<s>
In	O
IBM	O
PC	O
compatible	O
computing	O
,	O
DOS	B-General_Concept
memory	I-General_Concept
management	I-General_Concept
refers	O
to	O
software	O
and	O
techniques	O
employed	O
to	O
give	O
applications	O
access	O
to	O
more	O
than	O
640	O
kibibytes	O
(	O
640*1024	O
bytes	B-Application
)	O
(	O
KiB	O
)	O
of	O
"	O
conventional	B-Device
memory	I-Device
"	O
.	O
</s>
<s>
The	O
640	O
KiB	O
limit	O
was	O
specific	O
to	O
the	O
IBM	O
PC	O
and	O
close	O
compatibles	O
;	O
other	O
machines	O
running	O
MS-DOS	B-Application
had	O
different	O
limits	O
,	O
for	O
example	O
the	O
Apricot	O
PC	O
could	O
have	O
up	O
to	O
768	O
KiB	O
and	O
the	O
Sirius	O
Victor	O
9000	O
,	O
896	O
KiB	O
.	O
</s>
<s>
Memory	O
management	O
on	O
the	O
IBM	O
family	O
was	O
made	O
complex	O
by	O
the	O
need	O
to	O
maintain	O
backward	O
compatibility	O
to	O
the	O
original	O
PC	O
design	O
and	O
real-mode	B-Application
DOS	B-Device
,	O
while	O
allowing	O
computer	O
users	O
to	O
take	O
advantage	O
of	O
large	O
amounts	O
of	O
low-cost	O
memory	O
and	O
new	O
generations	O
of	O
processors	O
.	O
</s>
<s>
Since	O
DOS	B-Device
has	O
given	O
way	O
to	O
Microsoft	B-Application
Windows	I-Application
and	O
other	O
32-bit	O
operating	B-General_Concept
systems	I-General_Concept
not	O
restricted	O
by	O
the	O
original	O
arbitrary	O
640	O
KiB	O
limit	O
of	O
the	O
IBM	O
PC	O
,	O
managing	O
the	O
memory	O
of	O
a	O
personal	O
computer	O
no	O
longer	O
requires	O
the	O
user	O
to	O
manually	O
manipulate	O
internal	O
settings	O
and	O
parameters	O
of	O
the	O
system	O
.	O
</s>
<s>
The	O
640	O
KiB	O
limit	O
imposed	O
great	O
complexity	O
on	O
hardware	O
and	O
software	O
intended	O
to	O
circumvent	O
it	O
;	O
the	O
physical	O
memory	O
in	O
a	O
machine	O
could	O
be	O
organised	O
as	O
a	O
combination	O
of	O
base	O
or	O
conventional	B-Device
memory	I-Device
(	O
including	O
lower	O
memory	O
)	O
,	O
upper	B-Device
memory	I-Device
,	O
high	O
memory	O
(	O
not	O
the	O
same	O
as	O
upper	B-Device
memory	I-Device
)	O
,	O
extended	B-Device
memory	I-Device
,	O
and	O
expanded	O
memory	O
,	O
all	O
handled	O
in	O
different	O
ways	O
.	O
</s>
<s>
The	O
Intel	B-Device
8088	I-Device
processor	O
used	O
in	O
the	O
original	O
IBM	O
PC	O
had	O
20	O
address	O
lines	O
and	O
so	O
could	O
directly	O
address	O
1	O
MiB	O
(	O
220	O
bytes	B-Application
)	O
of	O
memory	O
.	O
</s>
<s>
Starting	O
at	O
the	O
lowest	O
end	O
of	O
the	O
address	O
space	O
,	O
the	O
PC	O
had	O
read/write	O
random	B-Architecture
access	I-Architecture
memory	I-Architecture
(	O
RAM	B-Architecture
)	O
installed	O
,	O
which	O
was	O
used	O
by	O
DOS	B-Device
and	O
application	O
programs	O
.	O
</s>
<s>
Additional	O
memory	O
could	O
be	O
added	O
with	O
cards	O
plugged	O
into	O
the	O
expansion	B-Device
slots	I-Device
;	O
each	O
card	O
contained	O
straps	O
or	O
switches	O
to	O
control	O
what	O
part	O
of	O
the	O
address	O
space	O
accesses	O
memory	O
and	O
devices	O
on	O
that	O
card	O
.	O
</s>
<s>
On	O
the	O
IBM	O
PC	O
,	O
all	O
the	O
address	O
space	O
up	O
to	O
640	O
KiB	O
was	O
available	O
for	O
RAM	B-Architecture
.	O
</s>
<s>
This	O
part	O
of	O
the	O
address	O
space	O
is	O
called	O
"	O
conventional	B-Device
memory	I-Device
"	O
since	O
it	O
is	O
accessible	O
to	O
all	O
versions	O
of	O
DOS	B-Device
automatically	O
on	O
startup	O
.	O
</s>
<s>
Segment	O
0	O
,	O
the	O
first	O
64KiB	O
of	O
conventional	B-Device
memory	I-Device
,	O
is	O
also	O
called	O
low	B-Device
memory	I-Device
area	O
.	O
</s>
<s>
If	O
there	O
was	O
an	O
unallocated	O
gap	O
between	O
motherboard	O
memory	O
and	O
the	O
expansion	O
memory	O
,	O
the	O
memory	O
would	O
not	O
be	O
automatically	O
detected	O
as	O
usable	O
by	O
DOS	B-Device
.	O
</s>
<s>
The	O
upper	B-Device
memory	I-Device
area	I-Device
(	O
UMA	B-Device
)	O
refers	O
to	O
the	O
address	O
space	O
between	O
640	O
KiB	O
and	O
1024	O
KiB	O
(	O
0xA0000	O
–	O
0xFFFFF	O
)	O
.	O
</s>
<s>
The	O
128	O
KiB	O
region	O
between	O
0xA0000	O
and	O
0xBFFFF	O
was	O
reserved	O
for	O
VGA	B-Protocol
screen	O
memory	O
and	O
legacy	O
SMM	O
.	O
</s>
<s>
The	O
128	O
KiB	O
region	O
between	O
0xC0000	O
and	O
0xDFFFF	O
was	O
reserved	O
for	O
device	O
Option	O
ROMs	O
,	O
including	O
Video	B-Device
BIOS	I-Device
.	O
</s>
<s>
The	O
64	O
KiB	O
of	O
the	O
address	O
space	O
from	O
0xE0000	O
to	O
0xEFFFF	O
was	O
reserved	O
for	O
the	O
BIOS	B-Operating_System
or	O
Option	O
ROMs	O
.	O
</s>
<s>
The	O
IBM	O
PC	O
reserved	O
the	O
uppermost	O
64	O
KiB	O
of	O
the	O
address	O
space	O
from	O
0xF0000	O
to	O
0xFFFFF	O
for	O
the	O
BIOS	B-Operating_System
and	O
Cassette	O
BASIC	O
read-only	O
memory	O
(	O
ROM	O
)	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
monochrome	B-Device
video	I-Device
adapter	I-Device
memory	O
area	O
ran	O
from	O
704	O
to	O
736	O
KiB	O
(	O
0xB0000	O
–	O
0xB7FFF	O
)	O
.	O
</s>
<s>
If	O
only	O
a	O
monochrome	B-Device
display	I-Device
adapter	I-Device
was	O
used	O
,	O
the	O
address	O
space	O
between	O
0xA0000	O
and	O
0xAFFFF	O
could	O
be	O
used	O
for	O
RAM	B-Architecture
,	O
which	O
would	O
be	O
contiguous	O
with	O
the	O
conventional	B-Device
memory	I-Device
.	O
</s>
<s>
The	O
system	B-Operating_System
BIOS	I-Operating_System
ROMs	O
must	O
be	O
at	O
the	O
upper	O
end	O
of	O
the	O
address	O
space	O
because	O
the	O
CPU	O
starting	O
address	O
is	O
fixed	O
by	O
the	O
design	O
of	O
the	O
processor	O
.	O
</s>
<s>
The	O
starting	O
address	O
is	O
loaded	O
into	O
the	O
program	B-General_Concept
counter	I-General_Concept
of	O
the	O
CPU	O
after	O
a	O
hardware	O
reset	O
and	O
must	O
have	O
a	O
defined	O
value	O
that	O
endures	O
after	O
power	O
is	O
interrupted	O
to	O
the	O
system	O
.	O
</s>
<s>
On	O
reset	O
or	O
power	O
up	O
,	O
the	O
CPU	O
loads	O
the	O
address	O
from	O
the	O
system	O
ROM	O
and	O
then	O
jumps	O
to	O
a	O
defined	O
ROM	O
location	O
to	O
begin	O
executing	O
the	O
system	O
power-on	B-Device
self-test	I-Device
,	O
and	O
eventually	O
load	O
an	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Since	O
an	O
expansion	B-Device
card	I-Device
such	O
as	O
a	O
video	O
adapter	O
,	O
hard	B-General_Concept
drive	I-General_Concept
controller	I-General_Concept
,	O
or	O
network	O
adapter	O
could	O
use	O
allocations	O
of	O
memory	O
in	O
many	O
of	O
the	O
upper	B-Device
memory	I-Device
areas	I-Device
,	O
configuration	O
of	O
some	O
combinations	O
of	O
cards	O
required	O
careful	O
reading	O
of	O
documentation	O
,	O
or	O
experimentation	O
,	O
to	O
find	O
card	O
settings	O
and	O
memory	B-Architecture
mappings	I-Architecture
that	O
worked	O
.	O
</s>
<s>
Not	O
all	O
addresses	O
in	O
the	O
upper	B-Device
memory	I-Device
area	I-Device
were	O
used	O
in	O
a	O
typical	O
system	O
;	O
unused	O
physical	O
addresses	O
would	O
return	O
undefined	O
and	O
system-dependent	O
data	O
if	O
accessed	O
by	O
the	O
processor	O
.	O
</s>
<s>
As	O
memory	O
prices	O
declined	O
,	O
application	O
programs	O
such	O
as	O
spreadsheets	B-Application
and	O
computer-aided	B-Application
drafting	I-Application
were	O
changed	O
to	O
take	O
advantage	O
of	O
more	O
and	O
more	O
physical	O
memory	O
in	O
the	O
system	O
.	O
</s>
<s>
Virtual	B-Architecture
memory	I-Architecture
in	O
the	O
8088	B-Device
and	O
8086	B-General_Concept
was	O
not	O
supported	O
by	O
the	O
processor	O
hardware	O
,	O
and	O
disk	O
technology	O
of	O
the	O
time	O
would	O
make	O
it	O
too	O
slow	O
and	O
cumbersome	O
to	O
be	O
practical	O
.	O
</s>
<s>
Expanded	O
memory	O
was	O
a	O
system	O
that	O
allowed	O
application	O
programs	O
to	O
access	O
more	O
RAM	B-Architecture
than	O
directly	O
visible	O
to	O
the	O
processor	O
's	O
address	O
space	O
.	O
</s>
<s>
The	O
process	O
was	O
a	O
form	O
of	O
bank	B-General_Concept
switching	I-General_Concept
.	O
</s>
<s>
When	O
extra	O
RAM	B-Architecture
was	O
needed	O
,	O
driver	B-Application
software	I-Application
would	O
temporarily	O
make	O
a	O
piece	O
of	O
expanded	O
memory	O
accessible	O
to	O
the	O
processor	O
;	O
when	O
the	O
data	O
in	O
that	O
piece	O
of	O
memory	O
was	O
updated	O
,	O
another	O
part	O
could	O
be	O
swapped	O
into	O
the	O
processor	O
's	O
address	O
space	O
.	O
</s>
<s>
For	O
the	O
IBM	O
PC	O
and	O
IBM	B-Device
PC/XT	I-Device
,	O
with	O
only	O
20	O
address	O
lines	O
,	O
special-purpose	O
expanded	O
memory	O
cards	O
were	O
made	O
containing	O
perhaps	O
a	O
megabyte	O
,	O
or	O
more	O
,	O
of	O
expanded	O
memory	O
,	O
with	O
logic	O
on	O
the	O
board	O
to	O
make	O
that	O
memory	O
accessible	O
to	O
the	O
processor	O
in	O
defined	O
parts	O
of	O
the	O
8088	B-Device
address	O
space	O
.	O
</s>
<s>
The	O
application	O
had	O
to	O
keep	O
track	O
of	O
which	O
bank	O
of	O
expanded	O
memory	O
contained	O
a	O
particular	O
piece	O
of	O
data	O
,	O
and	O
when	O
access	O
to	O
that	O
data	O
was	O
required	O
,	O
the	O
application	O
had	O
to	O
request	O
(	O
through	O
a	O
driver	B-Application
program	O
)	O
the	O
expanded	O
memory	O
board	O
to	O
map	O
that	O
part	O
of	O
memory	O
into	O
the	O
processor	O
's	O
address	O
space	O
.	O
</s>
<s>
Although	O
applications	O
could	O
use	O
expanded	O
memory	O
with	O
relative	O
freedom	O
,	O
many	O
other	O
software	O
components	O
such	O
as	O
drivers	O
and	O
terminate-and-stay-resident	O
programs	O
(	O
TSRs	O
)	O
were	O
still	O
normally	O
constrained	O
to	O
reside	O
within	O
the	O
640K	B-Device
"	O
conventional	B-Device
memory	I-Device
"	O
area	O
,	O
which	O
soon	O
became	O
a	O
critically	O
scarce	O
resource	O
.	O
</s>
<s>
When	O
the	O
IBM	B-Operating_System
PC/AT	I-Operating_System
was	O
introduced	O
,	O
the	O
segmented	B-Device
memory	I-Device
architecture	O
of	O
the	O
Intel	O
family	O
processors	O
had	O
the	O
byproduct	O
of	O
allowing	O
slightly	O
more	O
than	O
1	O
MiB	O
of	O
memory	O
to	O
be	O
addressed	O
in	O
the	O
"	O
real	O
"	O
mode	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
some	O
DOS	B-Device
programs	O
would	O
no	O
longer	O
work	O
.	O
</s>
<s>
To	O
maintain	O
compatibility	O
with	O
the	O
PC	O
and	O
XT	O
behavior	O
,	O
the	O
AT	O
included	O
an	O
A20	O
line	O
gate	O
(	O
Gate	O
A20	O
)	O
that	O
made	O
memory	O
addresses	O
on	O
the	O
AT	O
wrap	O
around	O
to	O
low	B-Device
memory	I-Device
as	O
they	O
would	O
have	O
on	O
an	O
8088	B-Device
processor	O
.	O
</s>
<s>
This	O
gate	O
could	O
be	O
controlled	O
,	O
initially	O
through	O
the	O
keyboard	B-Device
controller	I-Device
,	O
to	O
allow	O
running	O
programs	O
which	O
were	O
designed	O
for	O
this	O
to	O
access	O
an	O
additional	O
65,520	O
bytes	B-Application
(	O
64	O
KiB	O
of	O
memory	O
in	O
real	B-Application
mode	I-Application
.	O
</s>
<s>
At	O
boot	B-Operating_System
time	I-Operating_System
,	O
the	O
BIOS	B-Operating_System
first	O
enables	O
A20	O
when	O
counting	O
and	O
testing	O
all	O
of	O
the	O
system	O
's	O
memory	O
,	O
and	O
disables	O
it	O
before	O
transferring	O
control	O
to	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Enabling	O
the	O
A20	O
line	O
is	O
one	O
of	O
the	O
first	O
steps	O
a	O
protected	B-Application
mode	I-Application
x86	B-Operating_System
operating	B-General_Concept
system	I-General_Concept
does	O
in	O
the	O
bootup	B-Operating_System
process	O
,	O
often	O
before	O
control	O
has	O
been	O
passed	O
onto	O
the	O
kernel	O
from	O
the	O
bootstrap	O
(	O
in	O
the	O
case	O
of	O
Linux	O
,	O
for	O
example	O
)	O
.	O
</s>
<s>
The	O
high	O
memory	O
area	O
(	O
HMA	O
)	O
is	O
the	O
RAM	B-Architecture
area	O
consisting	O
of	O
the	O
first	O
64	O
KiB	O
,	O
minus	O
16	O
bytes	B-Application
,	O
of	O
the	O
extended	B-Device
memory	I-Device
on	O
an	O
IBM	B-Operating_System
PC/AT	I-Operating_System
or	O
compatible	O
microcomputer	O
.	O
</s>
<s>
Originally	O
,	O
the	O
logic	O
gate	O
was	O
a	O
gate	O
connected	O
to	O
the	O
Intel	B-Device
8042	I-Device
keyboard	B-Device
controller	I-Device
.	O
</s>
<s>
There	O
was	O
at	O
first	O
a	O
variety	O
of	O
methods	O
,	O
but	O
eventually	O
the	O
industry	O
settled	O
on	O
the	O
PS/2	O
method	O
of	O
using	O
a	O
bit	O
in	O
port	B-General_Concept
92h	O
to	O
control	O
the	O
A20	O
line	O
.	O
</s>
<s>
Real	B-Application
mode	I-Application
software	O
only	O
cared	O
about	O
the	O
area	O
slightly	O
above	O
1	O
MiB	O
,	O
so	O
Gate	O
A20	O
was	O
enough	O
.	O
</s>
<s>
Virtual	B-Application
8086	I-Application
mode	I-Application
,	O
introduced	O
with	O
the	O
Intel	B-General_Concept
80386	I-General_Concept
,	O
allows	O
the	O
A20	O
wrap-around	O
to	O
be	O
simulated	O
by	O
using	O
the	O
virtual	B-Architecture
memory	I-Architecture
facilities	O
of	O
the	O
processor	O
:	O
physical	O
memory	O
may	O
be	O
mapped	O
to	O
multiple	O
virtual	O
addresses	O
,	O
thus	O
allowing	O
that	O
the	O
memory	O
mapped	O
at	O
the	O
first	O
megabyte	O
of	O
virtual	B-Architecture
memory	I-Architecture
may	O
be	O
mapped	O
again	O
in	O
the	O
second	O
megabyte	O
of	O
virtual	B-Architecture
memory	I-Architecture
.	O
</s>
<s>
The	O
operating	B-General_Concept
system	I-General_Concept
may	O
intercept	O
changes	O
to	O
Gate	O
A20	O
and	O
make	O
corresponding	O
changes	O
to	O
the	O
virtual	B-Architecture
memory	I-Architecture
address	O
space	O
,	O
which	O
also	O
makes	O
irrelevant	O
the	O
efficiency	O
of	O
Gate-A20	O
toggling	O
.	O
</s>
<s>
The	O
first	O
user	O
of	O
the	O
HMA	O
among	O
Microsoft	O
products	O
was	O
Windows	B-Application
2.0	I-Application
in	O
1987	O
,	O
which	O
introduced	O
the	O
HIMEM.SYS	O
device	B-Application
driver	I-Application
.	O
</s>
<s>
Starting	O
with	O
versions	O
5.0	O
of	O
DR-DOS	B-Application
(	O
1990	O
)	O
and	O
of	O
MS-DOS	B-Application
(	O
1991	O
)	O
,	O
parts	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
could	O
be	O
loaded	O
into	O
HMA	O
as	O
well	O
,	O
freeing	O
up	O
to	O
46	O
KiB	O
of	O
conventional	B-Device
memory	I-Device
.	O
</s>
<s>
Other	O
components	O
,	O
such	O
as	O
device	B-Application
drivers	I-Application
and	O
TSRs	O
,	O
could	O
be	O
loaded	O
into	O
the	O
upper	B-Device
memory	I-Device
area	I-Device
(	O
UMA	B-Device
)	O
.	O
</s>
<s>
Extended	B-Device
memory	I-Device
managers	O
usually	O
provide	O
this	O
functionality	O
.	O
</s>
<s>
In	O
DOS	B-Device
,	O
high	O
memory	O
area	O
managers	O
,	O
such	O
as	O
HIMEM.SYS	O
had	O
the	O
extra	O
task	O
of	O
managing	O
A20	O
and	O
provided	O
an	O
API	B-General_Concept
for	O
opening/closing	O
A20	O
.	O
</s>
<s>
DOS	B-Device
itself	O
could	O
utilize	O
the	O
area	O
for	O
some	O
of	O
its	O
storage	O
needs	O
,	O
thereby	O
freeing	O
up	O
more	O
conventional	B-Device
memory	I-Device
for	O
programs	O
.	O
</s>
<s>
This	O
functionality	O
was	O
enabled	O
by	O
the	O
"	O
DOS	B-Device
=	O
HIGH	O
"	O
directive	O
in	O
the	O
CONFIG.SYS	B-Device
configuration	O
file	O
.	O
</s>
<s>
The	O
Intel	B-General_Concept
80486	I-General_Concept
and	O
Pentium	B-General_Concept
added	O
a	O
special	O
pin	O
named	O
A20M#	O
,	O
which	O
when	O
asserted	O
low	O
forces	O
bit	O
20	O
of	O
the	O
physical	O
address	O
to	O
be	O
zero	O
for	O
all	O
on-chip	O
cache	O
or	O
external	O
memory	O
accesses	O
.	O
</s>
<s>
This	O
was	O
necessary	O
since	O
the	O
80486	B-General_Concept
introduced	O
an	O
on-chip	O
cache	O
,	O
and	O
therefore	O
masking	O
this	O
bit	O
in	O
external	O
logic	O
was	O
no	O
longer	O
possible	O
.	O
</s>
<s>
Software	O
still	O
needs	O
to	O
manipulate	O
the	O
gate	O
and	O
must	O
still	O
deal	O
with	O
external	O
peripherals	O
(	O
the	O
chipset	B-Device
)	O
for	O
that	O
.	O
</s>
<s>
Intel	O
processors	O
from	O
the	O
386	B-General_Concept
onward	O
allowed	O
a	O
virtual	B-Application
8086	I-Application
mode	I-Application
,	O
which	O
simplified	O
the	O
hardware	O
required	O
to	O
implement	O
expanded	O
memory	O
for	O
DOS	B-Device
applications	O
.	O
</s>
<s>
Expanded	O
memory	O
managers	O
such	O
as	O
Quarterdeck	O
's	O
QEMM	B-Device
product	O
and	O
Microsoft	O
's	O
EMM386	B-Device
supported	O
the	O
expanded	O
memory	O
standard	O
without	O
requirement	O
for	O
special	O
memory	O
boards	O
.	O
</s>
<s>
On	O
386	B-General_Concept
and	O
subsequent	O
processors	O
,	O
memory	O
managers	O
like	O
QEMM	B-Device
might	O
move	O
the	O
bulk	O
of	O
the	O
code	O
for	O
a	O
driver	B-Application
or	O
TSR	O
into	O
extended	B-Device
memory	I-Device
and	O
replace	O
it	O
with	O
a	O
small	O
fingerhold	O
that	O
was	O
capable	O
of	O
accessing	O
the	O
extended-memory-resident	O
code	O
.	O
</s>
<s>
They	O
might	O
analyze	O
memory	O
usage	O
to	O
detect	O
drivers	O
that	O
required	O
more	O
RAM	B-Architecture
during	O
startup	O
than	O
they	O
did	O
subsequently	O
,	O
and	O
recover	O
and	O
reuse	O
the	O
memory	O
that	O
was	O
no	O
longer	O
needed	O
after	O
startup	O
.	O
</s>
<s>
They	O
might	O
even	O
remap	O
areas	O
of	O
memory	O
normally	O
used	O
for	O
memory-mapped	B-Architecture
I/O	I-Architecture
.	O
</s>
<s>
But	O
conventional	B-Device
memory	I-Device
was	O
so	O
valuable	O
that	O
PC	O
owners	O
felt	O
that	O
such	O
time	O
was	O
well-spent	O
if	O
the	O
result	O
was	O
to	O
free	O
up	O
30	O
KiB	O
or	O
40	O
KiB	O
of	O
conventional	B-Device
memory	I-Device
space	O
.	O
</s>
<s>
In	O
the	O
context	O
of	O
IBM	O
PC	O
compatible	O
computers	O
,	O
extended	B-Device
memory	I-Device
refers	O
to	O
memory	O
in	O
the	O
address	O
space	O
of	O
the	O
80286	O
and	O
subsequent	O
processors	O
,	O
beyond	O
the	O
1	O
megabyte	O
limit	O
imposed	O
by	O
the	O
20	O
address	O
lines	O
of	O
the	O
8088	B-Device
and	O
8086	B-General_Concept
.	O
</s>
<s>
Such	O
memory	O
is	O
not	O
directly	O
available	O
to	O
DOS	B-Device
applications	O
running	O
in	O
the	O
so-called	O
"	O
real	B-Application
mode	I-Application
"	O
of	O
the	O
80286	O
and	O
subsequent	O
processors	O
.	O
</s>
