reentrant supervisory code

Basing on the analysis of DOS system it has solved successfully the problems of about design and realization of code rewriting, task suspended and resume, screen preservation and restoration in DOS state.

本文就在DOS状态下如何实现屏幕保护进行了研究和探讨，在全面剖析DOS的基础上，成功地解决了代码重入、任务切换、汉字系统伪文本方式的识别，计算机屏幕的保护与恢复等设计DOS下屏幕保护程序的难题，实现了DOS下的屏幕保护。