共享内存（msdn的一个文件判断的解释)

共享内存（msdn的一个资料判断的解释)
For example, suppose that the GetSystemInfo function indicates an allocation granularity of 64K. To examine 1K of data that is 138,240 bytes (135K) into the file, do the following:

  Create a file mapping object of at least 139,264 bytes (136K) in size.
  Create a file view that starts at a file offset that is the largest multiple of the file allocation granularity less than the offset you require. In this case, the file view starts at offset 131,072 (128K) into the file. The view is 139264 bytes (136K) minus 131,072 bytes (128K), or 8,192 bytes (8K), in size.
  Create a pointer offset 7K into the view to access the 1K in which you are interested.


http://msdn.microsoft.com/en-us/library/windows/desktop/aa366548%28v=vs.85%29.aspx#feedback

这个英文片段看了好几次，一直没有看懂

求解释

------解决方案--------------------
如果你要查看一个文件的第 139,264字节起的1K数据，你需要创建一个至少131,072 +1k=132,096字节的文件映射对象。之后从文件映射创建的视图的起始地址是131,072，长度是1k字节。这个示例假定操作系统的内存分配粒度是64k.
------解决方案--------------------
前后就是个相对概念，我不太注意随口说的。就是你理解的从高地址跳到低地址。
另别叫老师，我也是个菜鸟，互相学习。