<s>
The	O
Jupiter	B-Language
Ace	I-Language
by	O
Jupiter	O
Cantab	O
was	O
a	O
British	O
home	O
computer	O
of	O
the	O
early	O
1980s	O
.	O
</s>
<s>
The	O
Ace	O
differed	O
from	O
other	O
microcomputers	O
of	O
the	O
time	O
in	O
that	O
its	O
programming	O
environment	O
used	O
Forth	B-Application
instead	O
of	O
the	O
more	O
popular	O
BASIC	O
.	O
</s>
<s>
The	O
Jupiter	B-Language
Ace	I-Language
was	O
a	O
small	O
computer	O
system	O
developed	O
by	O
Jupiter	O
Cantab	O
,	O
founded	O
by	O
Richard	O
Altwasser	O
and	O
Steven	O
Vickers	O
,	O
both	O
of	O
whom	O
had	O
worked	O
on	O
the	O
ZX	B-Operating_System
Spectrum	I-Operating_System
.	O
</s>
<s>
Named	O
after	O
the	O
early	O
British	O
computer	O
,	O
the	O
Pilot	B-Device
ACE	I-Device
,	O
the	O
Jupiter	B-Language
Ace	I-Language
utilized	O
the	O
Forth	B-Application
programming	I-Application
language	I-Application
instead	O
of	O
the	O
more	O
common	O
BASIC	O
.	O
</s>
<s>
The	O
machine	O
struggled	O
to	O
gain	O
acceptance	O
due	O
to	O
its	O
use	O
of	O
Forth	B-Application
,	O
limited	O
published	O
software	O
,	O
poor	O
case	O
design	O
,	O
and	O
small	O
initial	O
memory	B-Architecture
.	O
</s>
<s>
Additionally	O
,	O
its	O
tile-based	O
monochrome	O
graphics	O
were	O
inferior	O
to	O
competing	O
machines	O
 '	O
pixel-based	O
color	O
graphics	O
.	O
</s>
<s>
The	O
Jupiter	B-Language
Ace	I-Language
was	O
similar	O
in	O
size	O
,	O
cost	O
,	O
and	O
form	O
factor	O
to	O
the	O
ZX81	O
,	O
but	O
had	O
a	O
design	O
more	O
akin	O
to	O
the	O
ZX	B-Operating_System
Spectrum	I-Operating_System
.	O
</s>
<s>
It	O
used	O
a	O
Zilog	B-General_Concept
Z80	I-General_Concept
processor	O
and	O
featured	O
an	O
8	O
KB	O
ROM	B-Device
and	O
1	O
KB	O
of	O
user	O
RAM	B-Architecture
.	O
</s>
<s>
Its	O
character	B-General_Concept
set	I-General_Concept
was	O
based	O
on	O
ASCII-1967	O
with	O
extensions	O
,	O
and	O
it	O
included	O
a	O
40-key	O
QWERTY	O
keyboard	B-Device
.	O
</s>
<s>
The	O
Jupiter	B-Language
Ace	I-Language
used	O
the	O
Forth	B-Application
programming	I-Application
language	I-Application
,	O
a	O
structured	O
language	O
that	O
ran	O
nearly	O
as	O
fast	O
as	O
many	O
native-compiled	O
languages	O
.	O
</s>
<s>
The	O
choice	O
of	O
Forth	B-Application
allowed	O
for	O
memory-efficient	O
programs	O
and	O
complex	O
program	O
implementation	O
,	O
while	O
using	O
less	O
memory	B-Architecture
compared	O
to	O
programs	O
written	O
in	O
interpreted	O
BASIC	O
.	O
</s>
<s>
The	O
Ace	O
's	O
Forth	B-Application
was	O
based	O
on	O
Forth-79	O
and	O
featured	O
added	O
syntax	O
checking	O
and	O
extra	O
words	O
based	O
on	O
common	O
BASIC	O
sound	O
,	O
video	O
,	O
and	O
tape	O
commands	O
.	O
</s>
<s>
The	O
Jupiter	B-Language
Ace	I-Language
was	O
compatible	O
with	O
some	O
ZX-81	O
add-ons	O
and	O
had	O
several	O
peripherals	O
and	O
interfaces	O
available	O
,	O
including	O
RAM	B-Architecture
packs	O
,	O
a	O
keyboard	B-Device
,	O
sound	O
,	O
storage	O
,	O
printer	O
adapters	O
,	O
and	O
a	O
graphics	O
card	O
.	O
</s>
<s>
The	O
original	O
Jupiter	B-Language
Ace	I-Language
was	O
produced	O
in	O
1982	O
,	O
followed	O
by	O
the	O
Jupiter	B-Language
Ace	I-Language
4000	O
in	O
1983	O
.	O
</s>
<s>
Both	O
had	O
been	O
on	O
the	O
design	O
team	O
for	O
the	O
ZX	B-Operating_System
Spectrum	I-Operating_System
:	O
Altwasser	O
did	O
some	O
work	O
on	O
the	O
development	O
of	O
the	O
ZX-81	O
and	O
in	O
the	O
design	O
of	O
the	O
hardware	O
of	O
the	O
Spectrum	O
.	O
</s>
<s>
Vickers	O
adapted	O
and	O
expanded	O
the	O
4K	O
ZX-80	O
ROM	B-Device
to	O
the	O
8K	O
ZX-81	O
ROM	B-Device
and	O
wrote	O
most	O
of	O
the	O
ROM	B-Device
for	O
the	O
Spectrum	O
.	O
</s>
<s>
The	O
Jupiter	B-Language
Ace	I-Language
was	O
named	O
after	O
an	O
early	O
British	O
computer	O
,	O
the	O
Pilot	B-Device
ACE	I-Device
.	O
</s>
<s>
The	O
use	O
of	O
Forth	B-Application
rather	O
than	O
the	O
more	O
usual	O
choice	O
of	O
BASIC	O
,	O
and	O
the	O
availability	O
and	O
success	O
of	O
the	O
ZX	B-Operating_System
Spectrum	I-Operating_System
,	O
as	O
well	O
as	O
limited	O
published	O
software	O
,	O
the	O
poor	O
case	O
and	O
small	O
initial	O
memory	B-Architecture
all	O
weighed	O
against	O
wider	O
market	O
acceptance	O
.	O
</s>
<s>
Forth	B-Application
,	O
while	O
being	O
structured	O
and	O
powerful	O
,	O
was	O
considered	O
difficult	O
to	O
learn	O
,	O
and	O
a	O
knowledge	O
of	O
BASIC	O
acquired	O
from	O
familiarity	O
with	O
other	O
home	O
computers	O
was	O
of	O
no	O
practical	O
help	O
in	O
learning	O
it	O
.	O
</s>
<s>
A	O
1982	O
review	O
stated	O
that	O
"	O
The	O
success	O
of	O
the	O
Jupiter	B-Language
Ace	I-Language
will	O
depend	O
on	O
the	O
machine-buying	O
public	O
's	O
acceptance	O
of	O
another	O
microcomputer	O
language.	O
"	O
</s>
<s>
Further	O
,	O
there	O
was	O
only	O
a	O
very	O
limited	O
range	O
of	O
published	O
software	O
-	O
either	O
commercial	O
programs	O
or	O
type-in	O
programs	O
printed	O
in	O
hobby	O
magazines	O
-	O
for	O
the	O
machine	O
,	O
and	O
these	O
were	O
restricted	O
by	O
the	O
base	O
model	O
's	O
small	O
amount	O
of	O
RAM	B-Architecture
.	O
</s>
<s>
Attempts	O
to	O
promote	O
the	O
Ace	O
in	O
the	O
educational	O
market	O
also	O
failed	O
;	O
doubts	O
over	O
whether	O
Forth	B-Application
would	O
be	O
relevant	O
for	O
exam	O
syllabuses	O
,	O
and	O
the	O
lack	O
of	O
support	O
for	O
Forth	B-Application
from	O
teaching	O
staff	O
were	O
key	O
issues	O
.	O
</s>
<s>
Finally	O
,	O
the	O
tile-based	O
graphics	O
compared	O
poorly	O
to	O
the	O
pixel-based	O
graphics	O
of	O
other	O
machines	O
-	O
which	O
were	O
also	O
colour	O
rather	O
than	O
the	O
Ace	O
's	O
monochrome	O
.	O
</s>
<s>
The	O
Jupiter	B-Language
Ace	I-Language
is	O
often	O
compared	O
with	O
ZX81	O
due	O
to	O
its	O
similar	O
size	O
,	O
low	O
cost	O
,	O
and	O
similar	O
form	O
factor	O
.	O
</s>
<s>
Internally	O
its	O
design	O
is	O
more	O
similar	O
to	O
the	O
ZX	B-Operating_System
Spectrum	I-Operating_System
although	O
the	O
Ace	O
also	O
had	O
a	O
dedicated	O
video	O
memory	B-Architecture
of	O
2	O
KB	O
,	O
partly	O
avoiding	O
the	O
slow	O
down	O
when	O
programs	O
accessed	O
the	O
same	O
bank	O
(	O
same	O
chips	O
)	O
as	O
the	O
video	O
memory	B-Architecture
.	O
</s>
<s>
Like	O
the	O
Spectrum	O
,	O
the	O
Ace	O
used	O
black	O
conductive	O
rubber	B-Device
keys	I-Device
.	O
</s>
<s>
The	O
Jupiter	B-Language
Ace	I-Language
was	O
based	O
on	O
the	O
Zilog	B-General_Concept
Z80	I-General_Concept
,	O
which	O
the	O
designers	O
had	O
previous	O
experience	O
of	O
from	O
working	O
on	O
the	O
Sinclair	O
ZX81	O
and	O
ZX	B-Operating_System
Spectrum	I-Operating_System
.	O
</s>
<s>
Both	O
graphics	O
and	O
text	O
could	O
be	O
displayed	O
at	O
the	O
same	O
time	O
:	O
(	O
1	O
)	O
redefinition	O
of	O
the	O
character	O
tiles	B-Application
provided	O
standard	O
256×192	O
graphics	O
limited	O
to	O
the	O
128	O
available	O
(	O
definable	O
)	O
8×8	O
chars	O
,	O
concurrent	B-Operating_System
with	O
plotting	O
of	O
64×48	O
graphics	O
.	O
</s>
<s>
Files	O
could	O
be	O
used	O
for	O
either	O
storage	O
of	O
Forth	B-Application
programs	O
(	O
compiled	O
code	O
)	O
or	O
raw	O
dumps	O
of	O
memory	B-Architecture
.	O
</s>
<s>
The	O
Ace	O
had	O
an	O
8	O
KB	O
ROM	B-Device
containing	O
the	O
Forth	B-Application
kernel	B-Operating_System
and	O
operating	B-General_Concept
system	I-General_Concept
,	O
and	O
the	O
predefined	O
dictionary	O
of	O
Forth	B-Application
words	O
in	O
about	O
5	O
KB	O
.	O
</s>
<s>
The	O
remaining	O
3	O
KB	O
of	O
ROM	B-Device
supported	O
several	O
functionalities	O
:	O
floating	B-Algorithm
point	I-Algorithm
numbers	I-Algorithm
library	O
and	O
character	O
definitions	O
table	O
,	O
tape	O
recorder	O
access	O
,	O
decompiling	O
and	O
redefining	O
newly	O
re-edited	O
'	O
words	O
 '	O
(	O
i.e.	O
</s>
<s>
Some	O
of	O
the	O
ROM	B-Device
was	O
written	O
in	O
Z80	B-General_Concept
machine	B-Language
code	I-Language
,	O
but	O
some	O
was	O
also	O
coded	O
in	O
Forth	B-Application
.	O
</s>
<s>
The	O
next	O
8	O
KB	O
was	O
built	O
in	O
RAM	B-Architecture
that	O
was	O
only	O
partially	O
decoded	B-Device
,	O
with	O
2	O
KB	O
of	O
video	O
RAM	B-Architecture
echoed	O
twice	O
,	O
and	O
1	O
KB	O
of	O
user	O
RAM	B-Architecture
echoed	O
4	O
times	O
(	O
with	O
the	O
same	O
memory	B-Architecture
appearing	O
at	O
several	O
different	O
memory	B-Architecture
addresses	O
)	O
.	O
</s>
<s>
Using	O
the	O
lower-address	O
mirror	O
of	O
the	O
video	O
RAM	B-Architecture
would	O
select	O
CPU	O
priority	O
,	O
resulting	O
in	O
some	O
momentary	O
random	O
pixels	B-Algorithm
on	O
the	O
screen	O
when	O
video	O
subsystem	O
and	O
the	O
CPU	O
accessed	O
the	O
video	O
RAM	B-Architecture
in	O
the	O
same	O
clock	O
cycle	O
.	O
</s>
<s>
Since	O
video	O
RAM	B-Architecture
was	O
partially	O
separated	O
from	O
the	O
main	O
address	O
and	O
data	O
busses	O
,	O
for	O
the	O
most	O
part	O
the	O
video	O
subsystem	O
and	O
the	O
CPU	O
could	O
operate	O
in	B-Operating_System
parallel	I-Operating_System
.	O
</s>
<s>
The	O
first	O
16	O
KB	O
of	O
the	O
memory	B-Architecture
map	O
was	O
used	O
for	O
ROM	B-Device
,	O
Video	O
and	O
User-available	O
RAM	B-Architecture
,	O
leaving	O
the	O
second	O
16	O
KB	O
of	O
the	O
memory	B-Architecture
map	O
free	O
for	O
RAM	B-Architecture
extension	O
and	O
the	O
topmost	O
32	O
KB	O
undefined	O
.	O
</s>
<s>
One	O
1K	O
bank	O
allowed	O
redefinition	O
of	O
most	O
of	O
its	O
128	O
ASCII-based	O
characters	O
in	O
8×8	O
pixel	B-Algorithm
bitmap	O
format	O
.	O
</s>
<s>
1	O
KB	O
RAM	B-Architecture
with	O
the	O
option	O
of	O
a	O
16	O
KB	O
RAM-Pack	O
,	O
and	O
later	O
a	O
32	O
KB	O
one	O
.	O
</s>
<s>
A	O
PCB	O
was	O
also	O
marketed	O
by	O
Boldfield	O
Computing	O
that	O
converted	O
the	O
edge	O
connector	O
to	O
electrical	O
compatibility	O
with	O
a	O
Sinclair	O
ZX81	O
,	O
allowing	O
use	O
of	O
the	O
ZX81	O
16K	O
RAM	B-Architecture
pack	O
.	O
</s>
<s>
Characteristic	O
Value	O
Processor	O
Zilog	B-General_Concept
Z80A	I-General_Concept
clocked	O
at	O
3.25	O
MHz	O
.	O
</s>
<s>
Operating	B-General_Concept
System	I-General_Concept
FORTH	B-Application
(	O
as	O
both	O
Programming	O
language	O
and	O
Command-line	B-Application
interface	I-Application
)	O
.	O
</s>
<s>
Memory	B-Architecture
2KB	O
for	O
Video	O
+	O
1	O
KB	O
base	O
expandable	O
up	O
to	O
49	O
KB	O
(	O
Video	O
excluded	O
)	O
.	O
</s>
<s>
Video	O
Independent	O
sub-system	O
with	O
2	O
dedicated	O
SRAM	B-Architecture
banks	O
:	O
Screen	O
(	O
1	O
KB	O
)	O
+	O
Char	O
Tiles	B-Application
(	O
1	O
KB	O
)	O
.	O
</s>
<s>
Keyboard	B-Device
and	O
Charset	B-General_Concept
40	O
keys	O
Qwerty	O
Keyboard	B-Device
(	O
Symbols	O
access	O
with	O
extra	O
key	O
)	O
.	O
</s>
<s>
All	O
chars	O
in	O
Charset	B-General_Concept
(	O
based	O
on	O
ASCII-1967	O
)	O
being	O
redefinable	O
.	O
</s>
<s>
Character	B-General_Concept
set	I-General_Concept
Based	O
on	O
ASCII-1967	O
with	O
extensions	O
as	O
for	O
the	O
ZX	B-Operating_System
Spectrum	I-Operating_System
character	B-General_Concept
set	I-General_Concept
including	O
↑	O
,	O
£	O
and	O
©	O
.	O
</s>
<s>
References	O
to	O
the	O
Ace	O
RAM	B-Architecture
sometimes	O
include	O
the	O
separate	O
2	O
KB	O
video	O
memory	B-Architecture
,	O
which	O
was	O
not	O
available	O
for	O
programming	O
,	O
thus	O
leading	O
to	O
some	O
confusion	O
.	O
</s>
<s>
Similarly	O
,	O
it	O
is	O
sometimes	O
argued	O
that	O
because	O
of	O
Forth	B-Application
's	O
efficiency	O
,	O
the	O
1KB	O
standard	O
RAM	B-Architecture
was	O
in	O
effect	O
comparable	O
to	O
at	O
least	O
2KB	O
on	O
a	O
BASIC	O
system	O
.	O
</s>
<s>
Its	O
most	O
distinctive	O
characteristic	O
was	O
the	O
choice	O
of	O
Forth	B-Application
,	O
a	O
structured	O
language	O
.	O
</s>
<s>
Forth	B-Application
was	O
considered	O
well	O
adapted	O
to	O
microcomputers	O
with	O
their	O
small	O
memory	B-Architecture
and	O
relatively	O
low-performance	O
processors	O
.	O
</s>
<s>
Forth	B-Application
programs	O
are	O
memory-efficient	O
;	O
as	O
they	O
become	O
bigger	O
,	O
they	O
reuse	O
more	O
previously-defined	O
code	O
.	O
</s>
<s>
Control	O
structures	O
could	O
be	O
nested	O
to	O
any	O
level	O
,	O
limited	O
only	O
by	O
available	O
memory	B-Architecture
.	O
</s>
<s>
The	O
Ace	O
's	O
Forth	B-Application
was	O
stated	O
to	O
be	O
"	O
ten	O
times	O
faster	O
than	O
Basic	O
"	O
and	O
used	O
less	O
than	O
half	O
the	O
memory	B-Architecture
(	O
a	O
significant	O
cost	O
percentage	O
of	O
low	O
end	O
computers	O
of	O
the	O
time	O
)	O
of	O
an	O
equivalent	O
program	O
written	O
in	O
interpreted	O
BASIC	O
.	O
</s>
<s>
It	O
also	O
allowed	O
easy	O
implementation	O
of	O
machine	B-Language
code	I-Language
routines	O
if	O
needed	O
.	O
</s>
<s>
Ace	O
's	O
Forth	B-Application
was	O
based	O
mostly	O
on	O
Forth-79	O
,	O
with	O
some	O
relevant	O
differences	O
,	O
in	O
particular	O
it	O
added	O
syntax	O
checking	O
to	O
control	O
structures	O
and	O
definer	O
constructions	O
and	O
a	O
few	O
extra	O
words	O
were	O
added	O
based	O
on	O
common	O
BASIC	O
sound	O
,	O
video	O
and	O
tape	O
commands	O
.	O
</s>
<s>
The	O
implementation	O
lacked	O
some	O
less	O
frequently	O
used	O
Forth	B-Application
words	O
,	O
these	O
being	O
easily	O
implemented	O
if	O
needed	O
.	O
</s>
<s>
Runtime	B-Library
error	I-Library
checking	O
could	O
be	O
turned	O
off	O
to	O
raise	O
speed	O
by	O
25%	O
to	O
50%	O
.	O
</s>
<s>
Its	O
Forth	B-Application
was	O
adapted	O
to	O
the	O
disk-less	O
tape-using	O
home	O
computer	O
hardware	O
by	O
being	O
able	O
to	O
save/load	O
user	O
"	O
compiled	O
vocabularies	O
"	O
,	O
instead	O
of	O
the	O
usual	O
numbered	O
programming	O
blocks	O
used	O
by	O
diskette	O
systems	O
.	O
</s>
<s>
Decompiling	O
avoided	O
wasting	O
RAM	B-Architecture
in	O
simulating	O
an	O
absent	O
Block	O
System	O
,	O
used	O
with	O
both	O
disk	O
and	O
tape	O
drivers	O
(	O
these	O
last	O
not	O
to	O
be	O
confused	O
with	O
tape	O
recorders	O
)	O
.	O
</s>
<s>
These	O
solutions	O
were	O
unique	O
to	O
the	O
Jupiter	B-Language
Ace	I-Language
.	O
</s>
<s>
To	O
allow	O
decompile	O
,	O
it	O
distinguished	O
usual	O
Forth	B-Application
definer	O
and	O
compiler	O
words	O
creation	O
,	O
replacing	O
the	O
CREATE	O
..	O
DOES>	O
,	O
creation	O
pair	O
with	O
:	O
</s>
<s>
Similar	O
to	O
CREATE	O
..	O
DOES	O
usage	O
in	O
standard	O
FORTH	B-Application
.	O
</s>
<s>
COMPILER	O
..	O
RUNS>	O
:	O
Create	O
new	O
Compiling	O
words	O
,	O
less	O
frequently	O
used	O
to	O
extend	O
the	O
language	O
with	O
compiler	O
words	O
where	O
CREATE	O
..	O
DOES	O
is	O
FORTH	B-Application
implementation	O
dependent	O
.	O
</s>
<s>
These	O
2	O
defining	O
pairs	O
,	O
instead	O
of	O
one	O
alone	O
,	O
allowed	O
the	O
Ace	O
to	O
decompile	O
its	O
programs	O
,	O
unlike	O
usual	O
Forth	B-Application
systems	O
.	O
</s>
<s>
This	O
decompiling	O
ability	O
was	O
a	O
solution	O
to	O
the	O
absence	O
of	O
the	O
more	O
flexible	O
disk	O
system	O
used	O
by	O
Forth	B-Application
.	O
</s>
<s>
Not	O
storing	O
the	O
source	O
of	O
a	O
Forth	B-Application
program	O
,	O
but	O
compiling	O
the	O
code	O
after	O
editing	O
,	O
it	O
avoided	O
completely	O
the	O
emulation	O
of	O
a	O
disk/tape	O
drive	O
on	O
RAM	B-Architecture
saving	O
computer	B-General_Concept
memory	I-General_Concept
.	O
</s>
<s>
This	O
tape-friendly	O
and	O
RAM-saving	O
solution	O
was	O
unique	O
to	O
the	O
Jupiter	B-Language
Ace	I-Language
Forth	B-Application
.	O
</s>
<s>
The	O
names	O
can	O
be	O
equivocal	O
out	O
of	O
a	O
Forth	B-Application
context	O
,	O
as	O
all	O
Words	O
are	O
compiled	O
when	O
declared	O
.	O
</s>
<s>
These	O
'	O
Structured	O
Programming	O
 '	O
are	O
active	O
on	O
'	O
Compile	O
 '	O
mode	O
(	O
which	O
is	O
simply	O
building	O
a	O
new	O
Forth	B-Application
Word	O
)	O
.	O
</s>
<s>
Although	O
not	O
explicitly	O
designed	O
for	O
such	O
a	O
purpose	O
,	O
the	O
compiled	O
Forth	B-Application
could	O
be	O
utilised	O
for	O
ROM	B-Device
extensions	O
to	O
the	O
built	O
in	O
system	O
.	O
</s>
<s>
External	O
ROMs	O
were	O
developed	O
with	O
Ace	O
Forth	B-Application
to	O
be	O
used	O
as	O
control	O
applications	O
.	O
</s>
<s>
The	O
machine	O
was	O
able	O
to	O
use	O
some	O
ZX-81	O
add-ons	O
due	O
to	O
similar	O
RAM	B-Architecture
locations	O
,	O
and	O
external	O
expansion	O
slot	O
.	O
</s>
<s>
Jupiter	O
Cantab	O
made	O
a	O
16	O
KB	O
RAM	B-Architecture
pack	O
,	O
and	O
external	O
companies	O
made	O
similar	O
RAM	B-Architecture
packs	O
as	O
well	O
as	O
other	O
peripherals	O
and	O
interfaces	O
.	O
</s>
<s>
48	O
KB	O
by	O
Boldfield	O
(	O
new	O
Jupiter	B-Language
Ace	I-Language
owner	O
after	O
Jupiter	O
Cantab	O
)	O
.	O
</s>
<s>
Memotech	O
Keyboard	B-Device
,	O
by	O
Memotech	O
.	O
</s>
<s>
1982	O
-	O
Original	O
Jupiter	B-Language
Ace	I-Language
in	O
a	O
vacuum-drawn	O
case	O
-	O
Reported	O
5000	O
units	O
built	O
.	O
</s>
<s>
1983	O
-	O
Jupiter	B-Language
Ace	I-Language
4000	O
on	O
stronger	O
injection	O
moulded	O
case	O
-	O
Reported	O
800	O
units	O
built	O
.	O
</s>
