CS 501: Software EngineeringAdministrationThe Y2K Problem: Saving MemorySlide 4Where's the Problem?Find Every Occurrence ...Slide 7Social ConsequencesOrganizational ProceduresY2K ValidationTechnical StrategiesNew BugsIs all the Money Going to Y2K?ProfiteeringFinal Thoughts on Y2K1CS 501 Spring 2002CS 501: Software EngineeringLecture 25Maintenance and Legacy Systems2CS 501 Spring 2002Administration3CS 501 Spring 2002The Y2K Problem: Saving Memory• In 1967 memory cost $1 per byte The Air Force used single digit dates• If 2-digit dates saved 1% of memory... savings over 20 years $16 to $24 million per gigabyte4CS 501 Spring 2002The Y2K Problem: Saving Memory• By 1980s, memory was much cheaper, but 2-digit dates were standard. Why incur the cost of changing standards?1970 The mortgage industry 1990 The Social Security Industrymoved towards 4-digit dates • On January 1, 2000 2-digit dates stopped working!5CS 501 Spring 2002Where's the Problem?• A simple bug:dates of the form 19xx have been encoded xx• A simple fix:find every occurrence of the bugmodify the coderecompileWhere's the problem?6CS 501 Spring 2002Find Every Occurrence ...• What computers do we use?data processingcontrolembedded systemspersonal devices• What programs do they run?in-house development packages and librariesfirmware, microcode, hardwareWho wrote this program?Where is the source code?7CS 501 Spring 2002Where's the Problem?Computers fail everyday. What's special about this bug?• What if they all fail at the same time?• What if we lose telephone, electricity, radio, etc.?• Traffic signals, elevators, The greatest worry was uncertainty.8CS 501 Spring 2002Social ConsequencesWorry creates its own problems:• Wal-Mart forecast lower profits in Q1 2000• Legislation to limit law suits• Opportunities for computer fraud and sabotage9CS 501 Spring 2002Organizational Procedures• Ostrich=> do nothing=> buy insurance• Bureaucratic=> fill in forms that programs are compliant• Subcontract=> hire Y2K specialists• Do it yourself=> in-house computing department10CS 501 Spring 2002Y2K ValidationRequest from Library of Congress to confirm that our code is Y2K compliant: Our code is fine .... but it depends on ... which depends on ... Yes. Our code is fine.Request from DARPA to confirm that our code is Y2K compliant: It's been validated by another part of the US government Thank you!11CS 501 Spring 2002Technical Strategies• Replace noncompliant applications with compliant ones (e.g., new versions of packages)• Repair noncompliant applications (e.g., in-house applications)• Terminate noncompliant programs on an as-needed basis • Mask the data exchange between applications• Object code interception12CS 501 Spring 2002New BugsIf it's not broke don't fix it.• 10 billion lines of code checked (often automatically)• ??? 10 million new bugs introduced accidentally• ??? security holes, errors, etc. introduced accidentally or deliberately13CS 501 Spring 2002Is all the Money Going to Y2K?Y2K as a great excuse to have the computing budget increased:• Upgrade the operating system• Replace the old package• Sell something to your customersWhat boss will turn turn a request for Y2K funds?What systems administrators will not install Y2K upgrades?14CS 501 Spring 2002Profiteering• Buy gold, wood stoves, bottled water• Y2K specialists• Pundits, consultants, writers• Religious cranks15CS 501 Spring 2002Final Thoughts on Y2KWe create computer systems that are more complex than our understanding of them:• We over estimate our ability to validate systems• We under estimate our ability to adapt and respondSoftware engineering usually thinks of systems as independent.Will the long-term benefit of the Y2K problem be a greater understanding of how software systems interact with each other and with our social
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