<s>
Twin	B-Application
Kingdom	I-Application
Valley	I-Application
is	O
a	O
text	O
adventure	B-Application
game	O
with	O
animated	O
pictures	O
(	O
on	O
most	O
formats	O
)	O
for	O
the	O
BBC	B-Device
Micro	I-Device
,	O
Acorn	B-Device
Electron	I-Device
,	O
Commodore	O
64	O
,	O
Commodore	B-Operating_System
16	I-Operating_System
,	O
and	O
ZX	B-Operating_System
Spectrum	I-Operating_System
.	O
</s>
<s>
It	O
was	O
released	O
in	O
1983	B-Application
by	O
Bug-Byte	O
.	O
</s>
<s>
Twin	B-Application
Kingdom	I-Application
Valley	I-Application
is	O
a	O
work	O
of	O
interactive	O
fiction	O
where	O
the	O
player	O
enters	O
commands	O
such	O
as	O
"	O
take	O
jug	O
"	O
at	O
a	O
command	O
prompt	O
and	O
is	O
told	O
the	O
outcome	O
of	O
their	O
move	O
(	O
"	O
I	O
have	O
it	O
now	O
"	O
)	O
.	O
</s>
<s>
It	O
was	O
one	O
of	O
the	O
first	O
text	O
adventure	B-Application
games	O
to	O
have	O
active	O
non-player	O
characters	O
.	O
</s>
<s>
In	O
the	O
original	O
BBC	B-Device
Micro	I-Device
game	O
,	O
there	O
were	O
a	O
limited	O
number	O
of	O
locations	O
and	O
graphics	O
.	O
</s>
<s>
The	O
game	O
was	O
inspired	O
by	O
the	O
original	O
Adventure	B-Application
by	O
Will	O
Crowther	O
.	O
</s>
<s>
The	O
original	O
game	O
engine	O
was	O
written	O
in	O
6502	B-General_Concept
assembly	B-Language
language	I-Language
.	O
</s>
<s>
The	O
game	O
was	O
then	O
ported	O
to	O
Z80	B-General_Concept
for	O
the	O
Spectrum	O
.	O
</s>
<s>
At	O
that	O
time	O
,	O
access	O
to	O
the	O
"	O
massive	O
machines	O
"	O
(	O
by	O
the	O
standards	O
of	O
the	O
day	O
)	O
needed	O
to	O
run	O
the	O
original	O
adventure	B-Application
were	O
limited	O
.	O
</s>
<s>
Twin	B-Application
Kingdom	I-Application
Valley	I-Application
features	O
175	O
rooms	O
.	O
</s>
<s>
A	O
major	O
section	O
of	O
the	O
software	O
is	O
a	O
custom	O
graphics	O
language	O
,	O
which	O
is	O
an	O
early	O
scalable	B-Application
vector	I-Application
graphics	I-Application
format	O
.	O
</s>
<s>
If	O
you	O
use	O
6502	B-General_Concept
to	O
:	O
load	O
register	O
x	O
with	O
the	O
x	O
coordinate	O
,	O
load	O
register	O
y	O
with	O
the	O
y	O
coordinate	O
,	O
load	O
accumulator	O
with	O
a	O
color	O
,	O
and	O
then	O
call	O
"	O
Draw	O
line	O
"	O
,	O
you	O
have	O
used	O
up	O
9	O
bytes	O
.	O
</s>
<s>
To	O
decode	O
this	O
efficiently	O
,	O
just	O
2	O
bits	O
are	O
needed	O
to	O
resolve	O
"	O
Move	O
,	O
Draw	O
,	O
Fill	O
,	O
"	O
any	O
other	O
instruction	O
"	O
in	O
an	O
assembly	B-Language
language	I-Language
.	O
</s>
<s>
The	O
assembly	B-Language
language	I-Language
has	O
no	O
concept	O
of	O
variables	O
,	O
and	O
no	O
branching	O
instructions	O
.	O
</s>
<s>
All	O
of	O
this	O
compression	O
was	O
needed	O
to	O
fit	O
the	O
game	O
within	O
the	O
32k	O
limit	O
or	O
the	O
original	O
BBC	B-Device
Micro	I-Device
system	O
.	O
</s>
<s>
There	O
are	O
roughly	O
180	O
locations	O
in	O
early	O
editions	O
(	O
such	O
as	O
that	O
of	O
the	O
BBC	B-Device
Micro	I-Device
)	O
,	O
and	O
190	O
in	O
later	O
editions	O
(	O
such	O
as	O
the	O
Commodore	O
64	O
version	O
)	O
.	O
</s>
<s>
The	O
game	O
engine	O
has	O
been	O
ported	O
,	O
from	O
the	O
original	O
6502	B-General_Concept
,	O
into	O
Java	B-Language
,	O
with	O
some	O
game	O
design	O
tools	O
in	O
C#	B-Application
.	O
</s>
<s>
Here	O
are	O
the	O
ratings	O
given	O
by	O
Crash	O
Magazine	O
,	O
for	O
the	O
ZX	B-Operating_System
Spectrum	I-Operating_System
version	O
:	O
</s>
<s>
That	O
review	O
comments	O
on	O
the	O
peculiarities	O
which	O
occur	O
when	O
porting	O
games	O
from	O
the	O
BBC	B-Device
micro	I-Device
or	O
C64	O
to	O
the	O
ZX	B-Operating_System
Spectrum	I-Operating_System
.	O
</s>
