<s>
PRISM	O
(	O
Parallel	O
Reduced	B-Architecture
Instruction	I-Architecture
Set	I-Architecture
Machine	O
)	O
was	O
a	O
32-bit	O
RISC	B-Architecture
instruction	I-Architecture
set	I-Architecture
architecture	O
(	O
ISA	O
)	O
developed	O
by	O
Digital	O
Equipment	O
Corporation	O
(	O
DEC	O
)	O
.	O
</s>
<s>
This	O
process	O
eventually	O
decided	O
to	O
use	O
the	O
design	O
for	O
a	O
new	O
line	O
of	O
Unix	B-Device
workstations	I-Device
.	O
</s>
<s>
The	O
arithmetic	B-General_Concept
logic	I-General_Concept
unit	I-General_Concept
(	O
ALU	O
)	O
of	O
the	O
microPrism	B-Device
version	O
had	O
completed	O
design	O
in	O
April	O
1988	O
and	O
samples	O
were	O
fabricated	O
,	O
but	O
the	O
design	O
of	O
other	O
components	O
like	O
the	O
floating	B-General_Concept
point	I-General_Concept
unit	I-General_Concept
(	O
FPU	O
)	O
and	O
memory	B-General_Concept
management	I-General_Concept
unit	I-General_Concept
(	O
MMU	O
)	O
were	O
still	O
not	O
complete	O
in	O
the	O
summer	O
when	O
DEC	O
management	O
decided	O
to	O
cancel	O
the	O
project	O
in	O
favor	O
of	O
MIPS-based	O
systems	O
.	O
</s>
<s>
An	O
operating	B-General_Concept
system	I-General_Concept
codenamed	O
MICA	B-Operating_System
was	O
developed	O
for	O
the	O
PRISM	O
architecture	O
,	O
which	O
would	O
have	O
served	O
as	O
a	O
replacement	O
for	O
both	O
VAX/VMS	B-Operating_System
and	O
ULTRIX	B-Operating_System
on	O
PRISM	O
.	O
</s>
<s>
Many	O
of	O
the	O
team	O
members	O
left	O
the	O
company	O
over	O
the	O
next	O
year	O
,	O
notably	O
Dave	O
Cutler	O
who	O
moved	O
to	O
Microsoft	O
and	O
led	O
the	O
development	O
of	O
Windows	B-Device
NT	I-Device
.	O
</s>
<s>
The	O
MIPS-based	O
workstations	B-Device
were	O
moderately	O
successful	O
among	O
DEC	O
's	O
existing	O
Ultrix	B-Operating_System
users	O
but	O
had	O
little	O
success	O
competing	O
against	O
companies	O
like	O
Sun	O
Microsystems	O
.	O
</s>
<s>
Meanwhile	O
,	O
DEC	O
's	O
cash-cow	O
VAX	B-Device
line	O
grew	O
increasingly	O
less	O
performant	O
as	O
new	O
RISC	B-Architecture
designs	O
outperformed	O
even	O
the	O
top-of-the-line	O
VAX	B-Device
9000	I-Device
.	O
</s>
<s>
As	O
the	O
company	O
explored	O
the	O
future	O
of	O
the	O
VAX	B-Device
they	O
concluded	O
that	O
a	O
PRISM-like	O
processor	O
with	O
a	O
few	O
additional	O
changes	O
could	O
address	O
all	O
of	O
these	O
markets	O
.	O
</s>
<s>
Starting	O
where	O
PRISM	O
left	O
off	O
,	O
the	O
DEC	B-Device
Alpha	I-Device
program	O
started	O
in	O
1989	O
.	O
</s>
<s>
Introduced	O
in	O
1977	O
,	O
the	O
VAX	B-Device
was	O
a	O
runaway	O
success	O
for	O
DEC	O
,	O
cementing	O
its	O
place	O
as	O
the	O
world	O
's	O
#2	O
computer	O
vendor	O
behind	O
IBM	O
.	O
</s>
<s>
The	O
VAX	B-Device
was	O
noted	O
for	O
its	O
rich	O
instruction	B-General_Concept
set	I-General_Concept
architecture	I-General_Concept
(	O
ISA	O
)	O
,	O
which	O
was	O
implemented	O
in	O
complex	O
microcode	B-Device
.	O
</s>
<s>
The	O
VMS	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
was	O
layered	O
on	O
top	O
of	O
this	O
ISA	O
,	O
which	O
drove	O
it	O
to	O
have	O
certain	O
requirements	O
for	O
interrupt	B-Application
handling	I-Application
and	O
the	O
memory	O
model	O
used	O
for	O
memory	B-Architecture
paging	I-Architecture
.	O
</s>
<s>
By	O
the	O
early	O
1980s	O
,	O
VAX	B-Device
systems	O
had	O
become	O
"	O
the	O
computing	O
hub	O
of	O
many	O
technology-driven	O
companies	O
,	O
sending	O
spokes	O
of	O
RS-232	O
cables	O
out	O
to	O
a	O
rim	O
of	O
VT-100	O
terminals	O
that	O
kept	O
the	O
science	O
and	O
engineering	O
departments	O
rolling.	O
"	O
</s>
<s>
This	O
happy	O
situation	O
was	O
upset	O
by	O
the	O
relentless	O
improvement	O
of	O
semiconductor	B-Architecture
manufacturing	I-Architecture
as	O
encoded	O
by	O
Moore	O
's	O
Law	O
;	O
by	O
the	O
early	O
1980s	O
there	O
were	O
a	O
number	O
of	O
capable	O
32-bit	O
single-chip	O
microprocessors	B-Architecture
with	O
performance	O
similar	O
to	O
early	O
VAX	B-Device
machines	O
yet	O
able	O
to	O
fit	O
into	O
a	O
desktop	O
pizza	O
box	O
form	O
factor	O
.	O
</s>
<s>
Companies	O
like	O
Sun	O
Microsystems	O
introduced	O
Motorola	O
68000	O
series-based	O
Unix	B-Device
workstations	I-Device
that	O
could	O
replace	O
a	O
huge	O
multi-user	O
VAX	B-Device
machine	O
with	O
one	O
that	O
provided	O
even	O
more	O
performance	O
but	O
was	O
inexpensive	O
enough	O
to	O
be	O
purchased	O
for	O
every	O
user	O
that	O
required	O
one	O
.	O
</s>
<s>
While	O
DEC	O
's	O
own	O
microprocessor	B-Architecture
teams	O
were	O
introducing	O
a	O
series	O
of	O
VAX	B-Device
implementations	O
at	O
lower	O
price-points	O
,	O
the	O
price-performance	O
ratio	O
of	O
their	O
systems	O
continued	O
to	O
be	O
eroded	O
.	O
</s>
<s>
The	O
hundreds	O
of	O
other	O
instructions	O
in	O
their	O
ISAs	O
,	O
implemented	O
using	O
microcode	B-Device
,	O
went	O
almost	O
entirely	O
unused	O
.	O
</s>
<s>
The	O
presence	O
of	O
the	O
microcode	B-Device
introduced	O
a	O
delay	O
when	O
the	O
instructions	O
were	O
decoded	O
,	O
so	O
even	O
when	O
one	O
called	O
one	O
of	O
those	O
five	O
instructions	O
directly	O
,	O
it	O
ran	O
slower	O
than	O
it	O
could	O
if	O
there	O
was	O
no	O
microcode	B-Device
.	O
</s>
<s>
This	O
led	O
to	O
the	O
IBM	B-Device
801	I-Device
design	O
,	O
the	O
first	O
modern	O
RISC	B-Architecture
processor	I-Architecture
.	O
</s>
<s>
Around	O
the	O
same	O
time	O
,	O
in	O
1979	O
,	O
Dave	O
Patterson	O
was	O
sent	O
on	O
a	O
sabbatical	O
from	O
University	O
of	O
California	O
,	O
Berkeley	O
to	O
help	O
DEC	O
's	O
west-coast	O
team	O
improve	O
the	O
VAX	B-Device
microcode	B-Device
.	O
</s>
<s>
He	O
first	O
wrote	O
a	O
paper	O
on	O
ways	O
to	O
improve	O
microcoding	B-Device
,	O
but	O
later	O
changed	O
his	O
mind	O
and	O
decided	O
microcode	B-Device
itself	O
was	O
the	O
problem	O
.	O
</s>
<s>
He	O
soon	O
started	O
the	O
Berkeley	B-General_Concept
RISC	I-General_Concept
project	O
.	O
</s>
<s>
The	O
emergence	O
of	O
RISC	B-Architecture
sparked	O
off	O
a	O
long-running	O
debate	O
within	O
the	O
computer	O
industry	O
about	O
its	O
merits	O
;	O
when	O
Patterson	O
first	O
outlined	O
his	O
arguments	O
for	O
the	O
concept	O
in	O
1980	O
,	O
a	O
dismissive	O
dissenting	O
opinion	O
was	O
published	O
by	O
DEC	O
.	O
</s>
<s>
By	O
the	O
mid-1980s	O
practically	O
every	O
company	O
with	O
a	O
processor	O
design	O
arm	O
began	O
exploring	O
the	O
RISC	B-Architecture
approach	O
.	O
</s>
<s>
In	O
the	O
period	O
from	O
1982	O
to	O
1985	O
,	O
no	O
fewer	O
than	O
four	O
attempts	O
were	O
made	O
to	O
create	O
a	O
RISC	B-Architecture
chip	O
at	O
different	O
DEC	O
divisions	O
.	O
</s>
<s>
Titan	O
from	O
DEC	O
's	O
Western	O
Research	O
Laboratory	O
(	O
WRL	O
)	O
in	O
Palo	O
Alto	O
,	O
California	O
was	O
a	O
high-performance	O
ECL	B-General_Concept
based	O
design	O
that	O
started	O
in	O
1982	O
,	O
intended	O
to	O
run	O
Unix	B-Application
.	O
</s>
<s>
SAFE	O
(	O
Streamlined	O
Architecture	O
for	O
Fast	O
Execution	O
)	O
was	O
a	O
64-bit	B-Device
design	O
that	O
started	O
the	O
same	O
year	O
,	O
designed	O
by	O
Alan	O
Kotok	O
(	O
of	O
Spacewar	B-Application
!	I-Application
</s>
<s>
fame	O
)	O
and	O
Dave	O
Orbits	O
and	O
intended	O
to	O
run	O
VMS	B-Operating_System
.	O
</s>
<s>
HR-32	O
(	O
Hudson	O
,	O
RISC	B-Architecture
,	O
32-bit	O
)	O
started	O
in	O
1984	O
by	O
Rich	O
Witek	O
and	O
Dan	O
Dobberpuhl	O
at	O
the	O
Hudson	O
,	O
MA	O
fab	O
,	O
intended	O
to	O
be	O
used	O
as	O
a	O
co-processor	B-General_Concept
in	O
VAX	B-Device
machine	O
.	O
</s>
<s>
Eventually	O
,	O
Cutler	O
was	O
asked	O
to	O
define	O
a	O
single	O
RISC	B-Architecture
project	O
in	O
1985	O
,	O
selecting	O
Rich	O
Witek	O
as	O
the	O
chief	O
architect	O
.	O
</s>
<s>
Through	O
this	O
early	O
period	O
,	O
there	O
were	O
constant	O
changes	O
in	O
the	O
design	O
as	O
debates	O
within	O
the	O
company	O
argued	O
over	O
whether	O
it	O
should	O
be	O
32	O
-	O
or	O
64-bit	B-Device
,	O
aimed	O
at	O
a	O
commercial	O
or	O
technical	O
workload	O
,	O
and	O
so	O
forth	O
.	O
</s>
<s>
At	O
the	O
time	O
,	O
the	O
decision	O
was	O
made	O
to	O
produce	O
two	O
versions	O
of	O
the	O
basic	O
concept	O
,	O
DECwest	O
worked	O
on	O
a	O
"	O
high-end	O
"	O
ECL	B-General_Concept
implementation	O
known	O
as	O
Crystal	O
,	O
while	O
the	O
Semiconductor	O
Advanced	O
Development	O
team	O
worked	O
on	O
microPRISM	B-Device
,	O
a	O
CMOS	B-Device
version	O
.	O
</s>
<s>
This	O
work	O
was	O
98%	O
done	O
1985	O
–	O
86	O
and	O
was	O
heavily	O
supported	O
by	O
simulations	O
by	O
Pete	O
Benoit	O
on	O
a	O
large	O
VAXcluster	B-Operating_System
.	O
</s>
<s>
Through	O
this	O
era	O
there	O
was	O
still	O
considerable	O
scepticism	O
on	O
the	O
part	O
of	O
DEC	O
engineering	O
as	O
a	O
whole	O
about	O
whether	O
RISC	B-Architecture
was	O
really	O
faster	O
,	O
or	O
simply	O
faster	O
on	O
the	O
trivial	O
five-line	O
programs	O
being	O
used	O
to	O
demonstrate	O
its	O
performance	O
.	O
</s>
<s>
Based	O
on	O
the	O
Crystal	O
design	O
,	O
in	O
1986	O
it	O
was	O
compared	O
to	O
the	O
then-fastest	O
machine	O
in	O
development	O
,	O
the	O
VAX	B-Device
8800	I-Device
.	O
</s>
<s>
The	O
conclusion	O
was	O
clear	O
:	O
for	O
any	O
given	O
amount	O
of	O
investment	O
,	O
the	O
RISC	B-Architecture
designs	O
would	O
outperform	O
a	O
VAX	B-Device
by	O
2-to-1	O
.	O
</s>
<s>
In	O
the	O
middle	O
of	O
1987	O
,	O
the	O
decision	O
was	O
made	O
that	O
both	O
designs	O
be	O
64-bit	B-Device
,	O
although	O
this	O
lasted	O
only	O
a	O
few	O
weeks	O
.	O
</s>
<s>
In	O
October	O
1987	O
,	O
Sun	O
introduced	O
the	O
Sun-4	B-Device
.	O
</s>
<s>
Powered	O
by	O
a	O
16MHz	O
SPARC	B-Architecture
,	O
a	O
commercial	O
version	O
of	O
Patterson	O
's	O
RISC	B-Architecture
design	O
,	O
it	O
ran	O
four	O
times	O
as	O
fast	O
as	O
their	O
previous	O
top-end	O
Sun-3	O
using	O
a	O
20MHz	O
Motorola	B-Device
68020	I-Device
.	O
</s>
<s>
With	O
this	O
release	O
,	O
DEC	O
once	O
again	O
changed	O
the	O
target	O
for	O
PRISM	O
,	O
aiming	O
it	O
solely	O
at	O
the	O
workstation	B-Device
space	O
.	O
</s>
<s>
This	O
resulted	O
in	O
the	O
microPRISM	B-Device
being	O
respecified	O
as	O
a	O
32-bit	O
system	O
while	O
the	O
Crystal	O
project	O
was	O
canceled	O
.	O
</s>
<s>
By	O
early	O
1988	O
the	O
system	O
was	O
still	O
not	O
complete	O
;	O
the	O
CPU	O
design	O
was	O
nearly	O
complete	O
,	O
but	O
the	O
FPU	O
and	O
MMU	O
,	O
both	O
based	O
on	O
the	O
contemporary	O
Rigel	B-Device
chipset	I-Device
for	O
the	O
VAX	B-Device
,	O
were	O
still	O
being	O
designed	O
.	O
</s>
<s>
As	O
newer	O
RISC-based	B-Architecture
workstations	B-Device
were	O
introduced	O
,	O
the	O
performance	O
benefit	O
of	O
the	O
VAX	B-Device
was	O
constantly	O
eroded	O
,	O
and	O
the	O
price/performance	O
ratio	O
completely	O
undermined	O
.	O
</s>
<s>
Some	O
advocated	O
moving	O
the	O
VAX	B-Device
into	O
the	O
high-end	O
,	O
abandoning	O
the	O
low-end	O
to	O
the	O
workstation	B-Device
vendors	O
like	O
Sun	O
.	O
</s>
<s>
This	O
led	O
to	O
the	O
VAX	B-Device
9000	I-Device
program	O
,	O
which	O
was	O
referred	O
to	O
internally	O
as	O
the	O
"	O
IBM	O
killer	O
"	O
.	O
</s>
<s>
Others	O
suggested	O
moving	O
into	O
the	O
workstation	B-Device
market	O
using	O
PRISM	O
or	O
a	O
commodity	O
processor	O
.	O
</s>
<s>
Still	O
others	O
suggested	O
re-implementing	O
the	O
VAX	B-Device
on	O
a	O
RISC	B-Architecture
processor	I-Architecture
.	O
</s>
<s>
Frustrated	O
with	O
the	O
growing	O
number	O
of	O
losses	O
to	O
cheaper	O
faster	O
competitive	O
machines	O
,	O
independently	O
,	O
a	O
small	O
skunkworks	O
group	O
in	O
Palo	O
Alto	O
,	O
outside	O
of	O
Central	O
Engineering	O
,	O
focused	O
on	O
workstations	B-Device
and	O
UNIX/Ultrix	O
,	O
entertained	O
the	O
idea	O
of	O
using	O
an	O
off-the-shelf	O
RISC	B-Architecture
processor	I-Architecture
to	O
build	O
a	O
new	O
family	O
of	O
workstations	B-Device
.	O
</s>
<s>
The	O
group	O
carried	O
out	O
due	O
diligence	O
,	O
eventually	O
choosing	O
the	O
MIPS	B-Device
R2000	I-Device
.	O
</s>
<s>
This	O
group	O
acquired	O
a	O
development	O
machine	O
and	O
prototyped	O
a	O
port	O
of	O
Ultrix	B-Operating_System
to	O
the	O
system	O
.	O
</s>
<s>
At	O
the	O
acrimonious	O
review	O
meeting	O
by	O
the	O
company	O
's	O
Executive	O
Committee	O
in	O
July	O
1988	O
,	O
the	O
company	O
decided	O
to	O
cancel	O
Prism	O
,	O
and	O
continue	O
with	O
the	O
MIPS	O
workstations	B-Device
and	O
high-end	O
VAX	B-Device
products	O
.	O
</s>
<s>
The	O
workstation	B-Device
emerged	O
as	O
the	O
DECstation	B-Device
3100	I-Device
.	O
</s>
<s>
By	O
this	O
time	O
samples	O
of	O
the	O
microPRISM	B-Device
had	O
been	O
returned	O
and	O
were	O
found	O
to	O
be	O
mostly	O
working	O
.	O
</s>
<s>
They	O
also	O
proved	O
capable	O
of	O
running	O
at	O
speeds	O
of	O
50	O
to	O
80MHz	O
,	O
compared	O
to	O
the	O
R2000	B-Device
's	O
16	O
to	O
20	O
.	O
</s>
<s>
By	O
the	O
time	O
of	O
the	O
July	O
1988	O
meeting	O
,	O
the	O
company	O
had	O
swung	O
almost	O
entirely	O
into	O
the	O
position	O
that	O
the	O
RISC	B-Architecture
approach	O
was	O
a	O
workstation	B-Device
play	O
.	O
</s>
<s>
But	O
PRISM	O
's	O
performance	O
was	O
similar	O
to	O
that	O
of	O
the	O
latest	O
VAX	B-Device
machines	O
and	O
the	O
RISC	B-Architecture
concept	O
had	O
considerable	O
room	O
for	O
growth	O
.	O
</s>
<s>
As	O
the	O
meeting	O
broke	O
up	O
,	O
Ken	O
Olsen	O
asked	O
Supnik	O
to	O
investigate	O
ways	O
that	O
Digital	O
could	O
keep	O
the	O
performance	O
of	O
VMS	B-Operating_System
systems	O
competitive	O
with	O
RISC-based	B-Architecture
Unix	B-Application
systems	I-Application
.	O
</s>
<s>
A	O
group	O
of	O
engineers	O
formed	O
a	O
team	O
,	O
variously	O
referred	O
to	O
as	O
the	O
"	O
RISCy	O
VAX	B-Device
"	O
or	O
"	O
Extended	O
VAX	B-Device
"	O
(	O
EVAX	O
)	O
task	O
force	O
,	O
to	O
explore	O
this	O
issue	O
.	O
</s>
<s>
By	O
late	O
summer	O
,	O
the	O
group	O
had	O
explored	O
three	O
concepts	O
,	O
a	O
subset	O
of	O
the	O
VAX	B-Device
ISA	O
with	O
a	O
RISC-like	O
core	O
,	O
a	O
translated	O
VAX	B-Device
that	O
ran	O
native	O
VAX	B-Device
code	O
and	O
translated	O
it	O
on-the-fly	O
to	O
RISC	B-Architecture
code	O
and	O
stored	O
in	O
a	O
cache	O
,	O
and	O
the	O
ultrapipelined	O
VAX	B-Device
,	O
a	O
much	O
higher-performance	O
CISC	O
implementation	O
.	O
</s>
<s>
All	O
of	O
these	O
approaches	O
had	O
issues	O
that	O
meant	O
they	O
would	O
not	O
be	O
competitive	O
with	O
a	O
simple	O
RISC	B-Architecture
machine	O
.	O
</s>
<s>
The	O
group	O
next	O
considered	O
systems	O
that	O
combined	O
both	O
an	O
existing	O
VAX	B-Device
single-chip	O
solution	O
as	O
well	O
as	O
a	O
RISC	B-Architecture
chip	O
for	O
performance	O
needs	O
.	O
</s>
<s>
It	O
was	O
at	O
this	O
point	O
that	O
Nancy	O
Kronenberg	O
pointed	O
out	O
that	O
people	O
ran	O
VMS	B-Operating_System
,	O
not	O
VAX	B-Device
,	O
and	O
that	O
VMS	B-Operating_System
only	O
had	O
a	O
few	O
hardware	O
dependencies	O
based	O
on	O
its	O
modelling	O
of	O
interrupts	B-Application
and	O
memory	B-Architecture
paging	I-Architecture
.	O
</s>
<s>
There	O
appeared	O
to	O
be	O
no	O
compelling	O
reason	O
why	O
VMS	B-Operating_System
could	O
not	O
be	O
ported	O
to	O
a	O
RISC	B-Architecture
chip	O
as	O
long	O
as	O
these	O
small	O
bits	O
of	O
the	O
model	O
were	O
preserved	O
.	O
</s>
<s>
Two	O
questions	O
were	O
raised	O
:	O
could	O
the	O
resulting	O
RISC	B-Architecture
design	O
also	O
be	O
a	O
performance	O
leader	O
in	O
the	O
Unix	B-Application
market	O
,	O
and	O
should	O
the	O
machine	O
be	O
an	O
open	O
standard	O
?	O
</s>
<s>
And	O
with	O
that	O
,	O
the	O
decision	O
was	O
made	O
to	O
adopt	O
the	O
PRISM	O
architecture	O
with	O
the	O
appropriate	O
modifications	O
,	O
eventually	O
becoming	O
the	O
Alpha	B-Device
,	O
and	O
began	O
the	O
port	O
of	O
VMS	B-Operating_System
to	O
the	O
new	O
architecture	O
.	O
</s>
<s>
When	O
PRISM	O
and	O
MICA	B-Operating_System
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>
Cutler	O
's	O
architecture	O
for	O
NT	O
was	O
heavily	O
inspired	O
by	O
many	O
aspects	O
of	O
MICA	B-Operating_System
.	O
</s>
<s>
Of	O
the	O
32-bits	O
in	O
the	O
instructions	O
,	O
the	O
6	O
highest	O
and	O
5	O
lowest	O
bits	O
were	O
the	O
instruction	O
,	O
leaving	O
the	O
other	O
21	O
bits	O
of	O
the	O
word	O
for	O
encoding	O
either	O
a	O
constant	O
or	O
register	B-General_Concept
locations	O
.	O
</s>
<s>
PRISM	O
and	O
MIPS	O
both	O
lack	O
the	O
register	B-General_Concept
windows	I-General_Concept
that	O
were	O
a	O
hallmark	O
of	O
the	O
other	O
major	O
RISC	B-Architecture
design	O
,	O
Berkeley	B-General_Concept
RISC	I-General_Concept
.	O
</s>
<s>
The	O
PRISM	O
design	O
was	O
notable	O
for	O
several	O
aspects	O
of	O
its	O
instruction	B-General_Concept
set	I-General_Concept
.	O
</s>
<s>
Notably	O
,	O
PRISM	O
included	O
Epicode	O
(	O
extended	O
processor	O
instruction	O
code	O
)	O
,	O
which	O
defined	O
a	O
number	O
of	O
"	O
special	O
"	O
instructions	O
intended	O
to	O
offer	O
the	O
operating	B-General_Concept
system	I-General_Concept
a	O
stable	O
ABI	B-Operating_System
across	O
multiple	O
implementations	O
.	O
</s>
<s>
A	O
set	O
of	O
vector	B-Operating_System
processing	I-Operating_System
instructions	O
were	O
later	O
added	O
as	O
well	O
,	O
supported	O
by	O
an	O
additional	O
sixteen	O
64-bit	B-Device
vector	O
registers	O
that	O
could	O
be	O
used	O
in	O
a	O
variety	O
of	O
ways	O
.	O
</s>
