<s>
PALcode	B-General_Concept
(	O
Privileged	B-General_Concept
Architecture	I-General_Concept
Library	I-General_Concept
code	I-General_Concept
)	O
is	O
the	O
name	O
used	O
by	O
DEC	O
in	O
the	O
Alpha	B-Device
instruction	B-General_Concept
set	I-General_Concept
architecture	I-General_Concept
(	O
ISA	O
)	O
for	O
a	O
set	O
of	O
functions	O
in	O
the	O
System	B-General_Concept
Reference	I-General_Concept
Manual	I-General_Concept
(	O
SRM	O
)	O
or	O
AlphaBIOS	B-Device
firmware	B-Application
,	O
providing	O
a	O
hardware	B-Operating_System
abstraction	I-Operating_System
layer	I-Operating_System
for	O
system	O
software	O
,	O
covering	O
features	O
such	O
as	O
cache	O
management	O
,	O
translation	B-Architecture
lookaside	I-Architecture
buffer	I-Architecture
(	O
TLB	O
)	O
miss	O
handling	O
,	O
interrupt	O
handling	O
,	O
and	O
exception	O
handling	O
.	O
</s>
<s>
It	O
evolved	O
from	O
a	O
feature	O
of	O
the	O
DEC	B-Architecture
PRISM	I-Architecture
architecture	O
named	O
Epicode	O
.	O
</s>
<s>
PALcode	B-General_Concept
is	O
Alpha	B-Device
machine	O
code	O
,	O
running	O
in	O
a	O
special	O
mode	O
that	O
also	O
allows	O
access	O
to	O
internal	O
registers	O
specific	O
to	O
the	O
particular	O
Alpha	B-Device
processor	I-Device
implementation	O
.	O
</s>
<s>
Thus	O
,	O
it	O
is	O
somewhere	O
between	O
the	O
role	O
of	O
microcode	B-Device
and	O
of	O
a	O
hardware	O
emulator	B-Application
.	O
</s>
<s>
PALcode	B-General_Concept
is	O
operating	O
system-specific	O
,	O
so	O
different	O
versions	O
of	O
PALcode	B-General_Concept
are	O
required	O
by	O
OpenVMS	B-Operating_System
,	O
Tru64	B-Operating_System
UNIX	I-Operating_System
,	O
and	O
Windows	B-Device
NT	I-Device
.	O
</s>
<s>
Tru64	B-Operating_System
UNIX	I-Operating_System
PALcode	B-General_Concept
is	O
also	O
used	O
by	O
NetBSD	B-Device
,	O
FreeBSD	B-Operating_System
,	O
OpenBSD	B-Operating_System
and	O
Linux	B-Application
.	O
</s>
