tailieunhanh - A Technical History of Apple’s Operating Systems phần 4

Một số NLS thành viên trong nhóm đã đến sau đó mới ra đời Xerox PARC, nơi họ hy vọng tạo ra một phân phối (trên mạng)-chứ không phải là thời gian chia sẻ phiên bản của NLS. Tệ hơn nữa, SRI giảm chương trình, để lại không có kinh phí cho dự án. Engelbart đã đi đến một công ty mạng điện thoại được gọi là Tymshare | 36 Chapter 1 A Technical History of Apple s Operating Systems . Worms An interesting investigation involving networked Alto computers was with worm programs. In 1975 science fiction writer John Brunner had written about such programs in his book The Shockwave Rider. PARC researchers John F. Shoch and Jon A. Hupp experimented with worm programs in the early 1980s. The experimental environment consisted of over a hundred Ethernet-connected Altos. A worm was simply a multimachine computation with each machine holding a segment of the worm. Segments on various machines could communicate with each other. If a segment was lost say because its machine went down the remaining segments would search for an idle Alto on which to load a new copy self-repairing software. It is important to note that the idea behind the worm experiments was not that of mischief. The researchers intended to create useful programs that would utilize otherwise idle machines essentially a form of distributed Nevertheless the aberrant potential of worms was clearly identified although worms were still not perceived as a real security risk. Comparatively viruses and self-replicating Trojan horse programs were considered bigger threats to security. Examples of applications that used such worms include the following. The Existential worm was a null worm that only contained logic for its own survival. The Billboard worm could distribute graphics images to multiple machines. The Alarm Clock worm was a distributed fault-tolerant computer-based alarm clock that could call a user on the telephone at a designated time. The Multimachine Animation worm was part of a distributed real-time animation mechanism involving multiple compute nodes and a single master node. 26 The Alto worms were conceptually similar in some aspects to the controller and agent programs in a modern-day grid-computing environment such as Apple s Xgrid. Mac OS X Internals 37 The Ethernet Diagnostic worm