<s>
IBM	B-Application
i	I-Application
(	O
the	O
i	O
standing	O
for	O
integrated	O
)	O
is	O
an	O
operating	B-General_Concept
system	I-General_Concept
developed	O
by	O
IBM	O
for	O
IBM	B-Device
Power	I-Device
Systems	I-Device
.	O
</s>
<s>
It	O
was	O
originally	O
released	O
in	O
1988	O
as	O
OS/400	B-Application
,	O
as	O
the	O
sole	O
operating	B-General_Concept
system	I-General_Concept
of	O
the	O
IBM	B-Device
AS/400	I-Device
line	O
of	O
systems	O
.	O
</s>
<s>
It	O
was	O
renamed	O
to	O
i5/OS	B-Application
in	O
2004	O
,	O
before	O
being	O
renamed	O
a	O
second	O
time	O
to	O
IBM	B-Application
i	I-Application
in	O
2008	O
.	O
</s>
<s>
It	O
is	O
an	O
evolution	O
of	O
the	O
System/38	B-Device
CPF	B-Operating_System
operating	B-General_Concept
system	I-General_Concept
,	O
with	O
compatibility	B-General_Concept
layers	I-General_Concept
for	O
System/36	B-Device
SSP	B-Operating_System
and	O
AIX	B-Application
applications	O
.	O
</s>
<s>
It	O
inherits	O
a	O
number	O
of	O
distinctive	O
features	O
from	O
the	O
System/38	B-Device
platform	O
,	O
including	O
the	O
Machine	O
Interface	O
,	O
the	O
implementation	O
of	O
object-based	O
addressing	O
on	O
top	O
of	O
a	O
single-level	B-Device
store	I-Device
,	O
and	O
the	O
tight	O
integration	O
of	O
a	O
relational	B-Application
database	I-Application
into	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
OS/400	B-Application
was	O
developed	O
alongside	O
the	O
AS/400	B-Device
hardware	O
platform	O
beginning	O
in	O
December	O
1985	O
.	O
</s>
<s>
Development	O
began	O
in	O
the	O
aftermath	O
of	O
the	O
failure	O
of	O
the	O
Fort	O
Knox	O
project	O
,	O
which	O
left	O
IBM	O
without	O
a	O
competitive	O
midrange	B-Device
system	I-Device
.	O
</s>
<s>
During	O
the	O
Fort	O
Knox	O
project	O
,	O
a	O
skunkworks	O
project	O
was	O
started	O
at	O
Rochester	O
by	O
engineers	O
,	O
who	O
succeeded	O
in	O
developing	O
code	O
which	O
allowed	O
System/36	B-Device
applications	O
to	O
run	O
on	O
top	O
of	O
the	O
System/38	B-Device
,	O
and	O
when	O
Fort	O
Knox	O
was	O
cancelled	O
,	O
this	O
project	O
evolved	O
into	O
an	O
official	O
project	O
to	O
replace	O
both	O
the	O
System/36	B-Device
and	O
System/38	B-Device
with	O
a	O
single	O
new	O
hardware	O
and	O
software	O
platform	O
.	O
</s>
<s>
The	O
operating	B-General_Concept
system	I-General_Concept
for	O
Silverlake	O
was	O
codenamed	O
XPF	O
(	O
Extended	O
CPF	B-Operating_System
)	O
,	O
and	O
had	O
originally	O
begun	O
as	O
a	O
port	O
of	O
CPF	B-Operating_System
to	O
the	O
Fort	O
Knox	O
hardware	O
.	O
</s>
<s>
In	O
addition	O
to	O
adding	O
support	O
for	O
System/36	B-Device
applications	O
,	O
some	O
of	O
the	O
user	O
interface	O
and	O
ease-of-use	O
features	O
from	O
the	O
System/36	B-Device
were	O
carried	O
over	O
to	O
the	O
new	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
By	O
that	O
point	O
,	O
it	O
had	O
been	O
renamed	O
to	O
the	O
Application	B-Device
System/400	I-Device
,	O
and	O
the	O
operating	B-General_Concept
system	I-General_Concept
had	O
been	O
named	O
Operating	O
System/400	O
.	O
</s>
<s>
Early	O
versions	O
of	O
OS/400	B-Application
inherited	O
the	O
Horizontal	O
and	O
Vertical	O
Microcode	O
layers	O
of	O
the	O
System/38	B-Device
,	O
although	O
they	O
were	O
renamed	O
to	O
the	O
Horizontal	O
Licensed	O
Internal	O
Code	O
(	O
HLIC	O
)	O
and	O
Vertical	O
Licensed	O
Internal	O
Code	O
(	O
VLIC	O
)	O
respectively	O
.	O
</s>
<s>
The	O
port	O
to	O
the	O
new	O
hardware	O
led	O
to	O
the	O
IMPI	O
instruction	B-General_Concept
set	I-General_Concept
and	O
the	O
horizontal	O
microcode	O
implementing	O
it	O
being	O
replaced	O
by	O
the	O
PowerPC	O
AS	O
instruction	B-General_Concept
set	I-General_Concept
and	O
its	O
implementation	O
in	O
PowerAS	O
processors	O
.	O
</s>
<s>
This	O
required	O
the	O
VLIC	O
to	O
be	O
rewritten	O
to	O
target	O
PowerPC	O
instead	O
of	O
IMPI	O
,	O
and	O
for	O
the	O
operating	B-General_Concept
system	I-General_Concept
functionality	O
previously	O
implemented	O
in	O
the	O
HLIC	O
to	O
be	O
re-implemented	O
elsewhere	O
.	O
</s>
<s>
The	O
SLIC	O
was	O
implemented	O
in	O
an	O
object-oriented	B-Language
style	O
with	O
over	O
2	O
million	O
lines	O
of	O
C++	B-Language
code	I-Language
,	O
replacing	O
some	O
of	O
the	O
HLIC	O
code	O
,	O
and	O
most	O
of	O
the	O
VLIC	O
code	O
.	O
</s>
<s>
Owing	O
to	O
the	O
amount	O
of	O
work	O
needed	O
to	O
implement	O
the	O
SLIC	O
,	O
IBM	O
Rochester	O
hired	O
several	O
hundred	O
C++	B-Language
programmers	O
for	O
the	O
project	O
,	O
who	O
worked	O
on	O
the	O
SLIC	O
in	O
parallel	O
to	O
new	O
revisions	O
of	O
the	O
VLIC	O
for	O
the	O
CISC	O
AS/400	B-Device
systems	O
.	O
</s>
<s>
The	O
first	O
release	O
of	O
OS/400	B-Application
to	O
support	O
PowerPC-based	O
hardware	O
was	O
V3R6	O
.	O
</s>
<s>
The	O
AS/400	B-Device
product	O
line	O
was	O
rebranded	O
multiple	O
times	O
throughout	O
the	O
1990s	O
and	O
2000s	O
.	O
</s>
<s>
As	O
part	O
of	O
the	O
2004	O
rebranding	O
to	O
eServer	O
i5	O
,	O
OS/400	B-Application
was	O
renamed	O
to	O
i5/OS	B-Application
;	O
the	O
5	O
signifying	O
the	O
use	O
of	O
POWER5	B-Device
processors	O
.	O
</s>
<s>
The	O
first	O
release	O
of	O
i5/OS	B-Application
,	O
V5R3	O
,	O
was	O
described	O
by	O
IBM	O
as	O
"	O
a	O
different	O
name	O
for	O
the	O
same	O
operating	B-General_Concept
system	I-General_Concept
"	O
.	O
</s>
<s>
In	O
2006	O
,	O
IBM	O
rebranded	O
the	O
AS/400	B-Device
line	O
one	O
last	O
time	O
to	O
System	O
i	O
.	O
</s>
<s>
In	O
April	O
2008	O
,	O
IBM	O
consolidated	O
the	O
System	O
i	O
with	O
the	O
System	B-Device
p	I-Device
platform	O
to	O
create	O
IBM	B-Device
Power	I-Device
Systems	I-Device
.	O
</s>
<s>
At	O
the	O
same	O
time	O
,	O
i5/OS	B-Application
was	O
renamed	O
to	O
IBM	B-Application
i	I-Application
,	O
in	O
order	O
to	O
remove	O
the	O
association	O
with	O
POWER5	B-Device
processors	O
.	O
</s>
<s>
The	O
two	O
most	O
recent	O
versions	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
at	O
that	O
time	O
,	O
which	O
had	O
been	O
released	O
as	O
i5/OS	B-Application
V5R4	O
and	O
V6R1	O
,	O
were	O
renamed	O
to	O
IBM	B-Application
i	I-Application
5.4	O
and	O
6.1	O
.	O
</s>
<s>
Along	O
with	O
the	O
rebranding	O
to	O
IBM	B-Application
i	I-Application
,	O
IBM	O
changed	O
the	O
versioning	O
nomenclature	O
for	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Beginning	O
with	O
IBM	B-Application
i	I-Application
7.1	O
,	O
IBM	O
replaced	O
the	O
Modification	O
releases	O
with	O
Technology	O
Refreshes	O
.	O
</s>
<s>
Technology	O
Refreshes	O
are	O
delivered	O
as	O
optional	O
PTFs	B-Application
for	O
specific	O
releases	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
which	O
add	O
new	O
functionality	O
or	O
hardware	O
support	O
to	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
When	O
IBM	B-Application
i	I-Application
was	O
first	O
released	O
as	O
OS/400	B-Application
,	O
it	O
was	O
split	O
into	O
two	O
layers	O
,	O
the	O
hardware-dependent	O
System	O
Licensed	O
Internal	O
Code	O
(	O
SLIC	O
)	O
and	O
the	O
hardware-independent	O
Extended	O
Control	B-Operating_System
Program	I-Operating_System
Facility	I-Operating_System
(	O
XPF	O
)	O
.	O
</s>
<s>
These	O
are	O
divided	O
by	O
a	O
hardware	B-Operating_System
abstraction	I-Operating_System
layer	I-Operating_System
called	O
the	O
Technology	O
Independent	O
Machine	O
Interface	O
(	O
TIMI	O
)	O
.	O
</s>
<s>
Later	O
versions	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
gained	O
additional	O
layers	O
,	O
including	O
an	O
AIX	B-Application
compatibility	B-General_Concept
layer	I-General_Concept
named	O
Portable	O
Application	O
Solutions	O
Environment	O
(	O
originally	O
known	O
as	O
the	O
Private	O
Address	B-General_Concept
Space	I-General_Concept
Environment	O
)	O
,	O
and	O
the	O
Advanced	O
36	O
Machine	O
environment	O
which	O
ran	O
System/36	B-Device
SSP	B-Operating_System
applications	O
in	O
emulation	O
.	O
</s>
<s>
IBM	O
often	O
uses	O
different	O
names	O
for	O
the	O
TIMI	O
,	O
SLIC	O
and	O
XPF	O
in	O
documentation	O
and	O
marketing	O
materials	O
,	O
for	O
example	O
,	O
the	O
IBM	B-Application
i	I-Application
7.4	O
documentation	O
refers	O
to	O
them	O
as	O
the	O
IBM	B-Application
i	I-Application
Machine	O
Interface	O
,	O
IBM	B-Application
i	I-Application
Licensed	O
Internal	O
Code	O
and	O
IBM	B-Application
i	I-Application
Operating	B-General_Concept
System	I-General_Concept
respectively	O
.	O
</s>
<s>
This	O
isolation	O
is	O
more	O
thorough	O
than	O
the	O
hardware	B-Operating_System
abstractions	I-Operating_System
of	O
other	O
operating	B-General_Concept
systems	I-General_Concept
,	O
and	O
includes	O
abstracting	O
the	O
instruction	B-General_Concept
set	I-General_Concept
architecture	I-General_Concept
of	O
the	O
processor	O
,	O
the	O
size	O
of	O
the	O
address	B-General_Concept
space	I-General_Concept
and	O
the	O
specifics	O
of	O
I/O	B-General_Concept
and	O
persistence	O
.	O
</s>
<s>
Compilers	O
for	O
IBM	B-Application
i	I-Application
do	O
not	O
generate	O
native	O
machine	B-Language
code	I-Language
directly	O
,	O
instead	O
they	O
generate	O
a	O
high	O
level	O
intermediate	B-Application
representation	I-Application
defined	O
by	O
the	O
TIMI	O
.	O
</s>
<s>
When	O
a	O
program	O
is	O
run	O
,	O
the	O
operating	B-General_Concept
system	I-General_Concept
carries	O
out	O
ahead-of-time	B-Application
translation	O
of	O
the	O
TIMI	O
instructions	O
into	O
native	O
machine	B-Language
code	I-Language
for	O
the	O
processor	O
,	O
and	O
stores	O
the	O
generated	O
machine	B-Language
code	I-Language
for	O
future	O
execution	O
of	O
the	O
program	O
.	O
</s>
<s>
If	O
the	O
translation	O
process	O
changes	O
,	O
or	O
a	O
different	O
CPU	B-Language
instruction	I-Language
set	O
is	O
adopted	O
,	O
the	O
operating	B-General_Concept
system	I-General_Concept
can	O
transparently	O
regenerate	O
the	O
machine	B-Language
code	I-Language
from	O
the	O
TIMI	O
instructions	O
without	O
needing	O
to	O
recompile	O
from	O
source	O
code	O
.	O
</s>
<s>
All	O
data	O
in	O
IBM	B-Application
i	I-Application
,	O
such	O
as	O
data	O
files	O
,	O
source	O
code	O
,	O
programs	O
and	O
regions	O
of	O
allocated	O
memory	O
,	O
are	O
encapsulated	O
inside	O
objects	O
managed	O
by	O
the	O
operating	B-General_Concept
system	I-General_Concept
(	O
c.f.	O
</s>
<s>
the	O
"	O
Everything	B-Application
is	I-Application
a	I-Application
file	I-Application
"	O
model	O
in	O
Unix	B-Application
)	O
.	O
</s>
<s>
IBM	B-Application
i	I-Application
objects	O
have	O
a	O
fixed	O
type	O
,	O
which	O
defines	O
the	O
set	O
of	O
applicable	O
operations	O
which	O
may	O
be	O
carried	O
out	O
on	O
them	O
(	O
for	O
example	O
,	O
a	O
Program	O
object	O
can	O
be	O
executed	O
,	O
but	O
cannot	O
be	O
edited	O
)	O
.	O
</s>
<s>
Instead	O
,	O
the	O
operating	B-General_Concept
system	I-General_Concept
automatically	O
handles	O
the	O
process	O
of	O
retrieving	O
and	O
then	O
storing	O
the	O
changes	O
to	O
permanent	O
storage	O
.	O
</s>
<s>
The	O
hardware	O
isolation	O
provided	O
by	O
the	O
TIMI	O
allowed	O
IBM	O
to	O
replace	O
the	O
AS/400	B-Device
'	O
s	O
48-bit	O
IMPI	O
architecture	O
with	O
the	O
64-bit	O
RS64	B-Device
architecture	O
in	O
1995	O
.	O
</s>
<s>
Applications	O
compiled	O
on	O
systems	O
using	O
the	O
IMPI	O
instruction	B-General_Concept
set	I-General_Concept
could	O
run	O
on	O
top	O
of	O
the	O
newer	O
RS64	B-Device
systems	O
without	O
any	O
code	O
changes	O
,	O
recompilation	O
or	O
emulation	O
,	O
while	O
also	O
allowing	O
those	O
applications	O
to	O
avail	O
of	O
64-bit	O
addressing	O
.	O
</s>
<s>
OMI	O
instructions	O
are	O
essentially	O
the	O
same	O
as	O
the	O
System/38	B-Device
Machine	O
interface	O
instructions	O
,	O
whereas	O
NMI	O
instructions	O
are	O
lower-level	O
,	O
resembling	O
the	O
W-code	O
intermediate	B-Application
representation	I-Application
format	O
used	O
by	O
IBM	O
's	O
compilers	O
.	O
</s>
<s>
OMI	O
instructions	O
are	O
used	O
by	O
the	O
original	O
AS/400	B-Device
compilers	O
,	O
whereas	O
NMI	O
instructions	O
are	O
used	O
by	O
the	O
Integrated	B-General_Concept
Language	I-General_Concept
Environment	I-General_Concept
compilers	O
.	O
</s>
<s>
The	O
storing	O
of	O
the	O
TIMI	O
instructions	O
alongside	O
the	O
native	O
machine	B-Language
code	I-Language
instructions	O
is	O
known	O
as	O
observability	O
.	O
</s>
<s>
In	O
2008	O
,	O
the	O
release	O
of	O
i5/OS	B-Application
V6R1	O
(	O
later	O
known	O
as	O
IBM	B-Application
i	I-Application
6.1	O
)	O
introduced	O
a	O
number	O
of	O
changes	O
to	O
the	O
TIMI	O
layer	O
which	O
caused	O
problems	O
for	O
third-party	O
software	O
which	O
removed	O
observability	O
from	O
the	O
application	O
objects	O
shipped	O
to	O
customers	O
.	O
</s>
<s>
In	O
addition	O
to	O
containing	O
most	O
of	O
the	O
functionality	O
typically	O
associated	O
with	O
an	O
operating	B-Operating_System
system	I-Operating_System
kernel	I-Operating_System
,	O
it	O
is	O
responsible	O
for	O
translating	O
TIMI	O
instructions	O
into	O
machine	B-Language
code	I-Language
,	O
and	O
it	O
also	O
implements	O
some	O
high	O
level	O
functionality	O
which	O
is	O
exposed	O
through	O
the	O
TIMI	O
,	O
such	O
as	O
IBM	B-Application
i	I-Application
's	O
integrated	O
relational	B-Application
database	I-Application
.	O
</s>
<s>
The	O
SLIC	O
implements	O
IBM	B-Application
i	I-Application
's	O
object-based	O
storage	O
model	O
on	O
top	O
of	O
a	O
single-level	B-Device
store	I-Device
addressing	O
scheme	O
,	O
which	O
does	O
not	O
distinguish	O
between	O
primary	O
and	O
secondary	O
storage	O
,	O
and	O
instead	O
manages	O
all	O
types	O
of	O
storage	O
in	O
a	O
single	O
virtual	B-General_Concept
address	I-General_Concept
space	I-General_Concept
.	O
</s>
<s>
The	O
SLIC	O
is	O
primarily	O
implemented	O
in	O
C++	B-Language
,	O
and	O
replaced	O
the	O
HLIC	O
and	O
VLIC	O
layers	O
used	O
in	O
versions	O
of	O
OS/400	B-Application
prior	O
to	O
V3R6	O
.	O
</s>
<s>
The	O
XPF	O
consists	O
of	O
the	O
code	O
which	O
implements	O
the	O
hardware-independent	O
components	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
,	O
which	O
are	O
compiled	O
into	O
TIMI	O
instructions	O
.	O
</s>
<s>
Components	O
of	O
the	O
XPF	O
include	O
the	O
user	O
interface	O
,	O
the	O
Control	B-Operating_System
Language	I-Operating_System
,	O
data	O
management	O
and	O
query	O
utilities	O
,	O
development	O
tools	O
and	O
system	O
management	O
utilities	O
.	O
</s>
<s>
The	O
XPF	O
also	O
contains	O
the	O
System/36	B-Device
Environment	O
and	O
System/38	B-Device
Environment	O
,	O
which	O
provide	O
backwards	O
compatibility	O
APIs	O
and	O
utilities	O
for	O
applications	O
and	O
data	O
migrated	O
from	O
SSP	B-Operating_System
and	O
CPF	B-Operating_System
systems	O
.	O
</s>
<s>
The	O
XPF	O
is	O
IBM	O
's	O
internal	O
name	O
for	O
this	O
layer	O
,	O
and	O
as	O
the	O
name	O
suggests	O
,	O
began	O
as	O
an	O
evolution	O
of	O
the	O
System/38	B-Device
Control	B-Operating_System
Program	I-Operating_System
Facility	I-Operating_System
.	O
</s>
<s>
PASE	O
(	O
Portable	O
Applications	O
Solutions	O
Environment	O
)	O
provides	O
binary	B-General_Concept
compatibility	I-General_Concept
for	O
user	B-Operating_System
mode	I-Operating_System
AIX	B-Application
executables	B-Application
which	O
do	O
not	O
interact	O
directly	O
with	O
the	O
AIX	B-Application
kernel	B-Operating_System
,	O
and	O
supports	O
the	O
32-bit	O
and	O
64-bit	O
AIX	B-Application
Application	B-Operating_System
Binary	I-Operating_System
Interfaces	I-Operating_System
.	O
</s>
<s>
PASE	O
was	O
first	O
included	O
in	O
a	O
limited	O
and	O
undocumented	O
form	O
in	O
the	O
V4R3	O
release	O
of	O
OS/400	B-Application
to	O
support	O
a	O
port	O
of	O
Smalltalk	B-Application
.	O
</s>
<s>
PASE	O
consists	O
of	O
the	O
AIX	B-Application
userspace	B-Operating_System
running	O
on	O
top	O
of	O
a	O
system	O
call	O
interface	O
implemented	O
by	O
the	O
SLIC	O
.	O
</s>
<s>
The	O
system	O
call	O
interfaces	O
allows	O
interoperability	O
between	O
PASE	O
and	O
native	O
IBM	B-Application
i	I-Application
applications	O
,	O
for	O
example	O
,	O
PASE	O
applications	O
can	O
access	O
the	O
integrated	O
database	O
,	O
or	O
call	O
native	O
IBM	B-Application
i	I-Application
applications	O
,	O
and	O
vice	O
versa	O
.	O
</s>
<s>
During	O
the	O
creation	O
of	O
PASE	O
,	O
a	O
new	O
type	O
of	O
single	O
level	O
storage	O
object	O
named	O
a	O
Teraspace	O
was	O
added	O
to	O
the	O
operating	B-General_Concept
system	I-General_Concept
,	O
which	O
allows	O
each	O
PASE	O
process	O
to	O
have	O
a	O
private	O
1TiB	O
space	O
which	O
is	O
addressed	O
with	O
64-bit	O
pointers	O
.	O
</s>
<s>
This	O
was	O
necessary	O
since	O
all	O
IBM	B-Application
i	I-Application
jobs	O
(	O
i.e.	O
</s>
<s>
processes	O
)	O
typically	O
share	O
the	O
same	O
address	B-General_Concept
space	I-General_Concept
.	O
</s>
<s>
PASE	O
applications	O
do	O
not	O
use	O
the	O
hardware-independent	O
TIMI	O
instructions	O
,	O
and	O
are	O
instead	O
compiled	O
directly	O
to	O
Power	O
machine	B-Language
code	I-Language
.	O
</s>
<s>
PASE	O
is	O
distinct	O
from	O
the	O
Qshell	B-Operating_System
environment	O
,	O
which	O
is	O
an	O
implementation	O
of	O
a	O
Unix	B-Application
shell	O
and	O
associated	O
utilities	O
built	O
on	O
top	O
of	O
IBM	B-Application
i	I-Application
's	O
native	O
POSIX-compatible	O
APIs	O
.	O
</s>
<s>
Introduced	O
in	O
1994	O
,	O
the	O
Advanced/36	O
platform	O
ran	O
unmodified	O
System/36	B-Device
applications	O
and	O
the	O
SSP	B-Operating_System
operating	B-General_Concept
system	I-General_Concept
in	O
emulation	O
on	O
top	O
of	O
the	O
OS/400	B-Application
SLIC	O
using	O
hardware	O
which	O
was	O
mostly	O
identical	O
to	O
that	O
of	O
contemporary	O
AS/400	B-Device
systems	O
.	O
</s>
<s>
This	O
functionality	O
was	O
incorporated	O
into	O
OS/400	B-Application
itself	O
from	O
V3R6	O
through	O
V4R4	O
,	O
making	O
it	O
possible	O
to	O
run	O
up	O
to	O
four	O
System/36	B-Device
"	O
virtual	B-Architecture
machines	I-Architecture
"	O
(	O
to	O
use	O
IBM	O
's	O
term	O
)	O
using	O
the	O
so-called	O
Advanced	O
36	O
Machine	O
feature	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
The	O
Advanced	O
36	O
Machine	O
feature	O
is	O
distinct	O
from	O
the	O
System/36	B-Device
Environment	O
introduced	O
in	O
the	O
initial	O
OS/400	B-Application
release	O
and	O
still	O
supported	O
in	O
current	O
IBM	B-Application
i	I-Application
versions	O
.	O
</s>
<s>
Prior	O
to	O
the	O
Advanced/36	O
,	O
the	O
System/36	B-Device
line	O
used	O
two	O
different	O
processors	O
in	O
each	O
system	O
-	O
the	O
Main	O
Storage	O
Processor	O
(	O
MSP	O
)	O
which	O
ran	O
most	O
of	O
the	O
SSP	B-Operating_System
operating	B-General_Concept
system	I-General_Concept
as	O
well	O
as	O
user	O
code	O
,	O
and	O
the	O
Control	O
Storage	O
Processor	O
(	O
CSP	O
)	O
which	O
ran	O
so-called	O
"	O
microcode	O
"	O
which	O
implemented	O
core	O
operating	B-General_Concept
system	I-General_Concept
functionality	O
as	O
well	O
as	O
I/O	B-General_Concept
.	O
</s>
<s>
Even	O
with	O
the	O
overhead	O
of	O
emulation	O
,	O
the	O
Advanced/36	O
systems	O
were	O
significantly	O
faster	O
than	O
the	O
original	O
System/36	B-Device
systems	O
they	O
replaced	O
due	O
to	O
the	O
performance	O
of	O
their	O
PowerPC	O
AS	O
processors	O
.	O
</s>
<s>
IBM	B-Application
i	I-Application
features	O
an	O
integrated	O
relational	B-Application
database	I-Application
currently	O
known	O
as	O
IBM	B-Application
Db2	I-Application
for	I-Application
IBM	I-Application
i	I-Application
.	O
</s>
<s>
The	O
database	O
evolved	O
from	O
the	O
non-relational	O
System/38	B-Device
database	O
,	O
gaining	O
support	O
for	O
the	O
relational	O
model	O
and	O
SQL	B-Language
.	O
</s>
<s>
It	O
was	O
given	O
the	O
name	O
DB2/400	B-Application
in	O
1994	O
to	O
indicate	O
comparable	O
functionality	O
to	O
IBM	O
's	O
other	O
commercial	O
databases	O
.	O
</s>
<s>
Despite	O
the	O
Db2	B-Application
branding	O
,	O
Db2	B-Application
for	O
IBM	B-Application
i	I-Application
is	O
an	O
entirely	O
separate	O
codebase	O
to	O
Db2	B-Application
on	O
other	O
platforms	O
,	O
and	O
is	O
tightly	O
integrated	O
into	O
the	O
SLIC	O
layer	O
of	O
IBM	B-Application
i	I-Application
as	O
opposed	O
to	O
being	O
an	O
optional	O
product	O
.	O
</s>
<s>
IBM	B-Application
i	I-Application
provides	O
two	O
mechanisms	O
for	O
accessing	O
the	O
integrated	O
database	O
-	O
the	O
so-called	O
native	O
interface	O
,	O
which	O
is	O
based	O
on	O
the	O
database	O
access	O
model	O
of	O
the	O
System/38	B-Device
,	O
and	O
SQL	B-Language
.	O
</s>
<s>
Certain	O
Db2	B-Application
for	I-Application
i	I-Application
features	O
such	O
as	O
object-relational	B-General_Concept
database	I-General_Concept
management	I-General_Concept
require	O
SQL	B-Language
and	O
cannot	O
be	O
accessed	O
through	O
the	O
native	O
interface	O
.	O
</s>
<s>
IBM	B-Application
i	I-Application
has	O
two	O
separate	O
query	B-Language
optimizers	I-Language
known	O
as	O
the	O
Classic	O
Query	O
Engine	O
(	O
CQE	O
)	O
and	O
SQL	B-Language
Query	O
Engine	O
(	O
SQE	O
)	O
.	O
</s>
<s>
Remote	O
access	O
through	O
the	O
native	O
interface	O
and	O
SQL	B-Language
is	O
provided	O
by	O
the	O
Distributed	B-Operating_System
Data	I-Operating_System
Management	I-Operating_System
Architecture	I-Operating_System
(	O
DDM	O
)	O
and	O
Distributed	B-Language
Relational	I-Language
Database	I-Language
Architecture	I-Language
respectively	O
.	O
</s>
<s>
A	O
storage	O
engine	O
for	O
MySQL	B-Application
and	O
MariaDB	B-Application
named	O
IBMDB2I	O
allows	O
applications	O
designed	O
for	O
those	O
databases	O
to	O
use	O
Db2	B-Application
for	I-Application
i	I-Application
as	O
a	O
backing	O
store	O
.	O
</s>
<s>
Other	O
open	O
source	O
databases	O
have	O
been	O
ported	O
to	O
IBM	B-Application
i	I-Application
,	O
including	O
PostgreSQL	B-Application
,	O
MongoDB	B-Application
and	O
Redis	B-Operating_System
.	O
</s>
<s>
These	O
databases	O
run	O
on	O
the	O
PASE	O
environment	O
,	O
and	O
are	O
independent	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
's	O
integrated	O
database	O
features	O
.	O
</s>
<s>
IBM	B-Application
i	I-Application
supports	O
TCP/IP	B-Protocol
networking	O
in	O
addition	O
to	O
the	O
proprietary	B-Application
IBM	B-Architecture
Systems	I-Architecture
Network	I-Architecture
Architecture	I-Architecture
.	O
</s>
<s>
IBM	B-Application
i	I-Application
systems	O
were	O
historically	O
accessed	O
and	O
managed	O
through	O
IBM	B-Device
5250	I-Device
terminals	O
attached	O
to	O
the	O
system	O
with	O
twinax	O
cabling	O
.	O
</s>
<s>
With	O
the	O
decline	O
of	O
dedicated	O
terminal	O
hardware	O
,	O
modern	O
IBM	B-Application
i	I-Application
systems	O
are	O
typically	O
accessed	O
through	O
5250	O
terminal	B-Application
emulators	I-Application
.	O
</s>
<s>
IBM	O
provides	O
two	O
terminal	B-Application
emulator	I-Application
products	O
for	O
IBM	B-Application
i	I-Application
:	O
</s>
<s>
IBM	B-Application
i	I-Application
Access	O
Client	O
Solutions	O
is	O
a	O
Java-based	O
client	O
that	O
runs	O
on	O
Linux	B-Application
,	O
macOS	B-Application
and	O
Windows	B-Application
to	O
provide	O
5250	O
emulation	O
.	O
</s>
<s>
IBM	B-Application
i	I-Application
Access	O
for	O
Web/Mobile	O
provides	O
web-based	O
5250	O
emulation	O
.	O
</s>
<s>
Some	O
of	O
the	O
open	O
source	O
applications	O
ported	O
to	O
IBM	B-Application
i	I-Application
include	O
:	O
</s>
<s>
Open	O
source	O
software	O
for	O
IBM	B-Application
i	I-Application
is	O
typically	O
packaged	O
using	O
the	O
RPM	B-Application
package	I-Application
format	O
,	O
and	O
installed	O
with	O
the	O
YUM	B-Application
package	I-Application
manager	I-Application
.	O
</s>
<s>
YUM	B-Application
and	O
RPM	B-Application
replaced	O
the	O
5733-OPS	O
product	O
,	O
which	O
was	O
previously	O
used	O
to	O
install	O
open	O
source	O
software	O
on	O
IBM	B-Application
i	I-Application
.	O
</s>
<s>
Ports	O
of	O
open	O
source	O
software	O
to	O
IBM	B-Application
i	I-Application
typically	O
target	O
PASE	O
instead	O
of	O
the	O
native	O
IBM	B-Application
i	I-Application
APIs	O
in	O
order	O
to	O
simplify	O
porting	O
.	O
</s>
<s>
Programming	O
languages	O
available	O
from	O
IBM	O
for	O
IBM	B-Application
i	I-Application
include	O
RPG	B-Language
,	O
Control	B-Operating_System
Language	I-Operating_System
,	O
C	B-Language
,	O
C++	B-Language
,	O
Java	B-Language
,	O
EGL	B-Language
,	O
COBOL	B-Application
,	O
and	O
REXX	B-Language
.	O
</s>
<s>
Compilers	O
were	O
previously	O
available	O
for	O
Pascal	B-Application
,	O
BASIC	O
,	O
PL/I	B-Language
and	O
Smalltalk	B-Application
but	O
have	O
since	O
been	O
discontinued	O
.	O
</s>
<s>
The	O
Integrated	B-General_Concept
Language	I-General_Concept
Environment	I-General_Concept
(	O
ILE	O
)	O
allows	O
programs	O
from	O
ILE	O
compatible	O
languages	O
(	O
C	B-Language
,	O
C++	B-Language
,	O
COBOL	B-Application
,	O
RPG	B-Language
,	O
and	O
CL	B-Operating_System
)	O
,	O
to	O
be	O
bound	O
into	O
the	O
same	O
executable	B-Application
and	O
call	O
procedures	O
written	O
in	O
any	O
of	O
the	O
other	O
ILE	O
languages	O
.	O
</s>
<s>
When	O
PASE	O
was	O
introduced	O
,	O
it	O
was	O
necessary	O
to	O
compile	O
code	O
for	O
PASE	O
on	O
an	O
AIX	B-Application
system	O
.	O
</s>
<s>
This	O
requirement	O
was	O
removed	O
in	O
OS/400	B-Application
V5R2	O
when	O
it	O
became	O
possible	O
to	O
compile	O
code	O
using	O
the	O
IBM	B-Language
XL	I-Language
compiler	I-Language
suite	I-Language
inside	O
PASE	O
itself	O
.	O
</s>
<s>
Since	O
then	O
,	O
other	O
compilers	O
have	O
been	O
ported	O
to	O
PASE	O
,	O
including	O
gcc	B-Application
.	O
</s>
<s>
Certain	O
development	O
tools	O
for	O
IBM	B-Application
i	I-Application
run	O
on	O
top	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
itself	O
,	O
such	O
as	O
the	O
Source	O
Edit	O
Utility	O
(	O
SEU	O
)	O
text	B-Application
editor	I-Application
and	O
Programming	B-Device
Development	I-Device
Manager	I-Device
.	O
</s>
<s>
IBM	O
also	O
provides	O
an	O
Eclipse-based	O
integrated	B-Application
development	I-Application
environment	I-Application
(	O
IDE	O
)	O
for	O
IBM	B-Application
i	I-Application
named	O
IBM	O
Rational	O
Developer	O
for	O
i	O
which	O
runs	O
on	O
developer	O
workstations	O
instead	O
of	O
IBM	B-Application
i	I-Application
.	O
</s>
<s>
Prior	O
to	O
the	O
Eclipse-based	O
IDE	O
,	O
IBM	O
provided	O
an	O
IDE	O
based	O
on	O
WorkFrame/2	O
which	O
ran	O
on	O
OS/2	B-Application
named	O
CODE/400	O
and	O
an	O
IDE	O
based	O
on	O
VisualAge	B-Language
which	O
ran	O
on	O
Microsoft	B-Application
Windows	I-Application
systems	O
.	O
</s>
<s>
IBM	B-Application
i	I-Application
uses	O
EBCDIC	B-Language
as	O
the	O
default	O
character	B-General_Concept
encoding	I-General_Concept
,	O
but	O
also	O
provides	O
support	O
for	O
ASCII	B-Protocol
,	O
UCS-2	O
and	O
UTF-16	O
.	O
</s>
<s>
In	O
IBM	B-Application
i	I-Application
,	O
disk	O
drives	O
may	O
be	O
grouped	O
into	O
an	O
auxiliary	O
storage	O
pool	O
(	O
ASP	O
)	O
in	O
order	O
to	O
organize	O
data	O
to	O
limit	O
the	O
impact	O
of	O
storage-device	O
failures	O
and	O
to	O
reduce	O
recovery	O
time	O
.	O
</s>
<s>
The	O
concept	O
of	O
IBM	B-Application
i	I-Application
pools	O
is	O
similar	O
to	O
the	O
Unix/Linux	O
concept	O
of	O
volume	B-Application
groups	I-Application
;	O
however	O
,	O
with	O
IBM	B-Application
i	I-Application
it	O
is	O
typical	O
for	O
all	O
disk	O
drives	O
to	O
be	O
assigned	O
to	O
a	O
single	O
ASP	O
.	O
</s>
<s>
Security	O
in	O
IBM	B-Application
i	I-Application
is	O
defined	O
in	O
terms	O
of	O
authorities	O
,	O
which	O
represents	O
the	O
permission	O
to	O
carry	O
out	O
a	O
specific	O
action	O
on	O
a	O
specific	O
object	O
.	O
</s>
<s>
IBM	B-Application
i	I-Application
ships	O
with	O
a	O
default	O
user	O
profile	O
for	O
each	O
user	O
class	O
,	O
and	O
the	O
default	O
Security	O
Officer	O
user	O
profile	O
,	O
named	O
QSECOFR	O
,	O
is	O
the	O
closest	O
equivalent	O
to	O
the	O
root	B-Application
user	I-Application
of	O
a	O
Unix-like	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
IBM	B-Application
i	I-Application
can	O
be	O
set	O
to	O
use	O
one	O
of	O
five	O
levels	O
of	O
security	O
,	O
which	O
control	O
the	O
extent	O
to	O
which	O
the	O
operating	B-General_Concept
system	I-General_Concept
's	O
security	O
features	O
are	O
enforced	O
:	O
</s>
<s>
Level	O
40	O
–	O
Access	O
to	O
certain	O
system	O
programs	O
and	O
MI	O
instructions	O
are	O
restricted	O
,	O
and	O
can	O
only	O
be	O
used	O
by	O
operating	B-General_Concept
system	I-General_Concept
code	O
.	O
</s>
<s>
The	O
first	O
three	O
levels	O
correspond	O
to	O
the	O
security	O
levels	O
available	O
in	O
CPF	B-Operating_System
and	O
the	O
initial	O
releases	O
of	O
OS/400	B-Application
.	O
</s>
<s>
Security	O
level	O
40	O
was	O
added	O
in	O
OS/400	B-Application
V1R3	O
and	O
become	O
the	O
default	O
security	O
level	O
for	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
The	O
addition	O
of	O
Level	O
40	O
required	O
the	O
removal	O
of	O
the	O
capability	B-General_Concept
addressing	I-General_Concept
model	O
of	O
the	O
System/38	B-Device
which	O
was	O
also	O
present	O
in	O
earlier	O
releases	O
of	O
OS/400	B-Application
.	O
</s>
<s>
Security	O
level	O
50	O
was	O
added	O
in	O
V2R3	O
when	O
OS/400	B-Application
was	O
certified	O
to	O
TCSEC	O
C2	O
security	O
.	O
</s>
