Slide 1Lecture 6 – Tuesday, February 1, 2011Names and the three basic abstractionsSlide 4MemorySlide 6Slide 7RAID 3 and 4RAID 5 and 6Slide 10InterpretersAn abstract interpreterSlide 13Slide 14Slide 15COT 4600 Operating Systems Spring 2011Dan C. MarinescuOffice: HEC 304Office hours: Tu-Th 5:00 – 6:00 PMLast time: Complexity of Computer SystemsIterationNames and The Basic AbstractionsToday:Discussion of “Hints for Computer Systems Design” by Butler Lampson. Basic AbstractionsMemory. Interpreters.Communication links.Next timeNaming; Use by: value/name; Binding and indirectionGeneric naming modelPractical design of naming scheme; Contexts, Name overloadingLecture 6 – Tuesday, February 1, 20112Lecture 6Lecture 63Names and the three basic abstractionsMemory  stores named objects write(name, value) value  READ(name)file system: /dcm/classes/Fall09/Lectures/Lecture5.ppt Interpreters  manipulates named objects machine instructions ADD R1,R2modules  Variables call sort(table) Communication Links connect named objects HTTP protocol used by the Web and file systems Host: boticelli.cs.ucf.edu put /dcm/classes/Spring11/Lectures/Lecture6.ppt get /dcm/classes/Spring11/Lectures/Lecture6.ppt 3Lecture 644Lecture 65MemoryHardware memory:DevicesRAM (Random Access Memory) chipFlash memory  non-volatile memory that can be erased and reprogrammedMagnetic tapeMagnetic DiskCD and DVDSystemsRAIDFile systemsDBMS (Data Base management Systems)5Lecture 666Lecture 6 77Lecture 6 8RAID 3 and 4Raid 3 Striped set with dedicated parity or bit interleaved parity or byte level parity.Raid 4  improves reliability, it adds error correction8Lecture 6 9RAID 5 and 6Raid 5  striped disks with parity combines three or more disks to protect data against loss of any one disk. The storage capacity of the array is reduced by one diskRaid 6  striped disks with dual parity combines four or more disks to protect against loss of any two disks. Makes larger RAID groups more practical. Large-capacity drives lengthen the time needed to recover from the failure of a single drive. Single parity RAID levels are vulnerable to data loss until the failed drive is rebuilt: the larger the drive, the longer the rebuild will take. Dual parity gives time to rebuild the array without the data being at risk if a (single) additional drive fails before the rebuild is complete.9Lecture 6 1010Figure 2.3 from textbookLecture 6 11InterpretersThe active elements of a computer systemDiverse Hardware  Processor, Disk Controller, Display controllerSoftware  script language: Javascropt, Pearl, Pythontext processing systems: Latex, Tex, Word browser : Safari, Google Chrome,ThunderbirdAll share three major abstractions/components:Instruction reference  tells the system where to find the next instructionRepertoire  the set of actions (instructions) the interpreter is able to performEnvironment reference  tells the interpreter where to find the its environment, the state in which it should be to execute the next instruction11Lecture 6 12An abstract interpreter The three elements allow us to describe the functioning of an interpreter regardless of its physical realization.Interrupt  mechanism allowing an interpreter to deal with the transfer of control. Once an instruction is executed the control is passed to an interrupt handler which may change the environment for the next instruction.More than a single interpreter may be present. 12Lecture 6 1313Figure 2.5 from the textbookLecture 6 1414Figure 2.6 from the textbookLecture 6 1515Figure 2.7 from the