Apollo Guidance Computer

Dan Roganti ragooman at comcast.net
Sun Sep 21 20:28:57 CDT 2008



Dan wrote:
> I feel this would make some people scratch their heads :)
>
> What type of arithmetic operations were used to perform all the 
> calculations on the Apollo Guidance Computer ?
>
> a) Floating Point arithmetic operations
> b) Fixed Point Arithmetic operations
> c) Integer Arithmetic operations
> d) Slide Rule Arithmetic operations
> e) all of the above

what ? everyone still scratching their heads on this one :)
Ok, the answer would be d) slide rule

If anyone remembers using their slide rule, you happen to be using 
Fractional Arithmetic. If I wrote this down for answer d) it may have 
been obvious to some, so I thru a little twist into it. The Apollo 
programmers always coded their calculations as if they were using a 
slide rule(this was the early 60's remember). They would have to keep 
track on paper of the equation's dynamic range(also anticipate how large 
this range could become) since the design didn't incorporate exponents 
within the answer(as would be found in a FPU).

BTW, the HP-65 calculator was used as the backup computer on later 
missions, since it was too programmable.

=Dan

[ Pittsburgh 250th --- http://www2.applegate.org/~ragooman/   ]





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