CMSC 411 Sample Final Exam Questions General instructions Be complete yet concise You may leave arithmetic expressions in any form that a calculator could evaluate 1 Storage systems a Use the data in the following table to compute the average disk access time for one sector in milliseconds average seek time transfer rate rotation speed sector size controller overhead 7 ms 8MB sec 5000 RPM 2048 bytes 1 ms b What is the speedup for disk accesses if we use a disk with more tracks so that average seek time is 9ms but the disk is faster rotating at 9000 RPM and with a transfer rate of 10MB sec 2 Caches We have a 500 MHz processor with 2 levels of cache plus Main Memory Assume that the first level cache contains separate instruction and data caches while the second level cache is unified The memory system has the following parameters First Level Cache Hit Time 1 cycle Second Level Cache Main Memory 20 cycles 50 cycles Miss Rate 4 Data 1 Instructions 2 Block Size 64 bytes 128 bytes 16 Kbytes Finally the bus parameters are as follows L1 cache L2 cache bus 1 cycle word L2 cache Memory bus 5 cycles word You can also assume that 1 word is 8 bytes a What is the average memory access time in nanoseconds for instructions b What is the average memory access time in nanoseconds for data reads 3 CPU performance Suppose we have the following instruction mix and clock cycles per instruction Instruction ALU operations Load Store Branches Floating point operations Frequency 40 15 10 20 15 Cycles 1 2 2 3 6 Suppose our computer has the following specifications CPU 720MHZ Main Memory 128MB a What is the overall CPI of this machine b What is the MIPS rating of this machine c Consider improving this computer s performance by enhancing the speed of the floating point instructions What is the best possible overall speedup that we could obtain 4 Short answers Each question should be answered in no more than three or four not too long sentences a Storage Systems In a RAID system why does using a single parity disk cause performance problems Name one method for alleviating the performance problems If one of the disks data or parity fails what information is needed to reconstruct the data for a block interleaved parity RAID system b Hardware ILP What performance benefits can hardware based speculation provide that branch prediction with dynamic scheduling cannot What are the associated costs c Buses Describe one advantage a synchronous bus has over an asynchronous bus and one advantage an asynchronous bus has over a synchronous bus d Multiprocessors Describe one feature that is shared between snooping and directory based multiprocessor cache coherence protocols Also describe one difference between the 2 types of protocols
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