This is a an exam. You may consult your notes, any book, and the Internet. You may not speak with any person other than Jeff Ondich, electronically or otherwise, about the content of this exam. If you obtain relevant information from any source other than yourself, cite your sources clearly. Justify your answers. (Note that "justify your answers" implies "show your work.") Have fun.
(10 points) Consider the single-cycle datapath shown in Figure 4.21 in Patterson and Hennessy, and imagine that we're executing the beq instruction at the end of this sequence:
start: add $10, $11, $12 sub $12, $13, $14 addi $9, $8, 25 beq $4, $5, start
Suppose the beq instruction is located at address 75000 and the contents of registers $4 and $5 are 5361 and 7162, respectively. Suppose further that we have executed this instruction up through the very end of its clock cycle, but that the clock has not yet fallen to end the cycle. Print (or edit as a PDF or JPG or...) Figure 4.21 and show the values of as many lines on the datapath as possible. This includes control lines, lines whose values are used during this cycle, lines whose values are not used during this cycle, lines whose values are left over from old cycles, etc.
(8 points) Using our PDP-8 datapath, suppose the propagation delays of the various elements are: 8 ns to read memory, 4 ns for the ALU, 3 ns for the Control, 2 ns for each of the multiplexors, and 4 ns for each of the circular/oval units (e.g. Shift Logic, To EA, +1, PCWE, and AC/L Logic). Also, assume that the memory elements PC, Memory, IR, AR, and L/AC show the proper output 1 ns after the trailing clock edge (assuming the appropriate write-enable lines are set).
Consider executing the "TAD I A" instruction, using our usual datapath cycle diagram. For each cycle required to execute this instruction, what amount of time is required to complete that cycle's work? Based only on TAD I A, then, what is the fastest allowable clock rate for this datapath?
(2 points) Take your pick: recommend a movie, tell me a joke, or point me to something cool on the Internet.
(20 points) This part of the exam concerns the first few pages of John von Neumann's First Draft of a Report on the EDVAC. Read it and answer the following questions. For the first three questions, which concern the historical context of this report, you may need to look elsewhere for information.
In an earlier edition of your textbook, Patterson and Hennessy note that von Neumann's report report was one of several things that attorneys used to break the Mauchly/Eckert patent on the computer. This point is also made on the brief Wikipedia page about the EDVAC report. What besides this report was relevant in the patent case?
Who besides von Neumann deserves credit for this report?
During the 1940's, several women were heavily involved in the development and operation of the ENIAC. Name at least two of them, and briefly describe their roles in the project.
Throughout the Draft Report, von Neumann refers to the main subdivisions of a computing system as CA, CC, I, O, R, and M. To what modern concepts do these six subdivisions refer?
What does von Neumann means by the term elastic in section 2.3? He also advocates separating some things in the interests of elasticity. What does he want to separate, and how does this separation serve the goals of elasticity?
There is a sentence in section 2.9 that begins with "As to (h) (sorting and statistics), the situation is somewhat ambiguous...." This sentence hints at the subject of one of the chapters in Patterson and Hennessy. Which chapter?
Clarify the first paragraph of section 4.1. You might find it handy to include an example or two using modern gate language.
Summarize von Neumann's arguments in favor of binary rather than decimal computation. Are these arguments still valid?
Why does von Neumann like vacuum tubes? (Vacuum tubes, by the way, are devices that can be used to perform switching operations like those done by transistors. Thus, you could build gates out of vacuum tubes. Vacuum tubes tended to burn out like light bulbs do, so it was common for drug stores and hardware stores to sell them. When I was a kid, our neighborhood drug store had a kiosk where you could bring in a burnt-out tube and stick it into the plugs on the kiosk to figure out which replacement tube would work. This was necessary if you wanted your TV to keep working.)
Consider the last paragraph of section 5.6. In what ways is von Neumann's advice still valid, and in what ways is it not?
