B树、B+树学习之一

磁盘参数RPM是Revolutions Per Minute的缩写

revolution

n. 革命；旋转；运行；循环
这么说，旋转就是革命了。

《算法导论》第三版第279页：

对存储在磁盘上的一颗大的B树，通常看到分支因子在50~2000之间，具体取决于一个关键字相对于一页的大小。一个大的分支因子可以大大地降低树的高度以及查找任何一个关键字所需的磁盘存取次数。

块的概念：

《深入分析Linux内核源码》，http://oss.org.cn/kernel-book/ch09/9.1.htm。

9.1 基本概念

在上一章中，我们把Ext2、Minix、Ext等实际可使用的文件系统称为具体文件系统。具体文件系统管理的是一个逻辑空间，这个逻辑空间就象一个大的数组，数组的每个元素就是文件系统操作的基本单位——逻辑块，逻辑块是从0开始编号的，而且，逻辑块是连续的。与逻辑块相对的是物理块，物理块是数据在磁盘上的存取单位，也就是每进行一次I/O操作，最小传输的数据大小。我们知道数据是存储在磁盘的扇区中的，那么扇区是不是物理块呢？或者物理块是多大呢？这涉及到文件系统效率的问题。

https://en.wikipedia.org/wiki/Block_(data_storage)

In computing (specifically data transmission and data storage), a block, sometimes called a physical record, is a sequence of bytes or bits, usually containing some whole number of records, having a maximum length, a block size.^[1] Data thus structured are said to be blocked. The process of putting data into blocks is called blocking, while deblocking is the process of extracting data from blocks. Blocked data is normally stored in a data buffer and read or written a whole block at a time.

可以参考：http://blog.csdn.net/liuaigui/article/details/6168186。

http://stackoverflow.com/questions/12345804/difference-between-blocks-and-sectors

https://en.wikipedia.org/wiki/Disk_sector

In the 1970s IBM introduced the Direct Access Storage Device (DASD) with fixed-block architecture using sizes of 512, 1024, 2048, or 4096 bytes. Cray Research had an 819 disk controller in 1975 that transferred 512 64-bit words (4096 bytes) per sector. Later,^[^specify^] hard disk drives supporting 1,024-byte sectors began to be integrated into consumer electronics devices such as portable media players and digital video cameras.^[^{citation
needed}^] However, by far the majority of hard drives shipped up to the start of the 2010s still used the traditional 512-byte sector size.