CSC 8400-001

Examination E2

April 10, 2000


PROBLEM 1 [21%]

Your answer to each part of this question should be clear, to the point and concise - not more than a couple of lines long.

a) What is the difference between the write through and the write back policies?

b) What is the difference between the write allocate and the no write allocate policies?

c) In what kind of caches and for what purpose is the "dirty bit" used?

d) What is the main reason that DRAMs are less expensive and have higher capacity than SRAMs?

e) What is the main reason that DRAMs are slower than SRAMs?

f) What is page table and where is it stored?

g) What is TLB (Translation Lookaside Buffer) and for what purpose is it used?



PROBLEM 2 [10%]

MRU is the replacement policy in caches that chooses the most recently used block for replacement.

  1. What well-known property of programs makes using MRU a bad idea?
  2. Saying just the name of that property (principle) would give you a full credit for this question; no explanation is required.

  3. For each of the following three components of memory access time: 1) hit time, 2) miss rate and 3) miss penalty, indicate whether switching from LRU to MRU, - without changing anything else in the cache, - would generally increase, decrease or not affect that component.



PROBLEM 3 [16%]

Assume the following:

a) What is the block size?

b) How many different blocks map to set 3?

c) How many bits are there in the tag field of the address of a word?

d) If the (physical) address of a word is 18, in which block frames can that word appear?

PROBLEM 4 [6%]

Assume a direct mapped cache only has 2 block frames in it and that the block size is 4 words.

What would be the miss rate for the following code?

1. ADD R1, R1, R1

2. ADD R2, R2, R2

3. ADD R3, R3, R3

4. ADD R4, R4, R4

5. ADD R1, R1, R1

6. ADD R2, R2, R2


PROBLEM 5 [20%]

You have a DLX machine with a unified cache which has the following features:

Assume also that for our benchmark program(s),

What is the real CPI (taking into account memory stalls due to misses)?




PROBLEM 6 [12%]

Consider a machine that has a 2-level cache with the following characteristics:

a) What is the local miss rate in the second level cache?

  1. What is the average memory access time for this machine?


PROBLEM 7 [15%]

a) Write the formula for average disk access time.

  1. If a hard disk is rotating at the rate 3600 RPM, what is the average rotational delay?
  2. The real average seek time is usually only 25%-30% of the advertised average seek time. Why?