SI 540: Fall 1999

HW 2

due October 4

Last modified 9/24/99--PR
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This assignment must be completed individually. You may discuss the LMC with other students (e.g., why the example LMC programs in the readings work the way they do), but it's very important that you work on writing the LMC program yourself.

Reading

Chapter 4, section 1 only, plus the sidebar about operating systems on page 96.
Handout about the Little Man Computer (LMC), by Stuart Madnick.
PC Magazine article on Operating Systems, available online.
Notes on representation, architecture, and programming languages

Lab Exercise

First, you'll need to install a copy of the Little Man Computer Simulator. You'll need to run it on a Windows machine. Click here to download it. It's an executable file: once you've saved it, just double-click to install the software. Thanks to Jim Longfellow, who wrote this version of the simulator while he was a TA for a class at MIT, and thanks to Chris Dellarocas for permission to use it for our class.

Your goal is to create an LMC program that finds the maximum value of all inputs on the input conveyor belt, ending when it finds the value 000 on the input conveyor belt. Use figures 17 and 18 (from the LMC handout) as examples to work from in doing this exercise.

First draw a flowchart for your program, similar to the one in figure 17.
Next write a program, similar to the one in Figure18. Be sure to test it using the LMC simulator. Save the program as a file and also print the LMC screen after a sample run of the program. Send your program as a file attachment, and hand in on paper your flow chart and the printout of the sample run.

Explanation

(Find someone who is not taking this class, and who knows less about computers than you do. It could be a fellow SI student, or a roommate or a friend or relative). Explain to this person what an operating system is. In your homework writeup, say who received your explanation, and include a few sentences about what made it easy or hard to do the explanation.

Questions for Class

Some questions to think about for class (don't hand in answers to these, but be prepared to discuss in class):

Is it possible to create a compiler that would take C++ source programs and create Java bytecode?
Is it possible to create an interpreter for program for Java source code (not Java bytecode)?
Is it possible to create a decompiler program that generates COBOL source code from machine code? How helpful would such a decompiler program be in solving Y2K problems?