OS Operating System reference URL 2018-06-102019-04-14 http://uclab.khu.ac.kr/lectures/2013-1_os.html?PHPSESSID=72d3997d777ff609654c593e49a26444 https://m.blog.naver.com/mkt0716/30031141099 http://www.kocw.net/home/search/kemView.do?kemId=1194929 http://cafe307.daum.net/_c21_/bbs_search_read?grpid=5It&fldid=B8J&datanum=652&contentval=&docid=5ItB8J65220051113201900 http://jiming.tistory.com/173