<s>
A	O
high-level	B-Architecture
language	I-Architecture
computer	I-Architecture
architecture	I-Architecture
(	O
HLLCA	B-Architecture
)	O
is	O
a	O
computer	B-General_Concept
architecture	I-General_Concept
designed	O
to	O
be	O
targeted	O
by	O
a	O
specific	O
high-level	B-Language
programming	I-Language
language	I-Language
(	O
HLL	O
)	O
,	O
rather	O
than	O
the	O
architecture	O
being	O
dictated	O
by	O
hardware	O
considerations	O
.	O
</s>
<s>
It	O
is	O
accordingly	O
also	O
termed	O
language-directed	O
computer	B-General_Concept
design	I-General_Concept
,	O
coined	O
in	O
and	O
primarily	O
used	O
in	O
the	O
1960s	O
and	O
1970s	O
.	O
</s>
<s>
HLLCAs	B-Architecture
were	O
popular	O
in	O
the	O
1960s	O
and	O
1970s	O
,	O
but	O
largely	O
disappeared	O
in	O
the	O
1980s	O
.	O
</s>
<s>
This	O
followed	O
the	O
dramatic	O
failure	O
of	O
the	O
Intel	B-Device
432	I-Device
(	O
1981	O
)	O
and	O
the	O
emergence	O
of	O
optimizing	B-Application
compilers	I-Application
and	O
reduced	B-Architecture
instruction	I-Architecture
set	I-Architecture
computer	I-Architecture
(	O
RISC	B-Architecture
)	O
architectures	O
and	O
RISC-like	O
complex	B-Architecture
instruction	I-Architecture
set	I-Architecture
computer	I-Architecture
(	O
CISC	O
)	O
architectures	O
,	O
and	O
the	O
later	O
development	O
of	O
just-in-time	O
compilation	B-Language
(	O
JIT	O
)	O
for	O
HLLs	O
.	O
</s>
<s>
HLLCAs	B-Architecture
date	O
almost	O
to	O
the	O
beginning	O
of	O
HLLs	O
,	O
in	O
the	O
Burroughs	B-Device
large	I-Device
systems	I-Device
(	O
1961	O
)	O
,	O
which	O
were	O
designed	O
for	O
ALGOL	B-Language
60	I-Language
(	O
1960	O
)	O
,	O
one	O
of	O
the	O
first	O
HLLs	O
.	O
</s>
<s>
The	O
best	O
known	O
HLLCAs	B-Architecture
may	O
be	O
the	O
Lisp	B-Operating_System
machines	I-Operating_System
of	O
the	O
1970s	O
and	O
1980s	O
,	O
for	O
the	O
language	O
Lisp	B-Language
(	O
1959	O
)	O
.	O
</s>
<s>
At	O
present	O
the	O
most	O
popular	O
HLLCAs	B-Architecture
are	O
Java	B-Language
processors	I-Language
,	O
for	O
the	O
language	O
Java	B-Language
(	O
1995	O
)	O
,	O
and	O
these	O
are	O
a	O
qualified	O
success	O
,	O
being	O
used	O
for	O
certain	O
applications	O
.	O
</s>
<s>
A	O
recent	O
architecture	O
in	O
this	O
vein	O
is	O
the	O
Heterogeneous	B-Architecture
System	I-Architecture
Architecture	I-Architecture
(	O
2012	O
)	O
,	O
which	O
HSA	O
Intermediate	O
Layer	O
(	O
HSAIL	O
)	O
provides	O
instruction	B-General_Concept
set	I-General_Concept
support	O
for	O
HLL	O
features	O
such	O
as	O
exceptions	O
and	O
virtual	O
functions	O
;	O
this	O
uses	O
JIT	O
to	O
ensure	O
performance	O
.	O
</s>
<s>
The	O
most	O
extreme	O
example	O
is	O
a	O
Directly	O
Executed	O
Language	O
,	O
where	O
the	O
instruction	B-General_Concept
set	I-General_Concept
architecture	I-General_Concept
(	O
ISA	O
)	O
of	O
the	O
computer	O
equals	O
the	O
instructions	O
of	O
the	O
HLL	O
,	O
and	O
the	O
source	O
code	O
is	O
directly	O
executable	O
with	O
minimal	O
processing	O
.	O
</s>
<s>
In	O
extreme	O
cases	O
,	O
the	O
only	O
compiling	B-Language
needed	O
is	O
tokenizing	O
the	O
source	O
code	O
and	O
feeding	O
the	O
tokens	O
directly	O
to	O
the	O
processor	O
;	O
this	O
is	O
found	O
in	O
stack-oriented	B-Language
programming	I-Language
languages	I-Language
running	O
on	O
a	O
stack	B-Application
machine	I-Application
.	O
</s>
<s>
In	O
less	O
extreme	O
examples	O
,	O
the	O
source	O
code	O
is	O
first	O
parsed	O
to	O
bytecode	O
,	O
which	O
is	O
then	O
the	O
machine	B-Language
code	I-Language
that	O
is	O
passed	O
to	O
the	O
processor	O
.	O
</s>
<s>
In	O
these	O
cases	O
,	O
the	O
system	O
typically	O
lacks	O
an	O
assembler	B-Language
,	O
as	O
the	O
compiler	B-Language
is	O
deemed	O
sufficient	O
,	O
though	O
in	O
some	O
cases	O
(	O
such	O
as	O
Java	B-Language
)	O
,	O
assemblers	B-Language
are	O
used	O
to	O
produce	O
legal	O
bytecode	O
which	O
would	O
not	O
be	O
output	O
by	O
the	O
compiler	B-Language
.	O
</s>
<s>
This	O
approach	O
was	O
found	O
in	O
the	O
Pascal	B-Device
MicroEngine	I-Device
(	O
1979	O
)	O
,	O
and	O
is	O
currently	O
used	O
by	O
Java	B-Language
processors	I-Language
.	O
</s>
<s>
More	O
loosely	O
,	O
a	O
HLLCA	B-Architecture
may	O
simply	O
be	O
a	O
general-purpose	O
computer	B-General_Concept
architecture	I-General_Concept
with	O
some	O
features	O
specifically	O
to	O
support	O
a	O
given	O
HLL	O
or	O
several	O
HLLs	O
.	O
</s>
<s>
This	O
was	O
found	O
in	O
Lisp	B-Operating_System
machines	I-Operating_System
from	O
the	O
1970s	O
onward	O
,	O
which	O
augmented	O
general-purpose	O
processors	O
with	O
operations	O
specifically	O
designed	O
to	O
support	O
Lisp	B-Language
.	O
</s>
<s>
The	O
Burroughs	B-Device
Large	I-Device
Systems	I-Device
(	O
1961	O
)	O
were	O
the	O
first	O
HLLCA	B-Architecture
,	O
designed	O
to	O
support	O
ALGOL	O
(	O
1959	O
)	O
,	O
one	O
of	O
the	O
earliest	O
HLLs	O
.	O
</s>
<s>
The	O
Burroughs	B-Language
Medium	I-Language
Systems	I-Language
(	O
1966	O
)	O
were	O
designed	O
to	O
support	O
COBOL	B-Application
for	O
business	O
applications	O
.	O
</s>
<s>
The	O
Burroughs	B-Device
Small	I-Device
Systems	I-Device
(	O
mid-1970s	O
,	O
designed	O
from	O
late	O
1960s	O
)	O
were	O
designed	O
to	O
support	O
multiple	O
HLLs	O
by	O
a	O
writable	O
control	B-General_Concept
store	I-General_Concept
.	O
</s>
<s>
The	O
Wang	B-Language
2200	I-Language
(	O
1973	O
)	O
series	O
were	O
designed	O
with	O
a	O
BASIC	O
interpreter	O
in	O
micro-code	B-Device
.	O
</s>
<s>
The	O
Pascal	B-Device
MicroEngine	I-Device
(	O
1979	O
)	O
was	O
designed	O
for	O
the	O
UCSD	B-Language
Pascal	I-Language
form	O
of	O
Pascal	B-Application
,	O
and	O
used	O
p-code	B-Language
(	O
Pascal	B-Application
compiler	B-Language
bytecode	O
)	O
as	O
its	O
machine	B-Language
code	I-Language
.	O
</s>
<s>
This	O
was	O
influential	O
on	O
the	O
later	O
development	O
of	O
Java	B-Language
and	O
Java	B-Language
machines	O
.	O
</s>
<s>
Lisp	B-Operating_System
machines	I-Operating_System
(	O
1970s	O
and	O
1980s	O
)	O
were	O
a	O
well-known	O
and	O
influential	O
group	O
of	O
HLLCAs	B-Architecture
.	O
</s>
<s>
Intel	B-Device
iAPX	I-Device
432	I-Device
(	O
1981	O
)	O
was	O
designed	O
to	O
support	O
Ada	O
.	O
</s>
<s>
Rekursiv	B-General_Concept
(	O
mid-1980s	O
)	O
was	O
a	O
minor	O
system	O
,	O
designed	O
to	O
support	O
object-oriented	B-Language
programming	I-Language
and	O
the	O
Lingo	O
programming	O
language	O
in	O
hardware	O
,	O
and	O
supported	O
recursion	O
at	O
the	O
instruction	B-General_Concept
set	I-General_Concept
level	O
,	O
hence	O
the	O
name	O
.	O
</s>
<s>
A	O
number	O
of	O
processors	O
and	O
coprocessors	O
intended	O
to	O
implement	O
Prolog	B-Language
more	O
directly	O
were	O
designed	O
in	O
the	O
late	O
1980s	O
and	O
early	O
1990s	O
,	O
including	O
the	O
,	O
its	O
successor	O
(	O
the	O
)	O
,	O
and	O
a	O
.	O
</s>
<s>
Like	O
Lisp	B-Language
,	O
Prolog	B-Language
's	O
basic	O
model	O
of	O
computation	O
is	O
radically	O
different	O
from	O
standard	O
imperative	O
designs	O
,	O
and	O
computer	O
scientists	O
and	O
electrical	O
engineers	O
were	O
eager	O
to	O
escape	O
the	O
bottlenecks	O
caused	O
by	O
emulating	O
their	O
underlying	O
models	O
.	O
</s>
<s>
Niklaus	O
Wirth	O
's	O
Lilith	B-Device
project	O
included	O
a	O
custom	O
CPU	O
geared	O
toward	O
the	O
Modula-2	B-Language
language	I-Language
.	O
</s>
<s>
The	O
INMOS	B-General_Concept
Transputer	I-General_Concept
was	O
designed	O
to	O
support	O
concurrent	O
programming	O
,	O
using	O
occam	B-Language
.	O
</s>
<s>
The	O
AT&T	B-Application
Hobbit	I-Application
processor	O
,	O
stemming	O
from	O
a	O
design	O
called	O
CRISP	O
(	O
C-language	B-Application
Reduced	I-Application
Instruction	I-Application
Set	I-Application
Processor	I-Application
)	O
,	O
was	O
optimized	O
to	O
run	O
C	B-Language
code	O
.	O
</s>
<s>
In	O
the	O
late	O
1990s	O
,	O
there	O
were	O
plans	O
by	O
Sun	O
Microsystems	O
and	O
other	O
companies	O
to	O
build	O
CPUs	O
that	O
directly	O
(	O
or	O
closely	O
)	O
implemented	O
the	O
stack-based	B-Language
Java	B-Language
virtual	I-Language
machine	I-Language
.	O
</s>
<s>
As	O
a	O
result	O
,	O
several	O
Java	B-Language
processors	I-Language
have	O
been	O
built	O
and	O
used	O
.	O
</s>
<s>
Ericsson	O
developed	O
ECOMP	O
,	O
a	O
processor	O
designed	O
to	O
run	O
Erlang	B-Operating_System
.	O
</s>
<s>
The	O
HSA	O
Intermediate	O
Layer	O
(	O
HSAIL	O
)	O
of	O
the	O
Heterogeneous	B-Architecture
System	I-Architecture
Architecture	I-Architecture
(	O
2012	O
)	O
provides	O
a	O
virtual	O
instruction	B-General_Concept
set	I-General_Concept
to	O
abstract	O
away	O
from	O
the	O
underlying	O
ISAs	O
,	O
and	O
has	O
support	O
for	O
HLL	O
features	O
such	O
as	O
exceptions	O
and	O
virtual	O
functions	O
,	O
and	O
include	O
debugging	O
support	O
.	O
</s>
<s>
HLLCA	B-Architecture
are	O
frequently	O
implemented	O
via	O
a	O
stack	B-Application
machine	I-Application
(	O
as	O
in	O
the	O
Burroughs	B-Device
Large	I-Device
Systems	I-Device
and	O
Intel	B-Device
432	I-Device
)	O
,	O
and	O
implemented	O
the	O
HLL	O
via	O
microcode	B-Device
in	O
the	O
processor	O
(	O
as	O
in	O
Burroughs	B-Device
Small	I-Device
Systems	I-Device
and	O
Pascal	B-Device
MicroEngine	I-Device
)	O
.	O
</s>
<s>
Tagged	B-Architecture
architectures	I-Architecture
are	O
frequently	O
used	O
to	O
support	O
types	O
(	O
as	O
in	O
the	O
Burroughs	B-Device
Large	I-Device
Systems	I-Device
and	O
Lisp	B-Operating_System
machines	I-Operating_System
)	O
.	O
</s>
<s>
More	O
radical	O
examples	O
use	O
a	O
non-von	B-Architecture
Neumann	I-Architecture
architecture	I-Architecture
,	O
though	O
these	O
are	O
typically	O
only	O
hypothetical	O
proposals	O
,	O
not	O
actual	O
implementations	O
.	O
</s>
<s>
Some	O
HLLCs	O
have	O
been	O
particularly	O
popular	O
as	O
developer	O
machines	O
(	O
workstations	O
)	O
,	O
due	O
to	O
fast	O
compiles	B-Language
and	O
low-level	O
control	O
of	O
the	O
system	O
with	O
a	O
high-level	B-Language
language	I-Language
.	O
</s>
<s>
Pascal	B-Device
MicroEngine	I-Device
and	O
Lisp	B-Operating_System
machines	I-Operating_System
are	O
good	O
examples	O
of	O
this	O
.	O
</s>
<s>
HLLCAs	B-Architecture
have	O
often	O
been	O
advocated	O
when	O
a	O
HLL	O
has	O
a	O
radically	O
different	O
model	O
of	O
computation	O
than	O
imperative	O
programming	O
(	O
which	O
is	O
a	O
relatively	O
good	O
match	O
for	O
typical	O
processors	O
)	O
,	O
notably	O
for	O
functional	O
programming	O
(	O
Lisp	B-Language
)	O
and	O
logic	O
programming	O
(	O
Prolog	B-Language
)	O
.	O
</s>
<s>
HLLCAs	B-Architecture
are	O
intuitively	O
appealing	O
,	O
as	O
the	O
computer	O
can	O
in	O
principle	O
be	O
customized	O
for	O
a	O
language	O
,	O
allowing	O
optimal	O
support	O
for	O
the	O
language	O
,	O
and	O
simplifying	O
compiler	B-Language
writing	O
.	O
</s>
<s>
It	O
can	O
further	O
natively	O
support	O
multiple	O
languages	O
by	O
simply	O
changing	O
the	O
microcode	B-Device
.	O
</s>
<s>
Key	O
advantages	O
are	O
to	O
developers	O
:	O
fast	O
compilation	B-Language
and	O
detailed	O
symbolic	O
debugging	O
from	O
the	O
machine	O
.	O
</s>
<s>
A	O
further	O
advantage	O
is	O
that	O
a	O
language	O
implementation	O
can	O
be	O
updated	O
by	O
updating	O
the	O
microcode	B-Device
(	O
firmware	B-Application
)	O
,	O
without	O
requiring	O
recompilation	O
of	O
an	O
entire	O
system	O
.	O
</s>
<s>
The	O
software	O
those	O
depend	O
on	O
,	O
from	O
OS	O
to	O
virtual	O
machines	O
,	O
leverage	O
native	B-Language
code	I-Language
with	O
no	O
protection	O
.	O
</s>
<s>
One	O
solution	O
is	O
to	O
use	O
a	O
processor	O
custom	O
built	O
to	O
execute	O
a	O
safe	O
high	B-Language
level	I-Language
language	I-Language
or	O
at	O
least	O
understand	O
types	O
.	O
</s>
<s>
Compare	O
language-based	B-Operating_System
systems	I-Operating_System
,	O
where	O
the	O
software	O
(	O
especially	O
operating	O
system	O
)	O
is	O
based	O
around	O
a	O
safe	O
,	O
high-level	B-Language
language	I-Language
,	O
though	O
the	O
hardware	O
need	O
not	O
be	O
:	O
the	O
"	O
trusted	O
base	O
"	O
may	O
still	O
be	O
in	O
a	O
lower	O
level	O
language	O
.	O
</s>
<s>
The	O
simplest	O
reason	O
for	O
the	O
lack	O
of	O
success	O
of	O
HLLCAs	B-Architecture
is	O
that	O
from	O
1980	O
optimizing	B-Application
compilers	I-Application
resulted	O
in	O
much	O
faster	O
code	O
and	O
were	O
easier	O
to	O
develop	O
than	O
implementing	O
a	O
language	O
in	O
microcode	B-Device
.	O
</s>
<s>
Many	O
compiler	B-Application
optimizations	I-Application
require	O
complex	O
analysis	O
and	O
rearrangement	O
of	O
the	O
code	O
,	O
so	O
the	O
machine	B-Language
code	I-Language
is	O
very	O
different	O
from	O
the	O
original	O
source	O
code	O
.	O
</s>
<s>
These	O
optimizations	O
are	O
either	O
impossible	O
or	O
impractical	O
to	O
implement	O
in	O
microcode	B-Device
,	O
due	O
to	O
the	O
complexity	O
and	O
the	O
overhead	O
.	O
</s>
<s>
Analogous	O
performance	O
problems	O
have	O
a	O
long	O
history	O
with	O
interpreted	O
languages	O
(	O
dating	O
to	O
Lisp	B-Language
(	O
1958	O
)	O
)	O
,	O
only	O
being	O
resolved	O
adequately	O
for	O
practical	O
use	O
by	O
just-in-time	O
compilation	B-Language
,	O
pioneered	O
in	O
Self	B-Operating_System
and	O
commercialized	O
in	O
the	O
HotSpot	B-Language
Java	B-Language
virtual	I-Language
machine	I-Language
(	O
1999	O
)	O
.	O
</s>
<s>
The	O
fundamental	O
problem	O
is	O
that	O
HLLCAs	B-Architecture
only	O
simplify	O
the	O
code	B-Application
generation	I-Application
step	O
of	O
compilers	B-Language
,	O
which	O
is	O
typically	O
a	O
relatively	O
small	O
part	O
of	O
compilation	B-Language
,	O
and	O
a	O
questionable	O
use	O
of	O
computing	O
power	O
(	O
transistors	O
and	O
microcode	B-Device
)	O
.	O
</s>
<s>
A	O
deeper	O
problem	O
,	O
still	O
an	O
active	O
area	O
of	O
development	O
,	O
is	O
that	O
providing	O
HLL	O
debugging	O
information	O
from	O
machine	B-Language
code	I-Language
is	O
quite	O
difficult	O
,	O
basically	O
because	O
of	O
the	O
overhead	O
of	O
debugging	O
information	O
,	O
and	O
more	O
subtly	O
because	O
compilation	B-Language
(	O
particularly	O
optimization	O
)	O
makes	O
determining	O
the	O
original	O
source	O
for	O
a	O
machine	B-Language
instruction	I-Language
quite	O
involved	O
.	O
</s>
<s>
Thus	O
the	O
debugging	O
information	O
provided	O
as	O
an	O
essential	O
part	O
of	O
HLLCAs	B-Architecture
either	O
severely	O
limits	O
implementation	O
or	O
adds	O
significant	O
overhead	O
in	O
ordinary	O
use	O
.	O
</s>
<s>
Further	O
,	O
HLLCAs	B-Architecture
are	O
typically	O
optimized	O
for	O
one	O
language	O
,	O
supporting	O
other	O
languages	O
more	O
poorly	O
.	O
</s>
<s>
Similar	O
issues	O
arise	O
in	O
multi-language	O
virtual	O
machines	O
,	O
notably	O
the	O
Java	B-Language
virtual	I-Language
machine	I-Language
(	O
designed	O
for	O
Java	B-Language
)	O
and	O
the	O
.NET	O
Common	O
Language	O
Runtime	O
(	O
designed	O
for	O
C#	B-Application
)	O
,	O
where	O
other	O
languages	O
are	O
second-class	O
citizens	O
,	O
and	O
often	O
must	O
hew	O
closely	O
to	O
the	O
main	O
language	O
in	O
semantics	O
.	O
</s>
<s>
For	O
this	O
reason	O
lower-level	O
ISAs	O
allow	O
multiple	O
languages	O
to	O
be	O
well-supported	O
,	O
given	O
compiler	B-Language
support	O
.	O
</s>
<s>
However	O
,	O
a	O
similar	O
issue	O
arises	O
even	O
for	O
many	O
apparently	O
language-neutral	O
processors	O
,	O
which	O
are	O
well-supported	O
by	O
the	O
language	O
C	B-Language
,	O
and	O
where	O
transpiling	B-Language
to	O
C	B-Language
(	O
rather	O
than	O
directly	O
targeting	O
the	O
hardware	O
)	O
yields	O
efficient	O
programs	O
and	O
simple	O
compilers	B-Language
.	O
</s>
<s>
The	O
advantages	O
of	O
HLLCAs	B-Architecture
can	O
be	O
alternatively	O
achieved	O
in	O
HLL	O
Computer	O
Systems	O
(	O
language-based	B-Operating_System
systems	I-Operating_System
)	O
in	O
alternative	O
ways	O
,	O
primarily	O
via	O
compilers	B-Language
or	O
interpreters	O
:	O
the	O
system	O
is	O
still	O
written	O
in	O
a	O
HLL	O
,	O
but	O
there	O
is	O
a	O
trusted	O
base	O
in	O
software	O
running	O
on	O
a	O
lower-level	O
architecture	O
.	O
</s>
<s>
This	O
has	O
been	O
the	O
approach	O
followed	O
since	O
circa	O
1980	O
:	O
for	O
example	O
,	O
a	O
Java	B-Language
system	O
where	O
the	O
runtime	O
environment	O
itself	O
is	O
written	O
in	O
C	B-Language
,	O
but	O
the	O
operating	O
system	O
and	O
applications	O
written	O
in	O
Java	B-Language
.	O
</s>
<s>
Since	O
the	O
1980s	O
the	O
focus	O
of	O
research	O
and	O
implementation	O
in	O
general-purpose	O
computer	B-General_Concept
architectures	I-General_Concept
has	O
primarily	O
been	O
in	O
RISC-like	O
architectures	O
,	O
typically	O
internally	O
register-rich	O
load	B-Architecture
–	I-Architecture
store	I-Architecture
architectures	I-Architecture
,	O
with	O
rather	O
stable	O
,	O
non-language-specific	O
ISAs	O
,	O
featuring	O
multiple	O
registers	O
,	O
pipelining	O
,	O
and	O
more	O
recently	O
multicore	O
systems	O
,	O
rather	O
than	O
language-specific	O
ISAs	O
.	O
</s>
<s>
Language	O
support	O
has	O
focused	O
on	O
compilers	B-Language
and	O
their	O
runtimes	O
,	O
and	O
interpreters	O
and	O
their	O
virtual	O
machines	O
(	O
particularly	O
JIT'ing	O
ones	O
)	O
,	O
with	O
little	O
direct	O
hardware	O
support	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
current	O
Objective-C	B-Language
runtime	O
for	O
iOS	O
implements	O
tagged	O
pointers	O
,	O
which	O
it	O
uses	O
for	O
type-checking	O
and	O
garbage	O
collection	O
,	O
despite	O
the	O
hardware	O
not	O
being	O
a	O
tagged	B-Architecture
architecture	I-Architecture
.	O
</s>
<s>
In	O
computer	B-General_Concept
architecture	I-General_Concept
,	O
the	O
RISC	B-Architecture
approach	O
has	O
proven	O
very	O
popular	O
and	O
successful	O
instead	O
,	O
and	O
is	O
opposite	O
from	O
HLLCAs	B-Architecture
,	O
emphasizing	O
a	O
very	O
simple	O
instruction	B-General_Concept
set	I-General_Concept
architecture	I-General_Concept
.	O
</s>
<s>
However	O
,	O
the	O
speed	O
advantages	O
of	O
RISC	B-Architecture
computers	O
in	O
the	O
1980s	O
was	O
primarily	O
due	O
to	O
early	O
adoption	O
of	O
on-chip	B-General_Concept
cache	I-General_Concept
and	O
room	O
for	O
large	O
registers	O
,	O
rather	O
than	O
intrinsic	O
advantages	O
of	O
RISC	B-Architecture
..	O
</s>
