Lectures 4 & 5notes
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This 5 page Class Notes was uploaded by Heather Perkins on Friday February 6, 2015. The Class Notes belongs to 13803 at University of Massachusetts taught by William Verts in Spring2015. Since its upload, it has received 56 views.
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Date Created: 02/06/15
Gates and Truth Tables Binary addition addition in 1 base should give the same answer as addition in another base 0 We build computers in binary Logic 0 When is this sentence true 0 I am going to the store and going to the beachquot 0 Clause A store 0 Clause B beach 0 Either may be independently true or false But when is it true Only when both clauses are true 0 Truth table is a tabular way of describing all possible behaviors for a binary system 0 True 1 and False O o of rows is a power of 2 number of inputs rows is 2N We can have more than 2 inputs but everything must be true open etc in order for it to be true 0 If we can describe the behavior of AND we can describe OR but there s a catch 0 OR is different in English than it is in computer logic XOR the exclusive or One or the other not either not both Logic almost always something else inclusive OR 0 General rules 0 AND output of and is true only if all inputs are true 1 0 OR if output is 1 any input is 1 If output is 0 all inputs are 0 o XOR the output is 1 if the inputs differ the output is 0 if the inputs are the same 0 NOle I am not going to the store Output is NOT what the input is Gates 0 A gate is o A mathematical abstraction for o A physical device that o Implements the function of a truth table NTOT AND LE DE Out httpwwwhomofaciensdetechnicsbasecircuitsIogic gatesennavionhtm The Internet and the Web 0 Web addresses httpwwwcsumasseduvertscoinleScoinleShtml 0 URL uniform resource locators 0 Protocol H39ITP Type of internet communication required One among many 0 http 0 ftp tenet Read from right to left Top level domain edu Network umass sub network cs Machine name www not all web addresses use www 0 Username verts Folder on site belonging to a particular user Notice the quottildequot character Not all urls need one 0 Folder path coinleS All web les are in a special folder called publichtm never shown as a part of url users may or may not create subfolders to publichtm to contain related les 0 Resource coinleShtml lf present last part of url The document le actually fetched Types of web les by extension html txt gifjpgpng What if the resource isn t speci ed 0 Going to assume you re looking for a default le called indexhtml or indexhtm Top level domains since other countries also use top level domains they ll combine country codes with domains edu com gov net org mil Basic networking you can connect your computer to a network through an Ethernet cable or you can use wireless wi Client server model computerbrowser is the client your remote computer containing desired resource is the server there may be computers in between each resource is requested separately so no single client can dominate the server requests from one client are interleaved with requests from other clients Packets resource les split into packets 0 packets from one resource are interleaved with packets from other resources 0 intermediate machines send packets to machines quotcloserquot to their desired destinations Packets may follow different paths and arrive out of order depending on traf c or network damage Packet Sniffers Legitimate programs that examine packets to make certain they re constructed correctly compromised packet sniffers may watch for sensitive information ssn passwords ccs etc 0 Treat email as a postcard Encrypt IP Addresses unique identi er for a machine 0 used by routers to guide packets va4 four bytes 32 bits 0 43x109 4 billion addresses We ran out in 2011 o va6 eight two byte words 128 bits 0 34x1038 addresses 0 Deployed but still not widely used DNS amp IP addresses 0 DNS maps host names from URLs into numeric IP addresses 0 Could type in IP address directly Building web pages 0 Many web design tools exist 0 Adobe dreamweaver 0 Microsoft expression web 0 We use text editors in this class 0 Most web pages with active content use an html code 0 HTML tags are items inside angle brackets HTML tags come in two forms 0 Singleton tag ltTAGgt or ltTAG gt o Enclosing tag ltTAGgt or ltTAGgt Singleton or opening tags may contain optional attributes What doesn t matter 0 White space blanks tabs new lines etc Capitalization with a few exceptions Indentation Dr B indents 4 spaces per level
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