题目内容

假定硬盘传输数据以32位的字为单位，传输速率为1MB/s。CPU的时钟频率为50MHz。采用DMA控制器进行输入输出操作，假定DMA的启动操作需要1000个时钟周期，DMA完成时处理中断需要500个时钟周期。如果平均传输的数据长度为4KB(此处，1MB=1000KB)，问在硬盘工作的一次传输中，处理器将用多少时间比重进行输入输出操作，忽略DMA申请使用总线的影响。

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孟德尔选取豌豆作为实验材料，因为它是一种性状的一年生植物。

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Feed the World with Potatoes1 As food prices continue to rise rapidly, there is growing concern about the effect it will have among the world"s poor.2 Increasingly, experts are looking to the potato as a possible low-cost solution to feeding the hungry. To emphasize the issue, the United Nations has called the potato "a hidden treasure", and named 2008 the International Year of the Potato. Here"s how potatoes could end the food crisis.3 The potato matures more quickly, on less land and in harsher climates than most other major crops. Up to 85 percent of the plant is eatable, compared with around 50 percent of cereals. Its broad adaptability to a wide variety of farming systems is also noteworthy.4 Potatoes are an excellent source of complex carbohydrates ( 碳水化合物), which release their energy slowly, and have only 5 percent of wheat"s fat content. They contain only a quarter of the calories of bread and, according to the Potato Center, when boiled, potatoes have more protein and nearly twice the calcium (钙) as corn. Additionally, they are good sources of vitamin C, iron, potassium (钾) and zinc (锌).5 The Food and Agricultural Organization recently surveyed food price inflation in over 70 of the poor countries. Cereal price inflation was much higher and far more widespread than for potatoes. A significant factor behind the potato"s affordability is the fact that unlike other agricultural products, the potato is not yet a global commodity, and has therefore not attracted speculative investors. Raw potatoes are heavy and can rot during transit, so global trade has been slow to take off. Also, potatoes are susceptible (易受影响的) to infection with disease, hindering (阻碍) export. According to analysts" estimates, less than 5 percent of potatoes are traded internationally, with prices driven primarily by local tastes instead of international demand. Paragraph 2 ______ A. Higher Output B. Healthy Food C. Growing Importance of Potatoes D. Potatoes" Lower Inflation E. High Price F. Major Food Crops

以下是计算两个向量点积的程序段：float Dotproduct(float x[8], float y[8]){float sum=0.0;int i;for(i=0; i＜8; i++)sum+=X[i]*y[i];return sum;}请回答下列问题：请分析访问数组x和y时的时间局部性和空间局部性

以下是计算两个向量点积的程序段：float Dotproduct(float x[8], float y[8]){float sum=0.0;int i;for(i=0; i＜8; i++)sum+=X[i]*y[i];return sum;}请回答下列问题：假定数据Cache采用直接映射方式，Cache容量为32字节，每个主存块大小为16字节；编译器将变量sum和i分配在寄存器中，内存按字节编址，数组x存放在0000 0040H开始的32字节的连续存储区中，数组y则紧跟在x后进行存放。该程序数据访问的命中率是多少要求说明每次访问时Cache的命中情况。