Question

The question:

Assume that cache memory is ten times faster than DRAM memory, that DRAM is 100,000 times faster than magnetic disk, and that flash memory is 1,000 times faster than disk. If it takes 2 microseconds while reading from cache memory, how long does it take to read the same file from DRAM, disk, and flash memory?

Does this require only simple algebra, or are there any complex computations needed?

Answer 1

Given time equivalencies:

    1,000 flash = disk
  100,000 dram  = disk  
1,000,000 cache = disk  (substituted from 10 cache = dram)

Now given cache = 2µs:

disk  = 1,000,000 * 2µs =  2s
dram  = 2s / 100,000    = 20µs
flash = 2s /   1,000    =  2ms