动态存储器芯片的正常访问周期为60us，其中，输入行地址和列地址分别需要20ns。如果行地址不变，只改变列地址，则可以节省输入行地址的时间。对于一个容量为64MB的芯片，全部存储单元都访问一遍至少需要(3)s。

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Network　managers　have　long　awaited　practical　voice-over-IP(VOIP)solutions.　VOIP　promises(71)network　management　and　decreases　costs　by(72)a　company's　telephony　and　data　infrastructures　into　one　network.　And　a　VOIP　solution　implemented　at　a　company'　s　head　-quarters　with　far　-reaching　branch　offices　can(73)tremendous　amounts　of(74)in　long　distance　phone　bills,　provided　that　solution　delivers　POTS　-like　voice(75)over　the　Internet.

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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 propagaterouting information.

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

(70)is an identifier of a web page.

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