演示实模式下DOS的一个多线程的例子，是来自于网络，经过测试可用-Demonstrates a real mode DOS multi-threaded example is from the network, after testing available

这是一个可以多步回退的例子,使用Command模式,即可以对对象属性回退-This is an example of can step back, using the Command pattern, namely the object properties can be rolled back