CS120: Lecture 1

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CS120 Lecture 1

• MP Johnson
• Hunter College
• mpjohnson_at_gmail.com

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agenda

• Admin
• Syllabus
• Survey
• Data, storage, representation

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admin

• Sessions 948-1126am / 1136-114pm HW 224
• Class page
• Email
• Text
• OHs tba
• Grading
• Hw (written, prog., labs) O(6) 45
• Exams 20 25
• Class partic/quizzes 10
• Start or end of class
• Attendance is required 80

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Core Class topics

• 1 Breadth-first tour of CS
• 2 Data
• storage
• Representation of knowledge)
• Compression (JPG, MP3)
• 3 How computers work
• Machines
• networks, Internet, OS
• HTML
• FTP, SSH
• Algorithms good ones?
• Programming / SE / data structures

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Advanced/optional

• AI
• Hardware
• Crypto
• Unsolvable problems
• Search Engines
• Social/political issues?
• Other topics?
• Some parts of class will be challenging
• Many will be applied/topical read Slashdot/Digg

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Survey

1. Name
2. Email (clearly!!)
3. Grade-level
4. Major
5. Why taking class
6. Topics youre most interested in

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Q What are comps?

• A machines that compute
• Q compute what?
• A the output of some algorithm
• Alg list of instructions / recipe
• Abstract but unambiguous (how?)
• Much more later
• Egs long division algorithm, gcd, sorting

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Long (pre)history

• Abacus (3000BC) just storage
• Pascal (1600s) addition
• Leibniz (1600s/1700s) math
• Babbage Diff. gin (1800s) math
• Babbage An. Gin punched cards
• All these were mechanical (gears, etc.)
• Difficult to make reliable fast cheap

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20th C electronics

• Circuits, transistors, etc.
• Mach 1, ENIAC, UNIVAC (1940s) - room-sized
• Since then just miniaturization
• Mainframes ? supercomps, minis ? PCs (micros)
  early 80s on
• All essentially same
• Run many programs (v. arcade machine)
• These programs impl. Algs (tho in diff. langs)
• They store, rep, use data

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Today data

• CS abstraction reduction
• thats so reductive
• In CS, all data is numbers,
• All numbers are bits (0/1) / bools (F/T)
• Bit binary digit
• boolean George Boole (1800s)

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Bool logic/algebra

• Vals F, T
• Ops and, or, xor, not
• Draw truth tables
• Xor intuit soup or sald
• Can write exprs
• Exprs can nest

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Bool expr eg

• Suppose A empl A is working, B, C
• Suppose want should always be exactly one empl
  working
• Q If we only know bool logic, how to test?
• Q how to write a program for this in bool
  logic?
• (A B C)
• (A xor B)
• (A B C)

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Q How to compute/eval this?

• We now understand bool ops, so we could perform
  each op ourselves
• A gp of female workers in WWII were called
  computers
• Bad too slow, error-prone
• Funda strength of comps can do some (v. simple)
  things v. fast

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strategy

• Dont create a special machine to comp whole
  expr/function/program
• Do create a little machine for each component,
  then combine
• Forget about software for now!
• How? First, bool ops ? gates

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gates
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Gates ? elec circuit

• No one of these is v. interesting
• But two big insights
• Can create an implement gate electronically
• 0/1 ? low/high current
• Gates can be combined to produce powerful
  computations / representations
• ? electronic circuits / chips
• Draw circuits for each expr
• Of course, want software (non-kickable)
• For that we need a compiler

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Circuits as memory
Reading for next week wiki entries on boolean
logic and twos complete (through section 2 only)

• Flipflop special circuit that can store data
• 1 bit per FF

To store, send pulse in top or bottom (0 is
ddf) Go through