# Comp150CPA: Clouds and Power-Aware Computing

Classroom Exercise 20

Introduction to Power

Spring 2011

### group member 1: ____________________________ login: ______________

### group member 2: ____________________________ login: ______________

### group member 3: ____________________________ login: ______________

### group member 4: ____________________________ login: ______________

### group member 5: ____________________________ login: ______________

In class we discussed the basic power equations.
Let's use them for some simple calculations.

- Suppose that a person outputs 400 BTU/hour and a computer takes
28 watts. Suppose that 10 people can perform a task together in an hour,
while the computer can accomplish the task in 10 minutes. Compare the
power and energy consumption in the two cases, accounting for air conditioning(!)
(1 watt = 3.41214 BTU/hour).

- Suppose that as in class, we have 40 servers and 40 processes,
each of which takes 10 time units, and that each one has a deadline of 20
time units. Suppose that context-switching overhead is 5%. How many
servers should be running so that the deadlines are met with minimal
energy consumption?

- (Advanced)
Suppose that a server takes x watts of idle power to run, and that
spinning up a disk takes another 30% extra power.
An extra GB of disk cache takes 10% more idle power but reduces
the time the disk is spun up by 30%. To save the most power and energy,
should you add the memory or not?