一台完全无软件的计算机系统称为裸机，即便其性能再强，相对于用户来讲，如果要面对计算机的指令集、存储组织、I/O总线结构的编程则是十分困难的。对于一般程序员也并不想涉足硬件编程的种种具体细节，而希望针对数据结构抽象地使用硬件。如果我们在裸机上覆盖一层I/O设备管理软件，用户便可以利用这层I/O设备管理软件提供给用户的接口来进行数据的输入和输出，那么用户此时看到的计算机是一台功能强大、使用方便的计算机，但实际上，计算机的硬件丝毫没有变化，这样的计算机称为软件扩充的机器，或称软件虚拟机。-complete without a computer software system, known as bare metal, even if another strong performance, relative to the users. If faced with the instruction set computer, storage, I / O bus architecture of the programming is very difficult. For the average programmer does not want to set foot in the hardware programming details, and hope against abstract data structure to the use of hardware. If we cover the bare metal layer on the I / O device management software, users can use this layer I / O device management software for the user interface for data input and output, so users can see at this time of the computer is a powerful, easy-to-use computer, but in reality computer hardware has not changed a bit, such as computer software expansion of the machines, or virtual machine software.