<s>
Threshold	O
is	O
a	O
space-themed	O
fixed	O
shooter	O
written	O
by	O
Warren	O
Schwader	O
and	O
Ken	O
Williams	O
for	O
the	O
Apple	B-Device
II	I-Device
and	O
published	O
by	O
On-Line	O
Systems	O
in	O
1981	O
.	O
</s>
<s>
Inspired	O
by	O
Sega	O
's	O
Astro	B-Application
Blaster	I-Application
arcade	O
video	O
game	O
,	O
Threshold	O
introduces	O
many	O
enemy	O
ship	O
types	O
and	O
wave	O
formations	O
as	O
the	O
game	O
progresses	O
.	O
</s>
<s>
Ports	O
to	O
other	O
systems	O
were	O
released	O
on	O
ROM	O
cartridge	O
:	O
Atari	B-Device
8-bit	I-Device
family	I-Device
and	O
VIC-20	B-Device
in	O
1981	O
,	O
Commodore	O
64	O
in	O
1983	O
,	O
and	O
ColecoVision	B-Device
and	O
Thomson	B-Device
computers	I-Device
in	O
1984	O
.	O
</s>
<s>
An	O
Atari	B-General_Concept
2600	I-General_Concept
adaptation	O
was	O
published	O
by	O
Tigervision	O
in	O
1982	O
.	O
</s>
<s>
Schwader	O
also	O
wrote	O
the	O
1983	O
Apple	B-Device
II	I-Device
platform	O
game	O
Sammy	B-Application
Lightfoot	I-Application
.	O
</s>
<s>
As	O
in	O
Astro	B-Application
Blaster	I-Application
,	O
firing	O
the	O
laser	O
increases	O
its	O
temperature	O
,	O
and	O
it	O
cools	O
when	O
not	O
in	O
use	O
.	O
</s>
<s>
The	O
game	O
was	O
inspired	O
by	O
Ken	O
Williams	O
playing	O
an	O
Astro	B-Application
Blaster	I-Application
arcade	O
machine	O
in	O
a	O
store	O
and	O
calling	O
Warren	O
Schwader	O
.	O
</s>
<s>
Williams	O
only	O
worked	O
on	O
the	O
project	O
for	O
two	O
weeks	O
of	O
that	O
time	O
,	O
writing	O
the	O
Apple	B-Device
II	I-Device
animation	O
routines	O
.	O
</s>
<s>
Tigervision	O
's	O
Atari	B-General_Concept
2600	I-General_Concept
port	O
received	O
a	O
"	O
Certificate	O
of	O
Merit	O
"	O
in	O
the	O
"	O
Best	O
Science	O
Fiction/Fantasy	O
Videogame	O
"	O
category	O
of	O
the	O
1983	O
Arcade	O
Awards	O
.	O
</s>
<s>
Reviewing	O
the	O
Apple	B-Device
II	I-Device
original	O
for	O
Creative	B-General_Concept
Computing	I-General_Concept
,	O
David	O
Lubar	O
wrote	O
,	O
"	O
The	O
animation	O
in	O
Threshold	O
is	O
superb	O
"	O
,	O
and	O
he	O
found	O
the	O
number	O
of	O
enemy	O
types	O
and	O
waves	O
to	O
be	O
a	O
strong	O
point	O
.	O
</s>
<s>
The	O
Book	O
of	O
Atari	O
Software	O
1983	O
gave	O
the	O
Atari	B-Device
8-bit	I-Device
port	O
a	O
B	O
rating	O
:	O
"	O
It	O
's	O
the	O
usual	O
scenario	O
,	O
with	O
this	O
exception	O
:	O
the	O
game	O
offers	O
unusual	O
depth	O
and	O
variety.	O
"	O
</s>
<s>
Appraising	O
the	O
Atari	B-Device
8-bit	I-Device
computer	I-Device
version	O
,	O
Electronic	O
Games	O
noticed	O
the	O
Astro	B-Application
Blaster	I-Application
connection	O
and	O
wrote	O
"	O
The	O
graphics	O
in	O
Threshold	O
are	O
tremendous.	O
"	O
</s>
