Amdahl's law of processors (infinite processors to test limits of speedup) My processor noted that an infinite number of processors will allow me to test how much speedup I can achieve. 

I am not exactly sure how this applies. 

For instance, let's say I have a program that takes $1000$ seconds to execute and is broken into 4 phases(A, B, C, D). If two of the phases are $50%$ parallelizable and the other $2$ are not parallelizable at all, how can I apply the concept that I have infinite available processors to figure out how much maximum speed up I can achieve? 

I attached numbers to my example, but a generic one would be just as helpful. 

If I am to strictly just apply Amdahl's law, I'd say the answer is just $1/(1-0.5) = 2$ times faster.
Don't think of it as "you've been given infinity processors." Think of it as "you can have as many processors as you want, but of course after a certain point more professors won't help, so find out how fast you can make it run with the optimum number of processors."