用户最关心的存储器的性能主要有(2)。关于常用的只读存储器ROM的正确描述是：(3)只能由生产厂家在生产芯片的过程中写入，用户无法改写。(4)允许用户写入一次，以后只能读出，不能改写。(5)不仅可以由用户写入，而且允许用紫外线擦除已经写入的内容。(6)可以直接用电信号按字节改写。

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(33)

The　data　station　usually　means　a(71)unit　that　provides　data　for　transmission,　that　accepts　transmitted　data,　and　that　performs　all　functions　necessary　for　communication　with　another　functional　unit.　Data　stations　may　be　divided　into　two　kinds,　the　primary　stations　and　the　secondary　stations,　(72)control　functions.In(73)data　link　control,　the　primary　station　is　the　data　station　that　supports　the　primary　control　functions　of　the　data　link,　generates　commands　to　be　transmitted,　and　interprets　received　responses.　Specific　responsibilities　assigned　to　the　primary　station　include　initialization　of　control　signal　interchange,　organization　of　data　flow　and　actions　regarding　error　control　and　error　recovery　functions.　The　secondary　station　executes　data　link　control　functions　as　(74)by　the　primary　station,　interprets　received　commands　and　(75) responses　to　be　transmitted.

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To　round　is　to　delete　or(66)one　or　more　of　the　least　significant　digits　in　a　positional(67)and　to,　or　not　to,　adjust　the　part　retained　in　accordance　with　some　specified　rule.　The　purpose　of　rounding　is　usually　to　limit　the　(68) of　the　numeral　or　to　reduce　the　number　of　characters　in　the　numeral,　or　to　do　both　these　things.The　most　common　arithmetic　forms　of　rounding　are　rounding　down,　rounding　up　and　rounding　off.　Rounding　down　is　defined　as　making　no　adjustment　to　the　part　of　the　numeral　that　is　retained.　Rounding　up　means　adjusting　the　part　of　the　numeral　that　is　retained　by　adding　1　to　the　least　significant　of　its　digits　and　executing　any　necessary　carries,　if　and　only　if　One　or　more　non-zero　digits　have　been　deleted.　Rounding　off　(69) adjusting　the　part　of　the　numeral　retained　by　adding　1　to　the　least　significant　of　its　digits　and　executing　any　necessary　carries,　if　and　only　if　the　most　significant　of　the　digits　deleted　was　equal　to　or　greater　than　half　the(70) of　its　digit　place.

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