<s>
In	O
computer	B-General_Concept
architecture	I-General_Concept
,	O
millicode	B-General_Concept
is	O
a	O
higher	O
level	O
of	O
microcode	B-Device
used	O
to	O
implement	O
the	O
instruction	B-General_Concept
set	I-General_Concept
of	O
a	O
computer	O
.	O
</s>
<s>
Millicode	B-General_Concept
runs	O
on	O
top	O
of	O
the	O
microcoded	B-Device
instructions	O
and	O
uses	O
those	O
instructions	O
to	O
implement	O
more	O
complex	O
instructions	O
visible	O
to	O
the	O
user	O
of	O
the	O
system	O
.	O
</s>
<s>
Implementation	O
of	O
millicode	B-General_Concept
requires	O
a	O
special	O
processor	O
mode	O
called	O
millimode	B-General_Concept
that	O
provides	O
its	O
own	O
set	O
of	O
registers	O
,	O
and	O
possibly	O
its	O
own	O
special	O
instructions	O
invisible	O
to	O
the	O
user	O
.	O
</s>
<s>
IBM	O
invented	O
both	O
the	O
concept	O
and	O
the	O
term	O
millicode	B-General_Concept
for	O
the	O
System/390	O
9672-G4	O
processor	O
in	O
1997	O
.	O
</s>
<s>
The	O
following	O
are	O
cited	O
as	O
advantages	O
of	O
millicode	B-General_Concept
:	O
</s>
<s>
More	O
complex	O
instructions	O
can	O
easily	O
be	O
constructed	O
from	O
several	O
millicode	B-General_Concept
instructions	O
.	O
</s>
<s>
Millicode	B-General_Concept
instructions	O
can	O
bypass	O
CPU	B-General_Concept
cache	I-General_Concept
to	O
improve	O
performance	O
.	O
</s>
<s>
Millicode	B-General_Concept
can	O
execute	O
instructions	O
at	O
a	O
higher	O
privilege	O
level	O
without	O
involving	O
the	O
operating	O
system	O
.	O
</s>
<s>
Millicode	B-General_Concept
can	O
provide	O
a	O
complex	O
instruction	O
as	O
if	O
it	O
were	O
a	O
subroutine	O
,	O
making	O
user	O
code	O
smaller	O
.	O
</s>
<s>
The	O
"	O
i370	O
"	O
code	O
for	O
the	O
"	O
Capitol	O
"	O
chipset	O
used	O
in	O
some	O
ES/9370	B-Device
models	O
was	O
similar	O
to	O
millicode	B-General_Concept
,	O
in	O
that	O
it	O
was	O
written	O
as	O
a	O
combination	O
of	O
System/370	B-Device
instructions	O
and	O
code	O
that	O
had	O
access	O
to	O
special	O
hardware	O
features	O
.	O
</s>
