计算机控制器的设计有两种方案：组合逻辑方案和微程序方案，微程序方案对指令的扩充、修改，调试、维护都方便，因而得到广泛应用。计算机中微程序放在(6)中。

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Software　design　is　a(71)process　.It　requires　a　certain(72)of　flair　on　the　part　of　the　designer.　Design　can　not　be　learned　from　a　book　.It　must　be　practiced　and　learnt　by　experience　and　study　of　existing　systems　.A　well(73)software　system　is　straightforward　to　implement　and　maintain　,easily(74)and　reliable　.Badly(73)software　systems　,although　they　may　work　are(75)to　be　expensive　to　maintain　,difficult　to　test　and　unreliable.

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(66)is a protocol that a host uses to inform. a router when it joins or leaves an Internet multicast group.

(67)is an error detection code that most data conlmunication networks use.

(68)is an interior gateway protocol that uses a distance vector algorithm to propagate routing information.

(69)is a transfer mode in which all types of information are organized into fixed form. cells on an asynchronous or nonperiodic basis over a range of media.

(70)is an identifier of a web page.