<s>
Countdown	B-Application
to	I-Application
Doom	I-Application
is	O
a	O
text	O
adventure	O
game	O
written	O
by	O
Peter	O
Killworth	O
for	O
the	O
BBC	B-Device
Micro	I-Device
and	O
published	O
by	O
Acornsoft	O
in	O
1982	B-Application
.	O
</s>
<s>
An	O
Acorn	B-Device
Electron	I-Device
version	O
was	O
released	O
in	O
1984	O
but	O
only	O
as	O
a	O
ROM	B-Protocol
cartridge	I-Protocol
for	O
the	O
Plus	O
1	O
expansion	O
.	O
</s>
<s>
Topologika	O
rereleased	O
Countdown	B-Application
to	I-Application
Doom	I-Application
in	O
1987	O
,	O
expanding	O
the	O
scope	O
of	O
the	O
game	O
by	O
about	O
50%	O
.	O
</s>
<s>
It	O
was	O
published	O
for	O
the	O
BBC	B-Device
Micro	I-Device
,	O
Acorn	B-Device
Electron	I-Device
,	O
ZX	B-Operating_System
Spectrum	I-Operating_System
,	O
IBM	O
PC	O
compatibles	O
,	O
Amstrad	B-Device
CPC	I-Device
,	O
Amstrad	B-Device
PCW	I-Device
,	O
Atari	B-Device
ST	I-Device
,	O
and	O
RM	O
Nimbus	O
.	O
</s>
<s>
A	O
RISC	B-Operating_System
OS	I-Operating_System
version	O
was	O
published	O
in	O
a	O
compilation	O
with	O
Return	O
to	O
Doom	O
and	O
Philosopher	O
's	O
Quest	O
.	O
</s>
