Digital Logic - Wellesley College · 2018-10-24 · Digital Logic Microarchitecture Instruction Set...
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CS 240 in context Devices (transistors, etc.) Solid-State Physics Hardware H Digital Logic Microarchitecture Instruction Set Architecture Operating System Programming Language Compiler/Interpreter Program, Application, Algorithm Software How Computers Work 1 Security + Reliability Trickiest exploits & errors involve multiple layers, even hardware! Performance Memory: clever, imperfect abstraction. Tiny code changes, huge impact. Representation No representation without taxation. Representations have costs. Abstraction Do not start every project with transistors. Abstraction is beautiful and empowering, but real abstractions have leaks and wrinkles. These things matter more every day. Translation Between layers of abstraction. Structured computation. Big Ideas in CS, Systems, and beyond 2
Transcript of Digital Logic - Wellesley College · 2018-10-24 · Digital Logic Microarchitecture Instruction Set...
CS240incontext
Devices(transistors,etc.)
Solid-StatePhysics
Hardware
H
DigitalLogic
Microarchitecture
InstructionSetArchitecture
OperatingSystem
ProgrammingLanguage
Compiler/Interpreter
Program,Application,Algorithm
Softw
are
HowCom
putersW
ork1
Security+ReliabilityTrickiestexploits&errors
involvemultiplelayers, evenhardware!
PerformanceMemory:clever,imperfectabstraction.
Tinycodechanges,hugeimpact.
RepresentationNorepresentationwithouttaxation.
Representationshavecosts.
AbstractionDonotstarteveryprojectwithtransistors.Abstractionisbeautifulandempowering,
butrealabstractionshaveleaksandwrinkles.
Thesethingsmattermoreeveryday.
TranslationBetweenlayersofabstraction.
Structuredcomputation.
BigIdeasinCS,Systems,andbeyond2
Ariane 5Rocket,1996Explodedduetocastof64-bitfloating-pointnumberto16-bitsignednumber.Overflow.
1998MarsClimateOrbiterDisintegratedduetomismatchedunitsinLockheed-Martin/NASAsoftwarecomponents.
http://www.safetyresearch.net/blog/articles/toyota-unintended-acceleration-and-big-bowl-%E2%80%9Cspaghetti%E2%80%9D-code
Toyota"UnintendedAccelerationEvents"Oklahomajury:"SpaghettiCode"="recklessdisregard"
>10,000globalvariables81,514violationsofMISRA-Ccodingrules
Expect3minorbugs+1majorbugper30violations
Task/processmonitoringfailedtomonitortasks/processesMemorycorruption
(Wait,itwaswritteninC?!?!?!)
"...aModel787airplane thathasbeenpoweredcontinuouslyfor248dayscanloseallalternatingcurrent(AC)electricalpowerduetothegeneratorcontrolunits(GCUs)simultaneouslygoingintofailsafemode...Thisconditioniscausedbyasoftwarecounter internaltotheGCUsthatwilloverflow after248days ofcontinuouspower.WeareissuingthisADtopreventlossofallACelectricalpower,whichcouldresultinlossofcontroloftheairplane."--FAA,April2015
https://xkcd.com/571/
Howcouldweimprovecomputersystems?Security
EfficiencySpeedSpaceProgrammerCost,availability
Whatasimplephonecandoforpeople:https://opendatakit.org/about/deployments/
Energy,materialsA fewoftheimpactsweusuallydon'tsee:http://www.nytimes.com/2015/06/07/magazine/making-and-unmaking-the-digital-world.html?_r=0
Reliability
…
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(image:CCBY-SA,©WilliamHook) (image:CCBY-NC-SA,©jntolva)
(image:CCBY-SA,©KentaroIEMOTO@Tokyo)
SkillsforThinkingandProgramming
FewofyouwillbuildnewHW,OS,compiler,but…1. Effectiveprogrammersunderstandtheirtoolsandsystems.2. Theskillsandideasyoulearnhereapplyeverywhere.
Reasonaboutcomputationalmodels,translation.
Debugforcorrectnessandperformance(withtoolstohelp).
Assesscostsandlimitsofrepresentations.
"Figureitout"viadocumentation,experiments,criticalthinking.
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CS240:Computer Systems/Organization
CS3??:OperatingSystems
CS251:ProgrammingLanguages
CS301:CompilersandRuntimeSystems
CS342:ComputerSecurity
CS3??:Computer Architecture
CS249:ScientificandParallelComputing
Research
CS242:Computer Networks
Foundations
CS349:Distributed Computing
CS304:Databases withWebInterfaces
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