Understandability.
Evolution of data transmission and storage.
Spoken word - stories and fables.
Low density - 100 to 200 words/minute. ( up to 400 - auctioneers )
Supports complexity +
Simile, metaphor, allegory, parables.
Fairly corruptible -
Game of telephone. (transmission over time)
Transmission over distance - messenger.
Small number of messages.
Universally shared skill within a community.
Often requires translation between communities.
Permanence +/-
Oral tradition - myths.
Written word
Fairly durable depending choice of media +
Supports complexity +
Low density -
Fairly corruption resistant +
physical +/-
clay tablets vs. paper.
data
Language translation, age of language. -
Required training - both reading and writing.
Rosetta stone
Pre-Gutenberg printing, required hand copying.
Transmission over distance (before modern technology)
Single messenger can carry multiple letters. Mailman and service.
Converting human knowledge to digital storage for communication, analysis,
and archiving.
Data encoding - the process of converting data to a standardized format based
on an agreed upon algorithm.
"In communications and information processing, code (encoding) is a
system of rules to convert information - such as a letter, word, sound,
image, or gesture - into another form or representation, sometimes shortened
or secret, for communication through a communication channel or storage in
a storage medium.
An early example is the invention of language, which enabled a person, through
speech, to communicate what he or she saw, heard, felt, or thought to others.
But speech limits the range of communication to the distance a voice can carry,
and limits the audience to those present when the speech is uttered.
The invention of writing, which converted spoken language into visual symbols,
extended the range of communication across space and time."
From : en.wikipedia.org/wiki/Code
Character encoding
Data storage
Punched tape 1725
Used to control the thread location on looms. ~ 1725
Warp and weft
Player piano ~ 1842
Mechanized telegram ~ 1846 (first attempt)
Preparation, storage, and transmission ~ 1857
Used to control automated system for producing type for typesetting. ~ 1880
Modern version of tape.
Image source : wikipedia punch tape
Can be viewed as an early form of binary discrete storage.
Presence or absence of punch in particular column.
Fairly low density
Modern tape made with Mylar, very durable.
Data not 'human' but visually readable if format understood.
Repairable with some effort.
Difficult to directly alter.
However, easy to deliberately destroy for security - shred.
Punch card
(Modularized tape)
Jacquard loom (1804)
Image source : wikipedia Jacquard loom
Joseph Marie Jacquard strung punch cards together to make 'tape'
Modular - each card is a specific pattern or algorithm.
Acts almost like an 'object' or 'subroutine'.
Easy to replace bad card.
Easy to add/alter/rearrange cards in sequence.
Human readable if encoding known.
Image source : wikipedia punch card
Fairly fragile but choice of material may improve this.
Fairly low density.
May need sequencing information which may add cost.
Punch card use for data processing continued until the mid 1980's when
magnetic storage superseded it.
Data transmission.
Bugle calls.
Set of predefined tunes that can clearly be heard in a battle situation.
Semaphore code - 2 flags, 8 positions. 1800's Strictly visual.
Requires lit wands at night.
wikipedia : flag semaphore
Image source : wikipedia semaphore
30 recognized flag positioning pairs, some pairs have dual meanings.
Used to code alphanumeric characters.
Also uses some motion or repeated patterns to signal special conditions.
Japanese adapted for their symbolic language, many 'characters'
requiring a pair of flag displays for each character.
Morse code (international) - dot, dash, and spaces (not binary). ~ 1836
Initially, used to transmit numbers.
Later, expanded to include alpha-characters. (1840 Alfred Vail)
Image source : wikipedia Morse code
Standardized electrical signaling. Audio, visual.
Character - A-Z 0-9
Dot/dash count varies between characters - 1-5 parts per character.
Extended to 7 parts, added lower case and some punctuation.
Variations exist for some non-English western languages.
* required consistency in transmission timing.
* timing varied by sender's habits.
* requires intelligent (human) processing.
* media independent, electrical, sound, light.
* fairly resistant to "noise" with correct medium choice.
# using flash light on a bright day on choppy water - bad choice.
* very low density
* fast compared to mail.
* automation can greatly improve speed.
* allowed for great transmission distances, especially if repeated.
* network/routing - possible to have branches. Don't point to point
connection between every destination.
* character not uniform fixed length units.
Not useful for storage.
Baudot (International Telegraph Alphabet #1, 1870)
Baudot -> Murray -> International Telegraph Alphabet #2
Wikipedia : Baudot code.
Image source : wikipedia Baudot code
Baudot - coding scheme and device for transmission.
5 bit binary units = 2^5 = 32 - fixed length.
Equal on/off intervals.
Encoding technique which recognized all upper case Roman/Latin characters,
numbers, punctuation, and some control 'characters'.
Friendly for automated, mechanical transmission.
First code to be generated via a standardized keyboard device.
5 key keyboard. Operator had to know correct keys for each character.
Operator had to be very consistent in the rate at which each character
was sent. ~ 30 words per minute.
2 values designated "shift signals",
allowed operator to shift to another 30 values.
One set Letter A-Z, and some controls.
2nd set Digits 0-9, bell, punctuation, other controls.
(If shift signal missed, data corrupted).
The term baud rate comes from this design.
Morse and Baudot used for data transmission not storage.
Murray - tweaked coding scheme and automated transmission. (1901)
The Murray system introduced
standard typewriter keyboard and punch to tape
Tape read mechanically constant rate.
By its nature, early form of storage.
Characters assigned to punch patterns so the most used characters
used the least number of holes to minimize wear on puncher.
(bit patterns not sequential).
It introduced CR, LF.
Used by Western Union with minor modification of code for ~ 50 years.
While useful for sending message across country, inadequate for computers.
* Insufficient character set size.
* Shifted character set inconvenient.
Hard to store shift.