阅读理解 To avoid any confusion, it is worth stating explicitly that in this book, as in computer science in general, metric units are used instead of traditional English units (the furlong-stone-fortnight system). The principal metric prefixes are listed in Fig. 1-39. The prefixes are typically abbreviated by their first letters, with the units greater than 1 capitalized (KB, MB, etc.). One exception (for historical reasons) is kbps for kilobits/sec. Thus, a 1-Mbps communication line transmits 10^6 bits/sec and a 100-psec (or 100-ps) clock ticks every 10^ − 10 seconds. Since milli and micro both begin with the letter “ m ” , a choice had to be made. Normally, “ m ” is used for milli and “μ” (the Greek letter mu) is used for micro. 为了避免混淆,值得明确指出的是,在这本书中,如同在计算机科学中一般,使用公制单位,而不是传统的英制单位(弗隆 / 浪 -14 磅 -14 天系统)。主要的度量前缀如图 1-39 所示。这些前缀通常由其首字母缩写,再加上单位的首字母缩写(比如 KB 、 MB 等)。一个例外(出于历史原因)是千位 / 秒的 Kbps 。因此, 1Mbps 通信线路可以传输发送 10^6 位 / 秒,每 10^−10 秒有 100 psec (或 100 ps )时钟滴答。由于 milli 和 micro 都以字母“ m ”开头,所以必须做出选择。通常,“ m ”用于 milli ,而“μ”(希腊字母 mu )用于 micro 。 It is also worth pointing out that for measuring memory, disk, file, and database sizes, in common industry practice, the units have slightly different meanings. There, kilo means 2^10 (1024) rather than 10^3 (1000) because memories are always a power of two. Thus, a 1-KB memory contains 1024 bytes, not 1000 bytes. Note also the capital “ B ” in that usage to mean “ bytes ” (units of eight bits), instead of a lowercase “ b ” that means “ bits ” . Similarly, a 1-MB memory contains 2^20 (1,048,576) bytes, a 1-GB memory contains 2^30 (1,073,741,824) bytes, and a 1-TB database contains 2^40 (1,099,511,627,776) bytes. However, a 1-kbps communication line transmits 1000 bits per second and a 10-Mbps LAN runs at 10,000,000 bits/sec because these speeds are not powers of two. Unfortunately, many people tend to mix up these two systems, especially for disk sizes. To avoid ambiguity, in this book, we will use the symbols KB, MB, GB, and TB for 2^10, 2^20, 2^30, and 2^40 bytes, respectively, and the symbols kbps, Mbps, Gbps, and Tbps for 10^3, 10^6, 10^9, and 10^12 bits/sec, respectively. 另外,值得指出的是,对于计算内存、磁盘、文件和数据库大小的计量单位,在通常的行业实践中,这些单元的含义略有细微区别。在这里, kilo 的意思是 2^10 ( 1024 ),而不是 10^3 ( 1000 ),因为内存容量总是 2 的幂次方。因此, 1KB 内存包含 1024 个字节,而不是 1000 个字节。还请注意,该用法中的大写“ B ”表示“字节” bytes ( 8 个比特),而不是小写“ B ”表示“位” bit 。同样, 1MB 内存包含 2^20 ( 1048576 )个字节, 1GB 内存包含 2^30 ( 1073741824 )个字节, 1TB 数据库包含 2^40 ( 109951162776 )字节。然而, 1kbps 通信线路每秒传输 1000 位,而 10Mbps 局域网以 10 000 000 位 / 秒的速度运行,因为这些速度不是 2 的幂次方。不幸的是,许多人倾向于把这两个系统混为一谈,特别是对于磁盘大小。为了避免歧义,在本书中,我们将分别使用符号 KB 、 MB 、 GB 和 TB 表示 2^10 、 2^20 、 2^30 和 2^40 字节,使用符号 Kbps 、 Mbps 、 Gbps 和 Tbps 表示 10^3 、 10^6 、 10^9 和 10^12 位 / 秒。