Computer Science Comprehensive Exam
Architecture
May 19, 1997
This is a closed-book exam. Answer all of the questions. Be concise
in your answers, You will receive partial credit for partially correct
answers, but extraneous remarks may count against you.
- Caches
- Explain what it means for a cache to be virtually or physically
tagged, and to be virtually or physically indexed. Do all four
combinations make sense?
- Show with an example cache lookup the
difference between the various combinations that make sense.
- What are the advantages and disadvantages of the various
combinations?
- What combinations occur in current processors? Can you give a
couple of examples?
- I/O Systems
- Define the terms seek time, rotational latency, and transfer time of
a disk, and give typical values for current devices.
- Give and explain three software techniques that file system software
typically uses to get around the slow speed and idiosyncratic access times
of disks.
- Many file servers use a small amount (a few tens of kilobytes)
of nonvolatile memory to speed up their operation. How does that work?
- Superscalar processors
- What is a superscalar processor?
- What memory system support is desirable for a superscalar processor
and why? (Limit to one page at the most.)
- Give an order-of-magnitude value for the execution time improvement
of unmodified code running on a superscalar processor compared to a scalar
one with the same clock speed. Pick a value from the following set:
2, 4, 8, 16, 32, 64. What is the limiting factor in practice?