Operating Systems COT 4600 – Fall 2009Lecture 3NamesNames and fundamental abstractionsComputers a distinct species of complex systemsAnalog, digital, and hybrid systemsComputers are controlled by softwareExponential growth of computersCoping with complexity of computer systemsIteration – design principlesCurbing complexityCritical elements of information revolution!Slide 13The relation between homo sapiens and the computersResource sharing and complexitySlide 16Slide 17Operating Systems COT 4600 – Fall 2009Dan C. MarinescuOffice: HEC 439 BOffice hours: W, F 3:00-4:00 PMLecture 1 2Last timeComputer SystemsToday:NamesComputer Systems versus Other SystemsCoping with Computer System ComplexityNext timeThe projectHomework 1 due Thursday, September 3, 2009Lecture 3Lecture 1 3NamesModularity along with abstraction, layering, and hierarchy allow a designer to cope with complexity;Names and addresses  provide the means to connect modules. A system  a bunch of resources, glued together with namesNaming allows the designer to:Delay the implementation of some modules; use dummy onesReplace an implementation with another one.Binding choosing an implementation for a moduleDelayed binding; use a place holder.Lecture 1 4Names and fundamental abstractionsThe fundamental abstractions1. Storage  mem, disk, data struct, File Systems, disk arrays2. Interpreters  cpu, programming language e.g. java VM3. Communication wire, Ethernet rely on names.Naming:FlatHierarchicalLecture 1 5Computers a distinct species of complex systemsThe complexity of computer systems not limited by the laws of physics  distant bounds on compositionDigital systems are noise-free.The hardware is controlled by softwareThe rate of change unprecedentedThe cost of digital hardware has dropped in average 30% per year for the past 35 yearsLecture 1 6Analog, digital, and hybrid systemsAnalog systems:the noise from individual components accumulate and the number of components is limitedDigital systems: are noise-freethe number of components is not limitedregeneration  restoration of digital signal levelsstatic discipline the range of the analog values a device accepts for each input digital value should be wider than the range of analog output valuesdigital components could fail but big mistakes are easier to detect than small ones!!Hybrid systems  e.g., quantum computers and quantum communication systemsLecture 1 7Computers are controlled by softwareComposition of hardware limited by laws of physics.Composition of software is not physically constrained; software packages of 107 lines of code existAbstractions hide the implementation beneath module interfaces and allow the creation of complex softwaremodification of the modulesAbstractions can be leaky. Example, representation of integers, floating point numbers.Lecture 1 8Exponential growth of computersUnprecedented: when a system is ready to be released it may already be obsolete. when one of the parameters of a system changes by a factor of 2 other components must be drastically altered due to the incommensurate scaling. 10  the systems must be redesigned; E.g.; balance CPU, memory, and I/O bandwidth;does not give pause to developers to learn lessons from existing systemsfind and correct all errorsnegatively affects “human engineering”  ability to build reliable and user-friendly systemsthe legal and social frameworks are not readyLecture 1 9Coping with complexity of computer systemsModularity, abstraction, layering, and hierarchy are necessary but not sufficient.An additional technique  iterationIterationDesign increasingly more complex functionality in the systemTest the system at each stage of the iteration to convince yourself that the design is soundEasier to make changes during the design processLecture 1 10Iteration – design principlesMake it easy to changethe simplest version must accommodate all changes required by successive versionsdo not deviate from the original design rationalethink carefully about modularity  it is very hard to change it.Take small steps; rebuild the system every day, to discover design flaws and errors. Ask others to test it.Don’t rush to implementation. Think hard before starting to program.Use feedback judiciously use alpha and beta versionsdo not be overconfident from an early successStudy failures  understand that complex systems fail for complex reasons.Lecture 1 11Curbing complexityIn absence of physical laws curb the complexity by good judgment. Easier said than done because:tempted to add new features than in the previous generationcompetitors have already incorporated the new features the features seem easy to implementthe technology has improvedhuman behavior: arrogance, pride, overconfidence…Lecture 1 12Critical elements of information revolution!Lecture 1 13Lecture 1 14The relation between homo sapiens and the computersThe feelings of the homo sapiens:HateFrustrationLack of understandingThe Operating System  A program to “domesticate” the computer.Transforms a “bare machine” into a “user machine”Controls and facilitates access to computing resources; optimizes the use of resources.The relation went through several stages:Many-to-oneOne-to-oneMany-to-manyPeer-to-peerLecture 1 15Resource sharing and complexity A main function of the OS is resource sharing.Sharing computer resources went through several stages with different levels of complexity:Many-to-oneOne-to-oneMany-to-manyPeer-to-peerLecture 1 16Lecture 1