
<s>
Such	O
relatively	O
simple	O
and	O
low-power	O
8086-compatible	O
processors	O
in	O
CMOS	B-Device
are	O
still	O
used	O
in	O
embedded	B-Architecture
systems	I-Architecture
.	O
</s>
<s>
The	O
electronics	O
industry	O
of	O
the	O
Soviet	O
Union	O
was	O
able	O
to	O
replicate	O
the	O
8086	B-General_Concept
through	O
.	O
</s>
<s>
The	O
resulting	O
chip	O
,	O
K1810VM86	B-Device
,	O
was	O
binary	O
and	O
pin-compatible	O
with	O
the	O
8086	B-General_Concept
.	O
</s>
<s>
i8086	B-General_Concept
and	O
i8088	B-Device
were	O
respectively	O
the	O
cores	O
of	O
the	O
Soviet-made	O
PC-compatible	O
EC1831	O
and	O
EC1832	O
desktops	O
.	O
</s>
<s>
However	O
,	O
the	O
EC1831	O
computer	O
(	O
IZOT	O
1036C	O
)	O
had	O
significant	O
hardware	B-Architecture
differences	O
from	O
the	O
IBM	B-Device
PC	I-Device
prototype	O
.	O
</s>
<s>
Later	O
some	O
of	O
the	O
EC1831	O
principles	O
were	O
adopted	O
in	O
PS/2	B-Device
(	O
US	O
Pat	O
.	O
</s>
<s>
GB-A-2211325	O
,	O
Published	O
June	O
28	O
,	O
1989	O
)	O
.	O
</s>
<s>
Intel	B-Device
8255	I-Device
:	O
programmable	O
peripheral	O
interface	O
,	O
3x	O
8-bit	O
I/O	O
pins	O
used	O
for	O
printer	O
connection	O
etc	O
.	O
</s>
<s>
The	O
Intel	O
Multibus-compatible	O
single-board	B-Device
computer	I-Device
ISBC	B-Device
86/12	O
was	O
announced	O
in	O
1978	O
.	O
</s>
<s>
The	O
Xerox	B-Device
NoteTaker	I-Device
was	O
one	O
of	O
the	O
earliest	O
portable	B-Device
computer	I-Device
designs	O
in	O
1978	O
and	O
used	O
three	O
8086	B-General_Concept
chips	O
(	O
as	O
CPU	B-General_Concept
,	O
graphics	O
processor	O
,	O
and	O
I/O	O
processor	O
)	O
,	O
but	O
never	O
entered	O
commercial	O
production	O
.	O
</s>
<s>
Seattle	O
Computer	O
Products	O
shipped	O
S-100	B-Architecture
bus	I-Architecture
based	O
8086	B-General_Concept
systems	O
(	O
SCP200B	O
)	O
as	O
early	O
as	O
November	O
1979	O
.	O
</s>
<s>
One	O
of	O
the	O
most	O
influential	O
microcomputers	O
of	O
all	O
,	O
the	O
IBM	B-Device
PC	I-Device
,	O
used	O
the	O
Intel	B-Device
8088	I-Device
,	O
a	B-Application
version	O
of	O
the	O
8086	B-General_Concept
with	O
an	O
8-bit	O
data	B-General_Concept
bus	I-General_Concept
(	O
as	O
mentioned	O
above	O
)	O
.	O
</s>
<s>
The	O
first	O
Compaq	B-Device
Deskpro	I-Device
used	O
an	O
8086	B-General_Concept
running	O
at	O
7.16MHz	O
,	O
but	O
was	O
compatible	O
with	O
add-in	O
cards	O
designed	O
for	O
the	O
4.77MHz	O
IBM	B-Device
PC	I-Device
XT	I-Device
and	O
could	O
switch	O
the	O
CPU	B-General_Concept
down	O
to	O
the	O
lower	O
speed	O
(	O
which	O
also	O
switched	O
in	O
a	B-Application
memory	O
bus	O
buffer	O
to	O
simulate	O
the	O
8088	B-Device
's	O
slower	O
access	O
)	O
to	O
avoid	O
software	O
timing	O
issues	O
.	O
</s>
<s>
An	O
8MHz	O
8086-2	B-General_Concept
was	O
used	O
in	O
the	O
AT&T	B-Operating_System
6300	I-Operating_System
PC	I-Operating_System
(	O
built	O
by	O
Olivetti	O
,	O
and	O
known	O
globally	O
under	O
several	O
brands	O
and	O
model	O
numbers	O
)	O
,	O
an	O
IBM	O
PC-compatible	O
desktop	O
microcomputer	O
.	O
</s>
<s>
The	O
M24	O
/	O
PC	O
6300	O
has	O
IBM	B-Device
PC/XT	I-Device
compatible	O
8-bit	O
expansion	O
slots	O
,	O
but	O
some	O
of	O
them	O
have	O
a	B-Application
proprietary	O
extension	O
providing	O
the	O
full	O
16-bit	B-Device
data	B-General_Concept
bus	I-General_Concept
of	O
the	O
8086	B-General_Concept
CPU	B-General_Concept
(	O
similar	O
in	O
concept	O
to	O
the	O
16-bit	B-Device
slots	O
of	O
the	O
IBM	B-Operating_System
PC	I-Operating_System
AT	I-Operating_System
,	O
but	O
different	O
in	O
the	O
design	O
details	O
,	O
and	O
physically	O
incompatible	O
)	O
,	O
and	O
all	O
system	O
peripherals	O
including	O
the	O
onboard	O
video	O
system	O
also	O
enjoy	O
16-bit	B-Device
data	O
transfers	O
.	O
</s>
<s>
The	O
later	O
Olivetti	O
M24SP	O
featured	O
an	O
8086-2	B-General_Concept
running	O
at	O
the	O
full	O
maximum	O
10MHz	O
.	O
</s>
<s>
The	O
IBM	B-Device
PS/2	I-Device
models	O
25	O
and	O
30	O
were	O
built	O
with	O
an	O
8MHz	O
8086	B-General_Concept
.	O
</s>
<s>
The	O
Amstrad	O
PC1512	O
,	O
PC1640	O
,	O
PC2086	O
,	O
PC3086	O
and	O
PC5086	O
all	O
used	O
8086	B-General_Concept
CPUs	O
at	O
8MHz	O
.	O
</s>
<s>
The	O
NEC	B-Operating_System
PC-9801	I-Operating_System
.	O
</s>
<s>
The	O
Tandy	O
1000	O
SL-series	O
and	O
RL	O
machines	O
used	O
9.47MHz	O
8086	B-General_Concept
CPUs	O
.	O
</s>
<s>
The	O
IBM	B-Protocol
Displaywriter	I-Protocol
word	O
processing	O
machine	O
and	O
the	O
Wang	O
Professional	O
Computer	O
,	O
manufactured	O
by	O
Wang	O
Laboratories	O
,	O
also	O
used	O
the	O
8086	B-General_Concept
.	O
</s>
<s>
NASA	O
used	O
original	O
8086	B-General_Concept
CPUs	O
on	O
equipment	O
for	O
ground-based	O
maintenance	O
of	O
the	O
Space	O
Shuttle	O
Discovery	O
until	O
the	O
end	O
of	O
the	O
space	O
shuttle	O
program	O
in	O
2011	O
.	O
</s>
<s>
This	O
decision	O
was	O
made	O
to	O
prevent	O
software	B-Error_Name
regression	I-Error_Name
that	O
might	O
result	O
from	O
upgrading	O
or	O
from	O
switching	O
to	O
imperfect	O
clones	O
.	O
</s>
<s>
The	O
Tektronix	O
4170	O
ran	O
CP/M	B-Operating_System
-86	I-Operating_System
and	O
used	O
an	O
8086	B-General_Concept
.	O
</s>
