DES是数据加密标准，是IBM公司1975年首先提出的，1977年正式作为美国国家保密局信息处理标准，开始生效。DES使用长度为(10)的密钥对64比特的明文进行加密，获得64比特的密文，使得只有持有合法密钥的人通过解密获得明文，其他人想了解明文是非常困难的。

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MIMD　systems　can　be　classified　into(71)-oriented　systems,　high-availability　systems　and　response-oriented　systems.　The　goal　of(71).　oriented　multiprocessing　is　to　obtain　high(71)(72)minimal　computing　cost.　The　techniques　employed　by　multiprocessor　operating　systems　to　achieve　this　goal　take　advantage　of　an　inherent　processing　versus　input/output　balance　in　the　workload　to　produce(73)and(74)loading　of　system(75).

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Prior　to　the　UML,　there　was　no　clear　leading(66)language.　Users　had　to　choose　from　among　many　similar　modeling　languages　with　minor　differences　in　overall(67)power.　Most　of　the　modeling　languages　shared　a　set　of　commonly　accepted　concepts　that　are　expressed　slightly　differently　in　various　languages.　This　lack　of(68)discouraged　new　users　from　entering　the　OO　market　and　from　doing　OO　modeling,　without　greatly　expanding　the　power　of　modeling.　Users　longed　for　the　industry　to　adopt　one,　or　a　very　few,　broadly　supported　modeling　languages　suitable　for(69)usage.

Some　Vendors　were　discouraged　from　entering　the　OO　modeling　area　because　of　the　need　to　support　many　similar,　but　slightly　different,　modeling　languages.　In　particular,　the　supply　of　add　on　tools　has　been　depressed　because　small　vendors　cannot　afford　to　support　many　different　formats　from　many　different(70)modeling　tools.　It　is　important　to　the　entire　OO　industry　to　encourage　broadly　based　tools　and　vendors,　as　well　as　niche　products　that　cater　to　the　needs　of　specialized　groups.

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