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Computer Science
Computer Science 1011A/B
Laura Reid

CS1011 Midterm Review Why has the Internet succeeded? 1. Size 2. Speed 3. Reliability 4. Security “Moore’s Law” (Gordon Moore) - The amount of information that a computer can store for the same price has been doubling every couple of years, since computers were invented RAM= random access memory  the block of memory that the computer can access very quickly In networks… - Strings = “edges” - Knots = “nodes” - Nodes = computers, Edges = cables, wireless transmission, satellite links - Data is sent bit by bit over edges ArpaNet in 1971… 18 nodes (computers), 22 edges (land-based communication cables) - Internet traffic carried over by optical fiber cables - Messages travel at the speed of light The Alexandria accidents… - Later Jan/early Feb 2008 - Accidents cut some of the underwater cables linking Europe and Asia - Possibly cut my ship’s anchor - Internet capacity reduced by 75% Mombasa accident… - Feb 2012 - Ship’s anchor cut a cable by The East African Marine Systems (TEAMS) - Internet traffic to Kenya, Rwanda, Burundi, Tanzania, Ethiopia, and Southern Sudan slowed by 20% IP address = Internet Protocol - 4 numbers with dots in between them - Each number between 0 and 255 inclusive Domain Name Servers = DNS - Correspondence between symbolic and numeric addresses held by special Internet computers Router: computer customized to quickly route messages from one machine to another on the internet  often has many cables going in and out  routers often don’t have numeric IP addresses of their own 1940s nd - 2 world war: scientists wanted to replace the human effort it took to collect information/calculations. Women were considered the original “human computers” and it was their job to be a “computer” (they would spend their days collecting info) - First machines called “electronic computers” 1950s - Computers were pretty well established for defense calculations. Scientists and government started using them as well. They were expensive and very large in size. - Big businesses start using computers to process general data (“data processing”) Late 1950s - Computer took up a whole room - Computer input via punched cards (cardboard cards with holes punched in them) - Only one program could be running on a computer at one time 1960s - Timesharing developed at MIT around 1963 o Allowed more than one program to run at the same time o Fernando Corbato - Many people can be using a computer at the same time o One person’s program runs while other people sit and think ARPA = Advanced Research Projects Agency - J.C.R. Licklider joins US Department of Defense - Paul Baran (RAND Corporation) commissioned by US Air Force to study how to set up a network that would survive a nuclear attack Baran made two observations: 1. Distributed networks are best There were 3 designs of networks he talked about: centralized networks (one central node), decentralized networks (the middle can be cut into two or more pieces by taking out nodes), and distributed networks (still in one piece even if several nodes are taken out) - The distributed network is the most robust because it defies the loss of the whole network 2. Packet switching is best In order to allow for computer and communications equipment to easily transfer blocks, it was best to standardize the size of the block. If a message is longer than the standard size of a block: break it up into smaller blocks, label each block with a serial number, send each block separately, the receiver reassembles the blocks. This process came to be called "packet switching", and the computers that can route messages to more than one another are called "Switches." - Rand corporation published Baran’s reports - Packet switching networks accepted as “best solution” - Several research projects connect computers to each other o Some of the most influential funded by ARPA The ARPANet - Started in 1969 with 4 nodes (UCLA, SRI, UCSB, Uni of Utah) - By 1971 had 18 nodes - Compatibility problem: computers on a network may be made by different manufacturers o Each different computer would need different ways of sending messages - Compatibility solution: standardize the format of messages o Each message was translated by IMPs (Interface message processors) - ARPA funded a research project to integrate the different networks o Developed TCP (transmission Control Protocol) o Forerunner of IP (internet protocol) - “Father of the Internet” = Cerf and Kahn - The Internet was created by a combination of contributions from a number of different people/groups 1970s and 1980s - IP (Internetworking protocol) split off from TCP - Computers using IP or TCP started to be called “The Internet” - DNS (Domain name servers) were introduced - Usenet (Unix users’ network) starts o Writer writes message on one Unix computer, message automatically forwarded to all other computers on Usenet, messages usually forwarded using phone lines 1990s - FTP (File Transfer Protocol) The World Wide Web - Tim Berners-Lee announces the World Wide Web on the Usenet discussion group system - The first browser was not great, then came Mosaic, which was a more developed browser similar to the ones we use today - URL = uniform resource locators - HTML (hyper text markup language) - HTML allowed for images to be embedded on web pages - WiFi communication released by IEEE (Institute of electrical and electronic engineers) - 1998—Google founded - 1999—Napster (peer-to-peer file sharing) released - WinTel (platform) dominated in 1990s-2000s - Google Android machines have captured a huge share of the market (nowadays) - Internet traffic to/from cellphones and laptops has surpassed traffic to/from desktop computers Bits - A bit is a thing that can have one of two values: 0 or 1 - Short for “binary digit” - General rule for Bit patterns: there are 2 possible patterns of n bits - In order to represent k different things, we need at least n bits, where n is the n smallest number such that 2 ≥ k - 1/2/4/8/16/32/64/128/256 - The 2 bit patterns of length n are interpreted as the numbers 0 to 2 – 1 n Bytes - Sequence of 8 bits - Usually the byte is the smallest unit of memory stored or transmitted Files - The contents = data o Always a sequence of bytes, - The wrapping = metadata o File name, date last modified, access permissions ASCII - American standard code for information interchange - Finalized by
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