From mechanical calculators to computers

• A computer: http://makezine.com/projects/make-20/marble-adding-machine/
• Not a computer https://www.youtube.com/watch?feature=player_detailpage&v=wQGn4wTIFs4#t=50

Neither a computer...

The first programmable computer was the Analytical Engine designed by Charles Babbage.

It combined the Jacquard Loom with Babbage's Difference Engine

Jacquard Loom and

punch cards

Difference Engine

http://www.computerhistory.org/babbage/

A Computer

• Stores states (data/computation)
• Performs operations
• Is programmable

The electronic computer

• Essentially a miniaturization of the mechanical computer
• Memory of states often stored indirectly (not as part of the "mechanism")

Memory

• Faster is usually more expensive
• Dynamic (can be changed unlike to punch cards)
• Often fast memory is used for computation and larger small memory is used for long term storage
• Memory paging
• e.g. RAM (Random Access Memory)

Storage

• Slow but large
• Dynamic or static

Mercury Delay Lines

Acoustic Delay Lines

Magnetic Drum Memory

There are 10 types of people:

Those who understand binary and those who don't.

Binary

• 0001 => 1
• 0010 => 2
• 0011 => 3
• 0100 => 4
• 0101 => 5

Bits and binary

• In computing each binary digit is called a bit
• 8 bits make up one byte
• The number of possible combinations for N bits is 2^N
• i.e. that is the maximum number of states or values that can be represented with those bits.

Boolean Algebra

001 AND 111 = 001

010 OR 110 = 110

NOT 011 = 100

Binary numbers

• Just two digits
• To represent all information
• Easy to build circuitry to detect two states
• (Harder to detect multiple states)
• A bit is a "column" to store binary digits
• Endianness refers to whether the first digit is the highest or lowest valued digit

Hexadecimal

• Base 16
• Digits from 0 to F
• Each digit corresponds to 4 bits, 2 digits make a byte
• Often used to represent bytes in a concise way

Encoding information

• Bacon's cypher
• Punch cards (as in the Jacquard loom)

Binary encoding

• Numbers:
  • Integers - signed and unsigned
  • Floating point numbers
• Letters (ASCII codes): http://en.wikipedia.org/wiki/ASCII
• Color (#FF0000)
• Any data (by just adding more bits):
  • http://en.wikipedia.org/wiki/Barcode
  • This document!

Integers

• Unsigned integers can map directly to base 2 numbers
• Signed integers can be done in different ways
  • use 1 bit for sign
  • two's complement (the negative numbers count down from the maximum unsigned integer). Can result in more efficent basic calculations.

Programming statements

• Assignments and Expressions
• Conditional branching
• Loops

Intro to Python