BCL和FCL
BCL：ase Class Library 是CLI的一部分，是CLR的一部分（CLR 是CLI在window平台的一种实现，另外 Rotor和Mono也对CLI进行实现）。
在Professional .Net Framework 2.0 （ .Net Framework 2.0 高级编程）一书中就BCL讲述了基本类型，数组，集合，I/O,文件，网络互连，国际化等主题。
下面是来自Standard ECMA-335 Common Language Infrastructure (CLI) 4th edition (June 2006)的摘录：
http://www.ecma-international.org/publications/standards/Ecma-335.htm（ECMA-335.pdf）
5.3 Base Class Library (BCL)
The Base Class Library is part of the Kernel Profile. It is a simple runtime library for modern programming
languages. It serves as the Standard for the runtime library for the language C# as well as one of the CLI
Standard Libraries. It provides types to represent the built-in data types of the CLI, simple file access, custom
attributes, security attributes, string manipulation, formatting, streams, collections, among other things.
FCL:不是CLR的一部分，是微软在BCL基础上创建的各种类库，如WinForms, Data等。
参考：http://www.thedatafarm.com/blog/PermaLink.aspx?guid=059890a2-fc5f-416a-9b29-7ec411ab4293