37. Acme Corporation has a medical research application that compares observatio

Question

37. Acme Corporation has a medical research application that compares observations from their lab against every item in a 2GB array of data that’s loaded into memory when the application starts. They process about 1,000 observations a day in about 17 minutes of run time. (Each observation takes about one second). The medical director wants to increase the comparison data by a factor of 100, to 200 GB. When told that such a large array will not fit in memory, the medical director replied, “That’s OK, just process against the array on disk.” By how much will this slow down the application? Express your answers as an order of magnitude, that is, as a power of ten. Explain your answer. (Hint: what is the order of magnitude speed difference between disk and CPU? What is the order of magnitude of the increase in data?

Explanation / Answer

Order of magnitude difference is 10^6 for a normal instruction.

but here it wil be 100 *10^6

This is to some extent a comparison between apples and oranges. The assumption is that the basic operation on a CPU takes 1 ns (since the clock frequency is 1 GHz), whereas a basic operation on the hard disk takes 4 ms. The quoted factor is just 4 ms / 1 ns = 4×106.

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