5英寸磁盘，最小磁道的直径为4厘米，最大磁道直径为8厘米，每分钟10000转，共有30记录面，每个记录面有8000个磁道，每条磁道上有511个扇区，每个扇区实际记录有600个字节，其中有效数据为512个字节。则这个磁盘存储器的有效存储容量是(1)GB，磁道密度是每毫米(2)条磁道。

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In　data　communication,　data　link　is　those　parts　of　two　data　terminal　equipments　that　are　controlled　by　a　protocol　along　with　the(71) data　circuit,　which　together　enable　data(72).　So-called　protocol　means,　in　short,　a　set　of　rules　that　determines　the　behavior.　of　functional　units　in　achieving　communication.Data　circuit,　however,　consists　of　a　pair　of(73) transmission　channels　that　provides　a　means　of　two-way　data　transmission.　Between　data　switching　exchanges,　the　data　circuit　may　or　may　not　include　data　circuit-terminating　equipment (DCE),　depending　on　the　type　of(74) used　at　the　data　switching　exchange.　Between　a　data　station　and　a　data　switching　exchange　or　data　concentrator,　the　data　circuit　includes　the　DCE　at　the　data　station　end,　and　may　include　equipment(75) to　a　DCE　at　the　data　switching　exchange　or　dam　concentrator　location.

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Calculator　is(66) for　performing　arithmetic　operations,　but　that　requires　human　intervention　to　alter　its　stored　program,　if　any,　and　to　initiate　each　operation　or　sequence　of　operations.　A　calculator　performs　some　of　the　functions　of　a　computer,　but　usually　operates　only　with　frequent　human　intervention.Microcomputer's　processing　unit　consists　of　one　or　more　microprocessors,　and　includes　storage　and　input-output(67).　Personal　computer　primarily　intended　for(68) use　by　an　individual.(69) computer　can　be　hand-carried　for　use　in　more　than　one　location.　Minicomputer　is　functionally　intermediate　between　a　microcomputer　and　a　mainframe.　And　supercomputer　has　the　highest　processing　speeds　available　at　a　given　time　for(70)　scientific　and　engineering　problems.