V22.0436 - Prof. Grishman
Practice Final Exam Questions
A processor runs at 100 Mhz. What is the length of its clock cycle?
A disk has an access time of 10 ms. Assuming the time for data transfer
is negligible, how many disk accesses can be performed each second?
Design a fast circuit to compute the sum of two 2-bit positive numbers.
Construct a truth table for such a circuit, and then convert the truth
table into a sum-of-products logic formula for each output. What is the
propagation delay of this circuit, from input to output?
Given D-type master-slave FFs, AND, OR, NAND, NOR gates, inverters, and
multiplexers, design a 4-word, 2 bit per word register file with a single
input port and a single output port.
MIPS Processor Design
Write a MIPS program with a loop which copies the 20 words (80 bytes) beginning
at byte 1000 to the 20 words beginning at byte 2000.
What is the purpose of the 'sign extend' circuit in the MIPS CPU you simulated?
Suppose we didn't have a sign extend circuit; what limitation would there
be on branch instructions?
Is it possible for a program to modify its instructions in the single cycle
MIPS CPU? in the multi-cycle CPU?
Suppose that when program Zippo runs, it executes 200,000 loads, 100,000
stores, 699,998 R-type instructions, and 2 multiply instructions. Consider
2 machine designs: in design M1, the clock rate is 100Mhz; loads and stores
take 2 cycles, R-type instructions take 1 cycle, and multiplies take 5
cycles. In design M2, the clock rate is 66Mhz and all instructions take
1 cycle. Which machine is faster?
Consider two alternative caches, each of which has a capacity of 8 words
and a block size of one word. Cache D is a direct mapped cache, and cache
T is a two-way set associative cache. Suppose the cache is initially empty
and we fetch the words at the following addresses in sequence: 1, 2, 9,
3, 1, 5, 9. Which of these fetches will result in cache hits?
Suppose that we have a 10 ns cache (it takes 10 ns to access the data or
identify a miss), and a memory system with a 100 ns access time. What is
the average memory access time if the cache hit rate is 97%? If we built
a larger cache, with a 12 ns access time but a hit rate of 98%, would the
average memory access time increase or decrease?
Suppose we have a floppy disk which transfers 50 KB and interrupts the
CPU each time a byte is available. The CPU executes approximately 50 mips,
and the interrupt routine takes 25 instructions to transfer a byte to memory.
What fraction of the CPU time will be occupied doing IO with the floppy
Consider a handshaking circuit for asynchronous data transmission, where
the transmitter sets and resets a DATA READY signal, and the receiver sets
and resets an ACKNOWLEDGE signal. Why must the receiver wait for ACKNOWLEDGE
to be reset to 0 before commencing the transmission of the next bit? Indicate
what could go wrong if it didn't.
Final Exam: Wednesday, May 5th, 12:00 - 1:50, Room 109 Warren Weaver