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Homework #1

Memory System Architecture
Prof. Philip Koopman

Due Wednesday September 2, 1998

Homework problems are very short answer -- in most cases 10 words or less or a simple equation suffices. Long essays are not desired.

Lecture 2: Key Concepts

1) What do these improve: latency, bandwidth, or both?

• a) A bank opens an additional teller for customers waiting in a line
• b) An additional lane is built onto an existing 4-lane highway to make it 6-lane
• c) The speed limit is increased on a highway
• d) A highway into a major city has an existing lane converted into a lane for buses only (and the buses make heavy use of that lane)
• e) A student runs to class instead of walking to class at CMU.

2) An embedded system project engineer follows a project through the following phases: 2 months design definition; 1 month requirements; 3 months design; 4 months prototype/debug; 2 months transition to production. What is the total speedup for time to market if CAD tools double design productivity (in terms of elapsed time for design phase)?

3) You walk into a building and see a bank of 4 elevators, all controlled by separate up/down request buttons (this is seen in some inexpensive European elevators). In other words, there are four "up" buttons in the lobby, each independently controlling a different elevator.

• a) How would you apply the concept of "hierarchy" to the buttons (and control machinery listening to them) to provide better overall service?
• b) People are densely crowded into the lobby waiting for elevators. Is this a latency problem or a bandwidth problem?
• c) Someone adds a fifth elevator at great expense. If you are the only one in the lobby, how do you expect this to affect your latency compared to the original system?

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