<s>
The	O
Intel	B-General_Concept
80286	I-General_Concept
(	O
also	O
marketed	O
as	O
the	O
iAPX	B-General_Concept
286	I-General_Concept
and	O
often	O
called	O
Intel	B-General_Concept
286	I-General_Concept
)	O
is	O
a	O
16-bit	B-Device
microprocessor	B-Architecture
that	O
was	O
introduced	O
on	O
February	O
1	O
,	O
1982	O
.	O
</s>
<s>
It	O
was	O
the	O
first	O
8086-based	O
CPU	O
with	O
separate	O
,	O
non-multiplexed	O
address	B-Architecture
and	O
data	B-General_Concept
buses	I-General_Concept
and	O
also	O
the	O
first	O
with	O
memory	B-General_Concept
management	I-General_Concept
and	O
wide	O
protection	O
abilities	O
.	O
</s>
<s>
The	O
80286	B-General_Concept
used	O
approximately	O
134,000	O
transistors	B-Application
in	O
its	O
original	O
nMOS	B-Algorithm
(	O
HMOS	B-Algorithm
)	O
incarnation	O
and	O
,	O
just	O
like	O
the	O
contemporary	O
80186	B-Device
,	O
it	O
could	O
correctly	O
execute	O
most	O
software	O
written	O
for	O
the	O
earlier	O
Intel	B-General_Concept
8086	I-General_Concept
and	O
8088	B-Device
processors	O
.	O
</s>
<s>
The	O
80286	B-General_Concept
was	O
employed	O
for	O
the	O
IBM	B-Operating_System
PC/AT	I-Operating_System
,	O
introduced	O
in	O
1984	O
,	O
and	O
then	O
widely	O
used	O
in	O
most	O
PC/AT	B-Operating_System
compatible	O
computers	O
until	O
the	O
early	O
1990s	O
.	O
</s>
<s>
In	O
1987	O
,	O
Intel	O
shipped	O
its	O
five-millionth	O
80286	B-General_Concept
microprocessor	I-General_Concept
.	O
</s>
<s>
Intel	O
's	O
first	O
80286	B-General_Concept
chips	O
were	O
specified	O
for	O
a	O
maximum	O
clockrate	O
of	O
5	O
,	O
6	O
or	O
8MHz	O
and	O
later	O
releases	O
for	O
12.5MHz	O
.	O
</s>
<s>
Intersil	O
and	O
Fujitsu	O
also	O
designed	O
fully	O
static	O
CMOS	B-Device
versions	O
of	O
Intel	O
's	O
original	O
depletion-load	B-Algorithm
nMOS	I-Algorithm
implementation	O
,	O
largely	O
aimed	O
at	O
battery-powered	O
devices	O
.	O
</s>
<s>
On	O
average	O
,	O
the	O
80286	B-General_Concept
was	O
reportedly	O
measured	O
to	O
have	O
a	O
speed	O
of	O
about	O
0.21	O
instructions	O
per	O
clock	O
on	O
"	O
typical	O
"	O
programs	O
,	O
although	O
it	O
could	O
be	O
significantly	O
faster	O
on	O
optimized	O
code	O
and	O
in	O
tight	O
loops	O
,	O
as	O
many	O
instructions	O
could	O
execute	O
in	O
2	O
clock	O
cycles	O
each	O
.	O
</s>
<s>
The	O
later	O
E-stepping	O
level	O
of	O
the	O
80286	B-General_Concept
was	O
free	O
of	O
the	O
several	O
significant	O
errata	O
that	O
caused	O
problems	O
for	O
programmers	O
and	O
operating-system	O
writers	O
in	O
the	O
earlier	O
B-step	O
and	O
C-step	O
CPUs	O
(	O
common	O
in	O
the	O
AT	O
and	O
AT	O
clones	O
)	O
.	O
</s>
<s>
This	O
E-2	O
stepping	B-General_Concept
part	O
may	O
have	O
been	O
available	O
in	O
later	O
1986	O
.	O
</s>
<s>
Intel	O
second	O
sourced	O
this	O
microprocessor	B-Architecture
to	O
Fujitsu	O
Limited	O
around	O
1985	O
.	O
</s>
<s>
80286-10Intel	O
Corporation	O
,	O
"	O
New	O
Product	O
Focus	O
Components	O
:	O
80286	B-General_Concept
Workhorses	O
:	O
Twice	O
As	O
Fast	O
"	O
,	O
Solutions	O
,	O
July/August	O
1985	O
,	O
Page	O
17	O
.	O
</s>
<s>
10	O
MHz	O
HMOS-III	O
1.5	O
μm	O
July/August	O
1985	O
$155	O
80286-12	O
12.5	O
MHz	O
HMOS-III	O
1.5	O
μm	O
July/August	O
1985	O
$260	O
MG80286Intel	O
Corporation	O
,	O
"	O
New	O
Product	O
Focus	O
Components	O
:	O
Highest	O
Ranking	O
16-bit	B-Device
Microprocessor	B-Architecture
Meets	O
Military	O
Objectives	O
"	O
,	O
Solutions	O
,	O
September/October	O
1985	O
,	O
page	O
13	O
.	O
</s>
<s>
Intel	O
did	O
not	O
expect	O
personal	O
computers	O
to	O
use	O
the	O
286	B-General_Concept
.	O
</s>
<s>
The	O
CPU	O
was	O
designed	O
for	O
multi-user	B-Operating_System
systems	I-Operating_System
with	O
multitasking	B-Operating_System
applications	O
,	O
including	O
communications	O
(	O
such	O
as	O
automated	O
PBXs	B-Device
)	O
and	O
real-time	B-General_Concept
process	O
control	O
.	O
</s>
<s>
It	O
had	O
134,000	O
transistors	B-Application
and	O
consisted	O
of	O
four	O
independent	O
units	O
:	O
the	O
address	B-Architecture
unit	O
,	O
bus	O
unit	O
,	O
instruction	O
unit	O
,	O
and	O
execution	O
unit	O
,	O
organized	O
into	O
a	O
loosely	B-Application
coupled	I-Application
(	O
buffered	O
)	O
pipeline	B-General_Concept
,	O
just	O
as	O
in	O
the	O
8086	B-General_Concept
.	O
</s>
<s>
It	O
was	O
produced	O
in	O
a	O
68-pin	O
package	O
,	O
including	O
PLCC	B-Algorithm
(	O
plastic	B-Algorithm
leaded	I-Algorithm
chip	I-Algorithm
carrier	I-Algorithm
)	O
,	O
LCC	O
(	O
leadless	O
chip	B-Algorithm
carrier	I-Algorithm
)	O
and	O
PGA	B-Algorithm
(	O
pin	B-Algorithm
grid	I-Algorithm
array	I-Algorithm
)	O
packages	O
.	O
</s>
<s>
The	O
performance	O
increase	O
of	O
the	O
80286	B-General_Concept
over	O
the	O
8086	B-General_Concept
(	O
or	O
8088	B-Device
)	O
could	O
be	O
more	O
than	O
100%	O
per	O
clock	O
cycle	O
in	O
many	O
programs	O
(	O
i.e.	O
,	O
a	O
doubled	O
performance	O
at	O
the	O
same	O
clock	O
speed	O
)	O
.	O
</s>
<s>
This	O
was	O
a	O
large	O
increase	O
,	O
fully	O
comparable	O
to	O
the	O
speed	O
improvements	O
seven	O
years	O
later	O
when	O
the	O
i486	B-General_Concept
(	O
1989	O
)	O
or	O
the	O
original	B-General_Concept
Pentium	I-General_Concept
(	O
1993	O
)	O
were	O
introduced	O
.	O
</s>
<s>
This	O
was	O
partly	O
due	O
to	O
the	O
non-multiplexed	O
address	B-Architecture
and	O
data	B-General_Concept
buses	I-General_Concept
,	O
but	O
mainly	O
to	O
the	O
fact	O
that	O
address	B-Architecture
calculations	O
(	O
such	O
as	O
base+index	O
)	O
were	O
less	O
expensive	O
.	O
</s>
<s>
They	O
were	O
performed	O
by	O
a	O
dedicated	O
unit	O
in	O
the	O
80286	B-General_Concept
,	O
while	O
the	O
older	O
8086	B-General_Concept
had	O
to	O
do	O
effective	O
address	B-Architecture
computation	O
using	O
its	O
general	O
ALU	B-General_Concept
,	O
consuming	O
several	O
extra	O
clock	O
cycles	O
in	O
many	O
cases	O
.	O
</s>
<s>
Also	O
,	O
the	O
80286	B-General_Concept
was	O
more	O
efficient	O
in	O
the	O
prefetch	O
of	O
instructions	O
,	O
buffering	O
,	O
execution	O
of	O
jumps	O
,	O
and	O
in	O
complex	O
microcoded	B-Device
numerical	O
operations	O
such	O
as	O
MUL/DIV	O
than	O
its	O
predecessor	O
.	O
</s>
<s>
The	O
80286	B-General_Concept
included	O
,	O
in	O
addition	O
to	O
all	O
of	O
the	O
8086	B-General_Concept
instructions	O
,	O
all	O
of	O
the	O
new	O
instructions	O
of	O
the	O
80186	B-Device
:	O
ENTER	O
,	O
LEAVE	O
,	O
BOUND	O
,	O
INS	O
,	O
OUTS	O
,	O
PUSHA	O
,	O
POPA	O
,	O
PUSH	O
immediate	O
,	O
IMUL	O
immediate	O
,	O
and	O
immediate	O
shifts	O
and	O
rotates	O
.	O
</s>
<s>
The	O
80286	B-General_Concept
also	O
added	O
new	O
instructions	O
for	O
protected	B-Application
mode	I-Application
:	O
ARPL	O
,	O
CLTS	O
,	O
LAR	O
,	O
LGDT	O
,	O
LIDT	O
,	O
LLDT	O
,	O
LMSW	O
,	O
LSL	O
,	O
LTR	O
,	O
SGDT	O
,	O
SIDT	O
,	O
SLDT	O
,	O
SMSW	O
,	O
STR	O
,	O
VERR	O
,	O
and	O
VERW	O
.	O
</s>
<s>
Some	O
of	O
the	O
instructions	O
for	O
protected	B-Application
mode	I-Application
can	O
(	O
or	O
must	O
)	O
be	O
used	O
in	O
real	B-Application
mode	I-Application
to	O
set	O
up	O
and	O
switch	O
to	O
protected	B-Application
mode	I-Application
,	O
and	O
a	O
few	O
(	O
such	O
as	O
SMSW	O
and	O
LMSW	O
)	O
are	O
useful	O
for	O
real	B-Application
mode	I-Application
itself	O
.	O
</s>
<s>
The	O
Intel	B-General_Concept
80286	I-General_Concept
had	O
a	O
24-bit	O
address	B-Architecture
bus	I-Architecture
and	O
as	O
such	O
had	O
a	O
16MB	O
physical	O
address	B-General_Concept
space	I-General_Concept
,	O
compared	O
to	O
the	O
1MB	O
address	B-General_Concept
space	I-General_Concept
of	O
prior	O
x86	B-Operating_System
processors	O
.	O
</s>
<s>
It	O
was	O
the	O
first	O
x86	B-Operating_System
processor	O
to	O
support	O
virtual	B-Architecture
memory	I-Architecture
supporting	O
up	O
to	O
1GB	O
via	O
segmentation	O
.	O
</s>
<s>
However	O
,	O
memory	O
cost	O
and	O
the	O
initial	O
rarity	O
of	O
software	O
using	O
the	O
memory	O
above	O
1MB	O
meant	O
that	O
until	O
late	O
in	O
its	O
production	O
80286	B-General_Concept
computers	O
rarely	O
shipped	O
with	O
more	O
than	O
one	O
megabyte	O
of	O
RAM	O
.	O
</s>
<s>
Additionally	O
,	O
there	O
was	O
a	O
performance	O
penalty	O
involved	O
in	O
accessing	O
extended	B-Device
memory	I-Device
from	O
real	B-Application
mode	I-Application
as	O
noted	O
below	O
.	O
</s>
<s>
The	O
286	B-General_Concept
was	O
the	O
first	O
of	O
the	O
x86	B-Operating_System
CPU	O
family	O
to	O
support	O
protected	O
virtual-address	O
mode	O
,	O
commonly	O
called	O
"	O
protected	B-Application
mode	I-Application
"	O
.	O
</s>
<s>
In	O
addition	O
,	O
it	O
was	O
the	O
first	O
commercially	O
available	O
microprocessor	B-Architecture
with	O
on-chip	O
MMU	B-General_Concept
capabilities	O
(	O
systems	O
using	O
the	O
contemporaneous	O
Motorola	B-Device
68010	I-Device
and	O
NS320xx	B-Device
could	O
be	O
equipped	O
with	O
an	O
optional	O
MMU	B-General_Concept
controller	O
)	O
.	O
</s>
<s>
This	O
would	O
allow	O
IBM	O
compatibles	O
to	O
have	O
advanced	O
multitasking	B-Operating_System
OSes	O
for	O
the	O
first	O
time	O
and	O
compete	O
in	O
the	O
Unix-dominated	O
server/workstation	O
market	O
.	O
</s>
<s>
Several	O
additional	O
instructions	O
were	O
introduced	O
in	O
the	O
protected	B-Application
mode	I-Application
of	O
80286	B-General_Concept
,	O
which	O
are	O
helpful	O
for	O
multitasking	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
.	O
</s>
<s>
Another	O
important	O
feature	O
of	O
80286	B-General_Concept
is	O
the	O
prevention	O
of	O
unauthorized	O
access	O
.	O
</s>
<s>
In	O
80286	B-General_Concept
(	O
and	O
in	O
its	O
co-processor	O
Intel	O
80287	O
)	O
,	O
arithmetic	O
operations	O
can	O
be	O
performed	O
on	O
the	O
following	O
different	O
types	O
of	O
numbers	O
:	O
</s>
<s>
floating-point	B-Algorithm
numbers	I-Algorithm
(	O
only	O
with	O
an	O
80287	O
)	O
.	O
</s>
<s>
By	O
design	O
,	O
the	O
286	B-General_Concept
could	O
not	O
revert	O
from	O
protected	B-Application
mode	I-Application
to	O
the	O
basic	O
8086-compatible	O
real	B-Application
address	I-Application
mode	I-Application
(	O
"	O
real	B-Application
mode	I-Application
"	O
)	O
without	O
a	O
hardware-initiated	O
reset	O
.	O
</s>
<s>
In	O
the	O
PC/AT	B-Operating_System
introduced	O
in	O
1984	O
,	O
IBM	O
added	O
external	O
circuitry	O
,	O
as	O
well	O
as	O
specialized	O
code	O
in	O
the	O
ROM	B-Operating_System
BIOS	I-Operating_System
and	O
the	O
8042	B-Device
peripheral	O
microcontroller	O
to	O
enable	O
software	O
to	O
cause	O
the	O
reset	O
,	O
allowing	O
real-mode	B-Application
reentry	O
while	O
retaining	O
active	O
memory	O
and	O
returning	O
control	O
to	O
the	O
program	O
that	O
initiated	O
the	O
reset	O
.	O
</s>
<s>
(	O
The	O
BIOS	B-Operating_System
is	O
necessarily	O
involved	O
because	O
it	O
obtains	O
control	O
directly	O
whenever	O
the	O
CPU	O
resets	O
.	O
)	O
</s>
<s>
In	O
theory	O
,	O
real-mode	B-Application
applications	O
could	O
be	O
directly	O
executed	O
in	O
16-bit	B-Device
protected	B-Application
mode	I-Application
if	O
certain	O
rules	O
(	O
newly	O
proposed	O
with	O
the	O
introduction	O
of	O
the	O
80286	B-General_Concept
)	O
were	O
followed	O
;	O
however	O
,	O
as	O
many	O
DOS	B-Device
programs	O
did	O
not	O
conform	O
to	O
those	O
rules	O
,	O
protected	B-Application
mode	I-Application
was	O
not	O
widely	O
used	O
until	O
the	O
appearance	O
of	O
its	O
successor	O
,	O
the	O
32-bit	O
Intel	B-General_Concept
80386	I-General_Concept
,	O
which	O
was	O
designed	O
to	O
go	O
back	O
and	O
forth	O
between	O
modes	O
easily	O
and	O
to	O
provide	O
an	O
emulation	B-Application
of	O
real	B-Application
mode	I-Application
within	O
protected	B-Application
mode	I-Application
.	O
</s>
<s>
When	O
Intel	O
designed	O
the	O
286	B-General_Concept
,	O
it	O
was	O
not	O
designed	O
to	O
be	O
able	O
to	O
multitask	O
real-mode	B-Application
applications	O
;	O
real	B-Application
mode	I-Application
was	O
intended	O
to	O
be	O
a	O
simple	O
way	O
for	O
a	O
bootstrap	O
loader	O
to	O
prepare	O
the	O
system	O
and	O
then	O
switch	O
to	O
protected	B-Application
mode	I-Application
;	O
essentially	O
,	O
in	O
protected	B-Application
mode	I-Application
the	O
80286	B-General_Concept
was	O
designed	O
to	O
be	O
a	O
new	O
processor	O
with	O
many	O
similarities	O
to	O
its	O
predecessors	O
,	O
while	O
real	B-Application
mode	I-Application
on	O
the	O
80286	B-General_Concept
was	O
offered	O
for	O
smaller-scale	O
systems	O
that	O
could	O
benefit	O
from	O
a	O
more	O
advanced	O
version	O
of	O
the	O
80186	B-Device
CPU	O
core	O
,	O
with	O
advantages	O
such	O
as	O
higher	O
clock	O
rates	O
,	O
faster	O
instruction	O
execution	O
(	O
measured	O
in	O
clock	O
cycles	O
)	O
,	O
and	O
unmultiplexed	O
buses	O
,	O
but	O
not	O
the	O
24-bit	O
(	O
16	O
MB	O
)	O
memory	O
space	O
.	O
</s>
<s>
To	O
support	O
protected	B-Application
mode	I-Application
,	O
new	O
instructions	O
have	O
been	O
added	O
:	O
ARPL	O
,	O
VERR	O
,	O
VERW	O
,	O
LAR	O
,	O
LSL	O
,	O
SMSW	O
,	O
SGDT	O
,	O
SIDT	O
,	O
SLDT	O
,	O
STR	O
,	O
LMSW	O
,	O
LGDT	O
,	O
LIDT	O
,	O
LLDT	O
,	O
LTR	O
,	O
CLTS	O
.	O
</s>
<s>
There	O
are	O
also	O
new	O
exceptions	O
(	O
internal	O
interrupts	O
)	O
:	O
invalid	O
opcode	O
,	O
coprocessor	O
not	O
available	O
,	O
double	O
fault	O
,	O
coprocessor	O
segment	O
overrun	O
,	O
stack	O
fault	O
,	O
segment	O
overrun/general	O
protection	O
fault	O
,	O
and	O
others	O
only	O
for	O
protected	B-Application
mode	I-Application
.	O
</s>
<s>
The	O
protected	B-Application
mode	I-Application
of	O
the	O
80286	B-General_Concept
was	O
not	O
routinely	O
utilized	O
in	O
PC	O
applications	O
until	O
many	O
years	O
after	O
its	O
release	O
,	O
in	O
part	O
because	O
of	O
the	O
high	O
cost	O
of	O
adding	O
extended	B-Device
memory	I-Device
to	O
a	O
PC	O
,	O
but	O
also	O
because	O
of	O
the	O
need	O
for	O
software	O
to	O
support	O
the	O
large	O
user	O
base	O
of	O
8086	B-General_Concept
PCs	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
1986	O
the	O
only	O
program	O
that	O
made	O
use	O
of	O
it	O
was	O
VDISK	B-Application
,	O
a	O
RAM	B-Application
disk	I-Application
driver	O
included	O
with	O
PC	B-Operating_System
DOS	I-Operating_System
3.0	O
and	O
3.1	O
.	O
</s>
<s>
A	O
DOS	B-Device
could	O
utilize	O
the	O
additional	O
RAM	O
available	O
in	O
protected	B-Application
mode	I-Application
(	O
extended	B-Device
memory	I-Device
)	O
either	O
via	O
a	O
BIOS	B-Operating_System
call	O
(	O
INT	O
15h	O
,	O
AH	O
=	O
87h	O
)	O
,	O
as	O
a	O
RAM	B-Application
disk	I-Application
,	O
or	O
as	O
emulation	B-Application
of	O
expanded	B-Device
memory	I-Device
.	O
</s>
<s>
The	O
difficulty	O
lay	O
in	O
the	O
incompatibility	O
of	O
older	O
real-mode	B-Application
DOS	B-Device
programs	O
with	O
protected	B-Application
mode	I-Application
.	O
</s>
<s>
In	O
protected	B-Application
mode	I-Application
,	O
memory	B-General_Concept
management	I-General_Concept
and	O
interrupt	O
handling	O
were	O
done	O
differently	O
than	O
in	O
real	B-Application
mode	I-Application
.	O
</s>
<s>
In	O
addition	O
,	O
DOS	B-Device
programs	O
typically	O
would	O
directly	O
access	O
data	O
and	O
code	O
segments	O
that	O
did	O
not	O
belong	O
to	O
them	O
,	O
as	O
real	B-Application
mode	I-Application
allowed	O
them	O
to	O
do	O
without	O
restriction	O
;	O
in	O
contrast	O
,	O
the	O
design	O
intent	O
of	O
protected	B-Application
mode	I-Application
was	O
to	O
prevent	O
programs	O
from	O
accessing	O
any	O
segments	O
other	O
than	O
their	O
own	O
unless	O
special	O
access	O
was	O
explicitly	O
allowed	O
.	O
</s>
<s>
While	O
it	O
was	O
possible	O
to	O
set	O
up	O
a	O
protected-mode	B-Application
environment	O
that	O
allowed	O
all	O
programs	O
access	O
to	O
all	O
segments	O
(	O
by	O
putting	O
all	O
segment	O
descriptors	O
into	O
the	O
GDT	O
and	O
assigning	O
them	O
all	O
the	O
same	O
privilege	O
level	O
)	O
,	O
this	O
undermined	O
nearly	O
all	O
of	O
the	O
advantages	O
of	O
protected	B-Application
mode	I-Application
except	O
the	O
extended	O
(	O
24-bit	O
)	O
address	B-General_Concept
space	I-General_Concept
.	O
</s>
<s>
The	O
choice	O
that	O
OS	O
developers	O
faced	O
was	O
either	O
to	O
start	O
from	O
scratch	O
and	O
create	O
an	O
OS	O
that	O
would	O
not	O
run	O
the	O
vast	O
majority	O
of	O
the	O
old	O
programs	O
,	O
or	O
to	O
come	O
up	O
with	O
a	O
version	O
of	O
DOS	B-Device
that	O
was	O
slow	O
and	O
ugly	O
(	O
i.e.	O
,	O
ugly	O
from	O
an	O
internal	O
technical	O
viewpoint	O
)	O
but	O
would	O
still	O
run	O
a	O
majority	O
of	O
the	O
old	O
programs	O
.	O
</s>
<s>
Protected	B-Application
mode	I-Application
also	O
did	O
not	O
provide	O
a	O
significant	O
enough	O
performance	O
advantage	O
over	O
the	O
8086-compatible	O
real	B-Application
mode	I-Application
to	O
justify	O
supporting	O
its	O
capabilities	O
;	O
actually	O
,	O
except	O
for	O
task	O
switches	O
when	O
multitasking	B-Operating_System
,	O
it	O
actually	O
yielded	O
only	O
a	O
performance	O
disadvantage	O
,	O
by	O
slowing	O
down	O
many	O
instructions	O
through	O
a	O
litany	O
of	O
added	O
privilege	O
checks	O
.	O
</s>
<s>
In	O
protected	B-Application
mode	I-Application
,	O
registers	O
were	O
still	O
16-bit	B-Device
,	O
and	O
the	O
programmer	O
was	O
still	O
forced	O
to	O
use	O
a	O
memory	O
map	O
composed	O
of	O
64kB	O
segments	O
,	O
just	O
like	O
in	O
real	B-Application
mode	I-Application
.	O
</s>
<s>
In	O
January	O
1985	O
,	O
Digital	O
Research	O
previewed	O
the	O
Concurrent	B-Operating_System
DOS	I-Operating_System
286	I-Operating_System
1.0	O
operating	O
system	O
developed	O
in	O
cooperation	O
with	O
Intel	O
.	O
</s>
<s>
The	O
product	O
would	O
function	O
strictly	O
as	O
an	O
80286	B-General_Concept
native-mode	O
(	O
i.e.	O
</s>
<s>
protected-mode	B-Application
)	O
operating	O
system	O
,	O
allowing	O
users	O
to	O
take	O
full	O
advantage	O
of	O
the	O
protected	B-Application
mode	I-Application
to	O
perform	O
multi-user	B-Operating_System
,	O
multitasking	B-Operating_System
operations	O
while	O
running	O
8086	B-General_Concept
emulation	B-Application
.	O
</s>
<s>
This	O
worked	O
on	O
the	O
B-1	O
prototype	O
step	O
of	O
the	O
chip	O
,	O
but	O
Digital	O
Research	O
discovered	O
problems	O
with	O
the	O
emulation	B-Application
on	O
the	O
production	O
level	O
C-1	O
step	O
in	O
May	O
,	O
which	O
would	O
not	O
allow	O
Concurrent	B-Operating_System
DOS	I-Operating_System
286	I-Operating_System
to	O
run	O
8086	B-General_Concept
software	O
in	O
protected	B-Application
mode	I-Application
.	O
</s>
<s>
The	O
release	O
of	O
Concurrent	B-Operating_System
DOS	I-Operating_System
286	I-Operating_System
was	O
delayed	O
until	O
Intel	O
would	O
develop	O
a	O
new	O
version	O
of	O
the	O
chip	O
.	O
</s>
<s>
In	O
August	O
,	O
after	O
extensive	O
testing	O
on	O
E-1	O
step	O
samples	O
of	O
the	O
80286	B-General_Concept
,	O
Digital	O
Research	O
acknowledged	O
that	O
Intel	O
corrected	O
all	O
documented	O
286	B-General_Concept
errata	O
,	O
but	O
said	O
that	O
there	O
were	O
still	O
undocumented	O
chip	O
performance	O
problems	O
with	O
the	O
prerelease	O
version	O
of	O
Concurrent	B-Operating_System
DOS	I-Operating_System
286	I-Operating_System
running	O
on	O
the	O
E-1	O
step	O
.	O
</s>
<s>
Intel	O
said	O
that	O
the	O
approach	O
Digital	O
Research	O
wished	O
to	O
take	O
in	O
emulating	B-Application
8086	B-General_Concept
software	O
in	O
protected	B-Application
mode	I-Application
differed	O
from	O
the	O
original	O
specifications	O
.	O
</s>
<s>
Nevertheless	O
,	O
in	O
the	O
E-2	O
step	O
,	O
they	O
implemented	O
minor	O
changes	O
in	O
the	O
microcode	B-Device
that	O
would	O
allow	O
Digital	O
Research	O
to	O
run	O
emulation	B-Application
mode	O
much	O
faster	O
.	O
</s>
<s>
Named	O
IBM	B-Language
4680	I-Language
OS	I-Language
,	O
IBM	O
originally	O
chose	O
DR	O
Concurrent	B-Operating_System
DOS	I-Operating_System
286	I-Operating_System
as	O
the	O
basis	O
of	O
their	O
IBM	O
4680	O
computer	O
for	O
IBM	O
Plant	O
System	O
products	O
and	O
point-of-sale	O
terminals	O
in	O
1986	O
.	O
</s>
<s>
Digital	O
Research	O
's	O
FlexOS	B-Operating_System
286	I-Operating_System
version	O
1.3	O
,	O
a	O
derivation	O
of	O
Concurrent	B-Operating_System
DOS	I-Operating_System
286	I-Operating_System
,	O
was	O
developed	O
in	O
1986	O
,	O
introduced	O
in	O
January	O
1987	O
,	O
and	O
later	O
adopted	O
by	O
IBM	O
for	O
their	O
IBM	B-Language
4690	I-Language
OS	I-Language
,	O
but	O
the	O
same	O
limitations	O
affected	O
it	O
.	O
</s>
<s>
The	O
problems	O
led	O
to	O
Bill	O
Gates	O
famously	O
referring	O
to	O
the	O
80286	B-General_Concept
as	O
a	O
"	O
brain-dead	O
chip	O
"	O
,	O
since	O
it	O
was	O
clear	O
that	O
the	O
new	O
Microsoft	B-Application
Windows	I-Application
environment	O
would	O
not	O
be	O
able	O
to	O
run	O
multiple	O
MS-DOS	B-Application
applications	O
with	O
the	O
286	B-General_Concept
.	O
</s>
<s>
It	O
was	O
arguably	O
responsible	O
for	O
the	O
split	O
between	O
Microsoft	O
and	O
IBM	O
,	O
since	O
IBM	O
insisted	O
that	O
OS/2	B-Application
,	O
originally	O
a	O
joint	O
venture	O
between	O
IBM	O
and	O
Microsoft	O
,	O
would	O
run	O
on	O
a	O
286	B-General_Concept
(	O
and	O
in	O
text	O
mode	O
)	O
.	O
</s>
<s>
Other	O
operating	O
systems	O
that	O
used	O
the	O
protected	B-Application
mode	I-Application
of	O
the	O
286	B-General_Concept
were	O
Microsoft	B-Application
Xenix	I-Application
(	O
around	O
1984	O
)	O
,	O
Coherent	B-Operating_System
,	O
and	O
Minix	B-Operating_System
.	O
</s>
<s>
These	O
were	O
less	O
hindered	O
by	O
the	O
limitations	O
of	O
the	O
80286	B-General_Concept
protected	B-Application
mode	I-Application
because	O
they	O
did	O
not	O
aim	O
to	O
run	O
MS-DOS	B-Application
applications	O
or	O
other	O
real-mode	B-Application
programs	O
.	O
</s>
<s>
In	O
its	O
successor	O
80386	B-General_Concept
chip	O
,	O
Intel	O
enhanced	O
the	O
protected	B-Application
mode	I-Application
to	O
address	B-Architecture
more	O
memory	O
and	O
also	O
added	O
the	O
separate	O
virtual	B-Application
8086	I-Application
mode	I-Application
,	O
a	O
mode	O
within	O
protected	B-Application
mode	I-Application
with	O
much	O
better	O
MS-DOS	B-Application
compatibility	O
,	O
in	O
order	O
to	O
satisfy	O
the	O
diverging	O
needs	O
of	O
the	O
market	O
.	O
</s>
<s>
This	O
list	O
of	O
bus	O
interface	O
components	O
that	O
connects	O
to	O
Intel	B-General_Concept
80286	I-General_Concept
microprocessor	B-Architecture
.	O
</s>
<s>
82230/82231	O
High	O
Integration	O
AT-Compatible	O
Chip	O
Set	O
-	O
The	O
82230	O
covers	O
this	O
combination	O
of	O
chips	O
:	O
82C284	O
clock	O
,	O
82288	B-Device
bus	O
controller	O
,	O
and	O
dual	O
8259A	O
interrupt	O
controllers	O
among	O
with	O
other	O
components	O
.	O
</s>
<s>
The	O
Intel	O
branded	O
chipset	O
was	O
available	O
in	O
20-pin	O
PLCC	B-Algorithm
in	O
sampling	O
at	O
first	O
quarter	O
1986	O
.	O
</s>
