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1、操作系统作业1_1翻译《whatisanoperatingsystem》1.1WHATISANOPERATINGSYSTEM?Mostcomputerusershavehadsomeexperiencewithanoperatingsystem,butitisdifficulttopindownpreciselywhatanoperatingsystemis.Partoftheproblemisthatoperatingsystemsperformtwobasicallyunrelatedfunctions,extendingthemachi
2、neandmanagingresources,anddependingonwhoisdoingthetalking,youhearmostlyaboutonefunctionortheother.Letusnowlookatboth."大多数计算机用户有一些作业系统的经验，但很难牵制正是一个操作系统。这个问题的部分原因是，作业系统执行两个基本无关的功能，延长机器和管理资源，以及是谁在说话，你听到的多半是一个函数或其他而定。现在让我们看看两者。"1.1.1TheOperatingSystemasanExtendedMachineAsmentio
3、nedearlier,thearchitecture(instructionset,memoryorganization,I/O,andbusstructure)ofmostcomputersatthemachinelanguagelevelisprimitiveandawkwardtoprogram,especiallyforinput/output.Tomakethispointmoreconcrete,letusbrieflylookathowfloppydiskI/OisdoneusingtheNECPD765compatibleco
4、ntrollerchipsusedonmostIntel-basedpersonalcomputers.如前所述，该架构（指令集，内存组织，我/O和总线结构的大多数计算机）在机器语言水平是原始和笨拙的方案，特别是输入/输出。为了使这一点更具体，让我们简单地看一看软盘磁盘I/O是使用NECPD765进行兼容控制器在大多数基于英特尔芯片的个人电脑使用的芯片。(Throughoutthisbookwewillusetheterms“floppydisk”and“diskette”interchangeably.)ThePD765has16comma
5、nds,eachspecifiedbyloadingbetween1and9bytesintoadeviceregister.Thesecommandsareforreadingandwritingdata,movingthediskarm,andformattingtracks,aswellasinitializing,sensing,resetting,andrecalibratingthecontrollerandthedrives.（在本书中我们将使用术语“软盘”和“软盘”互换。）的PD765有16个命令，由1至9载入字节每个指定到一
6、个设备寄存器。这些命令用于读取和写入数据，移动磁盘的手臂，和格式曲目，以及初始化，传感，复位，并重新调整了控制器和驱动器。Themostbasiccommandsarereadandwrite,eachofwhichrequires13parameters,packedinto9bytes.Theseparametersspecifysuchitemsastheaddressofthediskblocktoberead,thenumberofsectorspertrack,therecordingmodeusedonthephysicalme
7、dium,theintersectorgapspacing,andwhattodowithadeleted-data-address-mark.Ifyoudonotunderstandthismumbojumbo,donotworry;thatispreciselythepoint—itisratheresoteric.Whentheoperationiscompleted,thecontrollerchipreturns23statusanderrorfieldspackedinto7bytes.Asifthiswerenotenough,
8、thefloppydiskprogrammermustalsobeconstantlyawareofwhetherthemotorisonoroff.Ifthemo
