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Cost Calculations (revisited)

Assumptions:
  • disk read time Tr ≅ Tw disk write time
  • average disk read/write time is a large constant value
  • the real measure of cost is number of page↔disk transfers
So, in all future analyses, we ignore Tr and Tw
  • measure Cost as number of pages read and written
Also, when comparing two algorithms for same task
  • ignore cost of writing result; same in both cases