MIT 6 033 - Intro to Computer Systems (10 pages)

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Intro to Computer Systems



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Intro to Computer Systems

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Pages:
10
School:
Massachusetts Institute of Technology
Course:
6 033 - Computer System Engineering
Computer System Engineering Documents
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L1 Intro to Computer Systems Complexity Robert Morris and Frans Kaashoek 6 033 Spring 2009 http web mit edu 6 033 http web mit edu 6 033 Schedule has all assignments Every meeting has preparation assignment First deliverable is due Tuesday Read the Therac paper for Friday Return sign up sheet at the end of lecture if you didn t do so yesterday We will post sections assignment tonight Example 6 033 Readings Therac 25 UNIX Ethernet End to End Arguments System R Emergent Property Example Ethernet All computers share single cable Goal is reliable delivery Listen before send to avoid collisions Will listen while send detect collisions Maximum cable length Minimum packet size Propagation of Effects Example L Cole 1969 WHO attempted to control malaria in North Borneo Sprayed villages with DDT Wiped out mosquitoes but Roaches collected DDT in tissue Lizards ate roaches and became slower Easy target for cats Cats didn t deal with DDT well and died Forest rats moved into villages Rats carried the bacillus for the plague WHO replaced malaria with the plague Galileo in 1638 To illustrate briefly I have sketched a bone whose natural length has been increased three times and whose thickness has been multiplied until for a correspondingly large animal it would perform the same function which the small bone performs for its small animal From the figures here shown you can see how out of proportion the enlarged bone appears Clearly then if one wishes to maintain in a great giant the same proportion of limb as that found in an ordinary man he must either find a harder and stronger material for making the bones or he must admit a diminution of strength in comparison with men of medium stature for if his height be increased inordinately he will fall and be crushed under his own weight Whereas if the size of a body be diminished the strength of that body is not diminished in the same proportion indeed the smaller the body the greater its relative strength Thus a small dog could probably carry on his back two or three dogs of his own size but I believe that a horse could not carry even one of his own size Dialog Concerning Two New Sciences 2 Day nd Incommensurate scaling Scaling a mouse into an elephant Volume O x3 where x is a linear measure Bone strength cross section O x2 Haldane On being the right size 1928 Scaling the Internet 39 sites in 1973 Total size of tables for shortest paths O n2 Scaling Ethernet s bit rate 10 mbit s min packet 64 bytes max cable 2 5 km 100 64 bytes 0 25 km 1 000 512 bytes 0 25 km 10 000 no shared cable Example more goals more complexity 1975 Unix kernel 10 500 lines of code 2008 Linux 2 6 24 line counts 85 000 430 000 490 000 710 000 1 000 000 4 000 000 7 800 000 processes sound drivers network protocols file systems different CPU architectures drivers Total Example interacting features more complexity Call Forwarding Call Number Delivery Blocking Automatic Call Back Itemized Billing CNDB ACB IB A B CF CF A C A calls B B is busy Once B is done B calls A A s number on appears on B s Class plan Next lecture computer systems are different Naming gluing modules together Client server enforced modularity Networks hard boundaries between modules Reliability and transactions handing failures Security handling malicious failures


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