<s>
MICA	O
was	O
the	O
codename	O
of	O
the	O
operating	O
system	O
developed	O
for	O
the	O
DEC	B-Architecture
PRISM	I-Architecture
architecture	O
.	O
</s>
<s>
MICA	O
's	O
design	O
was	O
driven	O
by	O
Digital	O
's	O
need	O
to	O
provide	O
a	O
migration	O
path	O
to	O
PRISM	O
for	O
Digital	O
's	O
VAX/VMS	B-Operating_System
customers	O
,	O
as	O
well	O
as	O
allowing	O
PRISM	O
systems	O
to	O
compete	O
in	O
the	O
increasingly	O
important	O
Unix	O
market	O
.	O
</s>
<s>
MICA	O
attempted	O
to	O
address	O
these	O
requirements	O
by	O
implementing	O
VMS	B-Operating_System
and	O
ULTRIX	B-Operating_System
user	O
interfaces	O
on	O
top	O
of	O
a	O
common	O
kernel	O
that	O
could	O
support	O
the	O
system	B-Operating_System
calls	I-Operating_System
(	O
or	O
"	O
system	O
services	O
"	O
in	O
VMS	B-Operating_System
parlance	O
)	O
,	O
libraries	O
and	O
utilities	O
needed	O
for	O
both	O
environments	O
.	O
</s>
<s>
MICA	O
is	O
most	O
notable	O
for	O
inspiring	O
the	O
design	O
of	O
Windows	B-Device
NT	I-Device
.	O
</s>
<s>
When	O
the	O
PRISM	O
architecture	O
evolved	O
into	O
the	O
DEC	B-Device
Alpha	I-Device
architecture	O
,	O
Digital	O
opted	O
to	O
port	O
OSF/1	B-Operating_System
and	O
VMS	B-Operating_System
to	O
Alpha	B-Device
instead	O
of	O
reusing	O
MICA	O
.	O
</s>
<s>
The	O
original	O
goal	O
for	O
MICA	O
was	O
that	O
all	O
applications	O
would	O
have	O
full	O
and	O
interchangeable	O
access	O
to	O
both	O
the	O
VMS	B-Operating_System
and	O
ULTRIX	B-Operating_System
interfaces	O
,	O
and	O
that	O
a	O
user	O
could	O
choose	O
to	O
log	O
in	O
to	O
an	O
ULTRIX	B-Operating_System
or	O
VMS	B-Operating_System
environment	O
,	O
and	O
run	O
any	O
MICA	O
application	O
from	O
either	O
environment	O
.	O
</s>
<s>
However	O
,	O
it	O
proved	O
to	O
be	O
impossible	O
to	O
provide	O
both	O
full	O
ULTRIX	B-Operating_System
and	O
full	O
VMS	B-Operating_System
compatibility	O
to	O
the	O
same	O
application	O
at	O
the	O
same	O
time	O
,	O
and	O
Digital	O
scrapped	O
this	O
plan	O
in	O
favour	O
of	O
having	O
a	O
separate	O
Unix	O
operating	O
system	O
based	O
on	O
OSF/1	B-Operating_System
(	O
this	O
was	O
variously	O
referred	O
to	O
as	O
PRISM	O
ULTRIX	B-Operating_System
or	O
OZIX	B-Operating_System
)	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
MICA	O
would	O
have	O
served	O
as	O
a	O
portable	O
implementation	O
of	O
a	O
VMS-like	O
operating	O
system	O
,	O
with	O
compatible	O
implementations	O
of	O
DCL	B-Operating_System
,	O
RMS	B-Application
,	O
Files-11	B-Application
,	O
VAXclusters	B-Operating_System
,	O
and	O
the	O
VAX/VMS	B-Operating_System
RTLs	O
and	O
system	O
services	O
.	O
</s>
<s>
Proposals	O
were	O
made	O
for	O
reinstating	O
Unix	O
compatibility	O
in	O
MICA	O
on	O
a	O
per-application	O
basis	O
so	O
that	O
a	O
MICA	O
application	O
could	O
be	O
compiled	O
and	O
linked	O
against	O
the	O
VMS	B-Operating_System
interfaces	O
,	O
or	O
the	O
ULTRIX	B-Operating_System
interfaces	O
,	O
but	O
not	O
both	O
simultaneously	O
.	O
</s>
<s>
MICA	O
was	O
to	O
be	O
written	O
almost	O
entirely	O
in	O
a	O
high-level	B-Language
programming	I-Language
language	I-Language
named	O
PILLAR	O
.	O
</s>
<s>
PILLAR	O
evolved	O
from	O
EPascal	O
(	O
the	O
VAXELN-specific	O
dialect	O
of	O
Pascal	B-Application
)	O
via	O
an	O
interim	O
language	O
called	O
the	O
Systems	O
Implementation	O
Language	O
(	O
SIL	O
)	O
.	O
</s>
<s>
PILLAR	O
would	O
have	O
been	O
backported	O
to	O
VAX/VMS	B-Operating_System
,	O
allowing	O
applications	O
to	O
be	O
developed	O
that	O
could	O
be	O
compiled	O
for	O
both	O
VAX/VMS	B-Operating_System
and	O
MICA	O
.	O
</s>
<s>
A	O
common	O
set	O
of	O
high-level	O
runtime	O
libraries	O
named	O
ARUS	O
(	O
Application	O
Runtime	O
Utility	O
Services	O
)	O
would	O
have	O
further	O
facilitated	O
portability	O
between	O
MICA	O
,	O
OSF/1	B-Operating_System
,	O
VAX/VMS	B-Operating_System
and	O
ULTRIX	B-Operating_System
.	O
</s>
<s>
As	O
part	O
of	O
the	O
PRISM	O
project	O
,	O
a	O
common	O
optimizing	O
compiler	O
backend	O
named	O
GEM	O
was	O
developed	O
(	O
this	O
survived	O
and	O
became	O
the	O
compiler	O
backend	O
for	O
the	O
Alpha	B-Device
and	O
Itanium	O
ports	O
of	O
VMS	B-Operating_System
,	O
as	O
well	O
as	O
Tru64	B-Operating_System
)	O
.	O
</s>
<s>
In	O
addition	O
to	O
PILLAR	O
,	O
Mica	O
provided	O
first-class	O
support	O
for	O
ANSI	O
C	B-Language
in	O
order	O
to	O
support	O
Unix	O
applications	O
.	O
</s>
<s>
An	O
assembler	B-Application
named	O
SPASM	O
(	O
Simplified	O
PRISM	O
Assembler	B-Application
)	O
was	O
intended	O
for	O
the	O
small	O
amount	O
of	O
assembly	O
code	O
needed	O
for	O
the	O
operating	O
system	O
,	O
and	O
would	O
not	O
have	O
been	O
made	O
generally	O
available	O
in	O
order	O
to	O
dissuade	O
customers	O
from	O
developing	O
non-portable	O
software	O
.	O
</s>
<s>
Similarly	O
,	O
an	O
implementation	O
of	O
BLISS	B-Language
was	O
developed	O
for	O
internal	O
use	O
only	O
,	O
in	O
order	O
to	O
allow	O
pre-existing	O
VAX/VMS	B-Operating_System
applications	O
to	O
be	O
ported	O
to	O
MICA	O
.	O
</s>
<s>
MICA	O
would	O
have	O
featured	O
ports	O
or	O
rewrites	O
of	O
many	O
VAX/VMS	B-Operating_System
layered	O
products	O
,	O
including	O
Rdb	B-Application
,	O
VAXset	B-Application
,	O
DECwindows	B-Application
,	O
and	O
most	O
of	O
the	O
compilers	O
available	O
for	O
VAX/VMS	B-Operating_System
.	O
</s>
<s>
When	O
PRISM	O
and	O
MICA	O
were	O
cancelled	O
,	O
Dave	O
Cutler	O
left	O
Digital	O
for	O
Microsoft	O
,	O
where	O
he	O
was	O
put	O
in	O
charge	O
of	O
the	O
development	O
of	O
what	O
became	O
known	O
as	O
Windows	B-Device
NT	I-Device
.	O
</s>
<s>
In	O
addition	O
to	O
the	O
implementation	O
of	O
multiple	O
operating	O
system	O
APIs	O
on	O
top	O
of	O
a	O
common	O
kernel	O
(	O
Win32	B-Library
,	O
OS/2	B-Application
and	O
POSIX	O
in	O
NT	O
's	O
case	O
)	O
MICA	O
and	O
NT	O
shared	O
the	O
separation	O
of	O
the	O
kernel	O
from	O
the	O
executive	O
,	O
the	O
use	O
of	O
an	O
Object	B-General_Concept
Manager	I-General_Concept
as	O
the	O
abstraction	O
for	O
interfacing	O
with	O
operating	O
system	O
data	O
structures	O
,	O
and	O
support	O
for	O
multithreading	B-Operating_System
and	O
symmetric	B-Operating_System
multiprocessing	I-Operating_System
.	O
</s>
<s>
After	O
the	O
cancellation	O
of	O
PRISM	O
,	O
Digital	O
began	O
a	O
project	O
to	O
produce	O
a	O
faster	O
VAX	O
implementation	O
which	O
could	O
run	O
VMS	B-Operating_System
and	O
provide	O
comparable	O
performance	O
to	O
its	O
DECstation	B-Device
line	O
of	O
Unix	O
systems	O
.	O
</s>
<s>
When	O
these	O
attempts	O
failed	O
,	O
the	O
design	O
group	O
concluded	O
that	O
VMS	B-Operating_System
itself	O
could	O
be	O
ported	O
to	O
a	O
PRISM-like	O
architecture	O
.	O
</s>
<s>
This	O
led	O
to	O
the	O
DEC	B-Device
Alpha	I-Device
architecture	O
,	O
and	O
the	O
Alpha	B-Device
port	O
of	O
VMS	B-Operating_System
.	O
</s>
