q4 (1) Computer Structures - MASSACHUSETTS INSTITUTE OF...

6.004 Spring 2010 - 1 of 4 - Quiz #4
M A S S A C H U S E T T S I N S T I T U T E O F T E C H N O L O G Y
DEPARTMENT OF ELECTRICAL ENGINEERING AND COMPUTER SCIENCE
6.004 Computation Structures
Spring 2010
Quiz #4: April 23, 2010
Name Athena login name Score
TA: Kevin
 WF 10, 34-303
TA: Erica
 WF 12, 34-302
TA: Sabrina
 WF 1, 34-301
TA: Nicole
 WF 2, 34-302
 WF 11, 34-303  WF 1, 34-302  WF 2, 34-301  WF 3, 34-302
Problem 1 (8 points): Quickies-but-Trickies
(A) (2 points) Beta application programmers are told to avoid storing data in XP . If they
violate this rule, will interrupt returns fail to work? Will OS kernel data be lost? Will
application data be lost? Circle all that apply, or NONE :
XP usage breaks: Interrupt returns … Kernel data … App data … NONE
(B) (2 points) A Beta processor has an interrupt handler invoked by a periodic 60Hz clock.
The handler simply inspects the high-order bit of the XP register to see if it is a 1 or 0.
Give your best estimate of the fraction of the time it finds a 0.
Mark one: 0%: _____ or 50%: _____ or 100%: _____
(C) (2 points) You are evaluating two tiny 4-line caches, each with a total storage of four data
words. Model DM is direct-mapped, and model FA is fully associative (LRU). Each
uses word addressing (hence consecutive addresses differ by 1, not 4 as in the Beta).
The benchmark involves just six memory reads, starting with an empty (invalidated)
cache. Finish the reference string given below to yield an access pattern that will give a
better hit rate on DM than on FA . Fill in the final two additional memory addresses, or
circle “NONE” if no such reference string exists. Use single-digit decimal addresses.
References to: 0, 1, 2, 3, _____, _____ or circle: NONE
(D) (2 points) Same setup; this time give references that make FA look better or circle
“NONE”. Again, use single-digit decimal addresses.