pete > courses > CS 202 Spring 24 > Lecture 01: Introduction

Lecture 01: Introduction

Goals

introductions

administrivia

poll: how many are not officially signed up?

course website: go/cs202

department/major information: go/cswiki

masks

grading

reference materials (ie, no required texts)

notes online

goals on the board: both lecture outline and highlight things you should be able to do after this lecture and reviewing notes

drop-in help sessions TBA

this class is all about abstraction

what is abstraction?

abstraction is hiding details

lets us avoid worrying about HOW things work and just trust that they DO

for instance…

they’re magic!

this class is about dispelling that magic (sorry)

why is abstraction important?

we can only keep so much in our heads at any one time

filtering out the wee details lets us solve big problems

BUT

sometimes the wee details bite the higher abstraction level in the ass

many security problems occur precisely because of this

(examples later in the course)

also but, sometimes the higher level can take advantage of things going on at the lower level

what do I mean by ``higher level’’?

the more abstract

the less specifically defined

you’ve already dealt with this when writing your own functions

you’ve wrapped up the gory details of some operation into a function, the specific details of which are irrelevant to whichever code calls said function

in fact, ``abstraction’’ was the original, historical term for what we now call functions (Alonzo Church, 1936)

in this regard, Python is ``high level’’

Python itself is implemented in the C programming language

which compiles down to an assembly language

which is translated into machine code

which drives a finite state machine

which is implemented using sequential logic

which is composed of storage elements and combinational logic

both of which are built from logic gates

which are themselves built from transistors

which work because physics

which really IS magic

(the hierarchy with other languages, eg Java, at the top is remarkably similar)

we’re going to dig into and play with all the layers of this pillar

as well as some other offshoots that make computers work

and others that make computers fast (optimization)

you will build things at each level to understand how they work

there are (at least) two ways we can go about this

we can start from the top and drill down

or we can start from the bottom and build up

I prefer the latter approach

gives you practice building things

so when we get to, say, sequential logic

you’re going to have a toolbox of storage elements and combinational logic

and you’re going to use those to build sequential logic

this process of learning what’s in your toolbox and working with it is endemic to developing with computers

you get a new job, they’re going to have their own preferences of which languages to use (you may not get a choice!)

you get a new hobby, maybe the popular languages are new to you

plus ca change, plus ca meme chose

a big part of the reason to go bottom-up is to give you practice with the pattern of learning a toolbox and applying it

last caveat before we start to dig in: exceptions to EVERYTHING

simple LED circuit, physically

simple LED circuit, drawn

simple LED circuit, simulated: basic_led.circ

the latter is an abstraction of the former

it ignores details

these details may or may not be relevant (depends on your intent)

what do we lose?

notion of voltage (and hence the resistor)

ground isn’t even connected!

no ``circuit’’ in the sense that the current can’t flow from + to -

no assignments on real-life circuits

they are BELOW the abstraction level we care about in this class

if you’re interested in this stuff, though…

Definitions

The following definitions introduced in this lecture are fair-game for future quizzes. You will be expected to give the exact definition as provided in these lecture notes.

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