Homework 1 examples

Purposes:
   (1) work with units and prefixes;
   (2) work with the execution time equation and CPI.

Note:
   For main memory size, interpret K, M, and G as powers of two.
   Otherwise, interpret K, M, and G as powers of ten.



1. For a processor with 100 MHz clock frequency (a.k.a. clock rate),
   what is the clock cycle time?

   CCT = 1 / clock rate = 1 / ( 100 * 10^6 cycles per sec )
       = 10 / 10^9 secs per cycle = 10 nsec


2. Consider making a complete backup of a full 40 GB hard drive using a
   250 MB zip drive.  How many 250 MB zip disks will be needed?

   Use powers of ten for capacities other than cache or main memory.

   # of zip disks = 40 GB / 250 MB = 4*10^10 / 2.5*10^8 = 160

   
3. Find the execution time for a program that executes 30 million
   instructions on a processor with an avg. CPI of 2.0 and a clock
   cycle time of 33.3 nsec.

   exec. time = IC * CPI * CCT
              = 30M insts. * 2 cycles/inst * 33.3 nsec/cycle
              = 1.998 seconds = 2 seconds (rounded)


4. For the following instruction set workload and cycle values, find the
   average CPI.

      type   |  freq  cycles
      -------+--------------
      alu    |  0.5     2
      branch |  0.2     6
      ld/st  |  0.3     6

   avg. CPI = (0.5 * 2) + (0.2 * 6) + (0.3 * 6) = 4.0