For this exam, you may not consult with people other than Jeff Ondich. Otherwise, you may use any sources of information, including books and the Internet.

The first question in the Java section below will be worth 15 points. Each of the rest of the numbered questions will be worth 5 points.

Most of the questions on this exam can be answered correctly in very few sentences. Brevity and clarity are desirable, so feel free pursue them both.

Have fun.

I: The Java Virtual Machine

One of the most interesting features of Java is the means by which its designers intended it to be translated into machine language. Part of the specification of Java is the specification of the Java Virtual Machine. The JVM has a relatively simple instruction set that has many features in common with most assembly languages, including the MIPS and PDP8/E assembly languages. The JVM instructions are called bytecodes, for reasons that you will discover.

When you compile a Java program, you don't compile it directly into the machine language of a particular processor. Instead, you compile it into the JVM instruction set. The resulting bytecode "executable" doesn't run on any real machines directly. But since the bytecodes are like instructions found in most machine languages, the translation from JVM bytecodes to any particular machine language is relatively simple. When Java programs (applets) are shipped from Web server to Web browser, they are sent as bytecodes, which the browser translates (or gets translated by a separate program, usually called a JVM implementation, or just a JVM) to the machine language of the real machine on which the browser is running. This intermediate interpretation step allows the the downloader's browser/JVM/OS combo to enforce security, among other things.

The following questions concern the Java Virtual Machine. You can find the complete JVM specification at http://java.sun.com/docs/books/vmspec/2nd-edition/html/VMSpecTOC.doc.html If this document moves before 11/22/99, please let me know. I've downloaded a complete copy just in case.

1. Discuss the costs and benefits of using bytecodes as an intermediate step between Java and machine languages. What parts of the computing system (considered broadly to include the various levels of hardware and software, as well as the users, hardware designers, compiler writers, applications programmers, etc.) pay the costs, and what parts reap the benefits? One page of discussion will be sufficient for the purposes of this exam (though this question has undoubtly occupied thousands of hours at Sun and elsewhere).

   You might find it interesting in this context to know that one of the earliest implementations of Pascal--UCSD Pascal--used a scheme almost identical to Java's. Its intermediate language was called "p-code," which survived for a while until Turbo Pascal came along (this is an over-simplification of the events, but it is true that Borland, in a sense, exploited a weakness in the p-code idea). Turbo did not use p-code.

2. Briefly describe the JVM instruction format.

3. Both MIPS and JVM have instructions whose main purpose is to support function-calling. Which instructions are they?

4. What is a JVM frame? How is it different from the stack frames you saw g++ generating?

5. Which features of IEEE 754 are not used by JVM?

6. Which JVM opcodes are "reserved?" What does it mean for an opcode to be reserved? What are these opcodes reserved for?

7. Above, I said "the resulting bytecode 'executable' doesn't run on any real machines directly," and when I wrote that sentence for my Fall 1996 CS207 final exam, it was true. Is it still true?

II: Overclocking

1. In terms of performance as measure in Patterson and Hennessy, pages 62-63, how does overclocking improve performance? If viewed through the lens of Amdahl's law, is overclocking a productive way to improve performance, or not?

2. According to Tom, there's one big danger in overclocking your computer. What is it? How does he recommend you deal with that danger?

3. Evidently, many people believe overclocking to be unethical. Based on Tom's rebuttal, briefly reconstruct their arguments. Do you agree with Tom, his critics, or neither?

4. What has Intel done to prevent overclocking? Under what conditions does Tom say that Intel has chosen not to prevent overclocking, and why?

5. To what does Tom attribute most reports of "unoverclockable" AMD K6 chips?

III: Unicode

1. Briefly, what is Unicode?

2. What organization or organization is responsible for the creation and maintenance of the Unicode standard?

3. List two languages that you have never heard of that are supported by Unicode. Where and by whom are these languages spoken?

4. What is the difference between a glyph and a character? Which one does Unicode specify?

5. In what sense is Unicode compatible with ASCII?

6. If you wanted to get a new character or script added to Unicode (ancient Egyptian, say, or maybe Klingon...), how would you need to proceed?

IV. That's all, folks