计算机体系结构_第一次作业.pdfVIP

计算机体系结构 第一章 1.11 Availability is the most important consideration for designing servers, followed closely by scalability and throughput. a. We have a single processor with a failures in time(FIT) of 100. What is the mean time to failure (MTTF) for this system? b. If it takes 1 day to get the system running again, what is the availability of the system? c. Imagine that the government, to cut costs, is going to build a supercomputer out of inexpensive computers rather than expensive, reliable computers. What is the MTTF for a system with 1000 processors? Assume that if one fails, they all fail. 答： a. 平均故障时间 (MTTF) 是一个可靠性度量方法， MTTF 的倒数是故 障率，一般以每 10 亿小时运行中的故障时间计算 (FIT) 。因此由该 定义可知 1/MTTF=FIT/10 ＾9 ，所以 MTTF=10^9/100=10^7 。 b. 系统可用性 =MTTF/(MTTF+MTTR) ，其中 MTTR 为平均修复时间， 在该题目中表示为系统重启时间。计算 10^7/(10^7+24) 约等于 1. c. 由于一个处理器发生故障，其他处理器也不能使用，所以故障率 为原来的 1000 倍，所以 MTTF 值为单个处理器 MTTF 的 1/1000 即 10^7/1000=10^4 。 1.14 In this exercise, assume that we are considering enhancing a machine by adding vector hardware to it. When a computation is run in vector mode on the vector hardware, it is 10 times faster than the normal mode of execution. We call the percentage of time that could be spent using vector mode the percentage of vectorization. a. Draw a graph that plots the speedup as a percentage of the computation performed in vector mode. Label the y-axis “Net speedup ” and label the x-axis “Percent vectorization ”. b. What percentage of vectorization is needed to achieve a speedup of 2? c. What percentage of the computation run time is spent in vector mode if a speedup of 2 is achieved? d. What percentage of vectorization is needed to