What is data

A fact — a piece of information
- corresponds to discreete facts about phenomena from which we gain information abou the world
The concept of a value is fundamental to data
- e.g., 25, $356.00, April, "this is a sentence", colours etc
Vaues are abstract, they are interpretations of data
- There are many way of storing the same data
- e.g., 12, twelve, XII, 1100, · ··, ·----··---

How computers represent data

In Binary
Stored in one of two states, true/false, 1/0, on/off, voltage/no voltage
Each instance of a state is called a bit. (binary digit)
Values are represented as a sequence of bits.
- e.g., 1000001
- The computer doesn't "know" what any given sequence means, you know.
- could be 65, A, or anything You want it to mean

SImilar to the switch board in your home
Each switch has a number
they are all always there
you can switch the state by flipping the switch
Each switch has:
- A address/location (swtich number)
- A value (on/off)
computer languages allow us to name some of the locations, its easuer than remembering its number (variable)

The smallest unit of storage is a buit (0 or 1)
(for convenience) bit are grouped into larger units.
- a nibble is 4 bits
- a byte is 8 bits
For convenience bytes are given addresses, not nibble or bits. (they are too small to work with most of the time)

The word is the number of bits the cpu uses internally, varies between manufacturers and CPUs.
Now its usually 64 bits
amount of bits for different devices

A written symbol.
In english are represented as a single byte, (other languages use 2 bytes or more)
e.g., different types of characters
characters are joined together to make human readable numbers and words
char ch
ch is a variable name (identifier)
used to label a location in the computer's memory where a byte is stored
when the code is compile, the name is assigned an address, in memory. The meaning of that data depends on how a human interprets it. it might be small integer, or a character, or a color etc.

The computer uses ch as a integer index into a pre-existing table
the computer screen is made up of a thousand little dots called pixels. theyre in a rectangular grid like a table.a

ascii code example
There are several tables that describe what to draw
- fonts describe how to draw them
ASCII (american standard code for information) describes what should be drawn for Roman (english like) alphabets
e.g.,
- A 1000001 (65)
- B 1100001 (97)
- 9 0111001 (57)
There are only a few letter numbers and punctuation marks. The remaining ASCII code are non-printing and have other meaning (line feed, for feed, tab etcc)
ASCII characters are stored using 7-bits
- so there are 128 (2^7) possible characters
- stored as a byte with the 8th bit set to zero
- For sorting purposes characters are compared on their numeric value (called the collating sequence)
- 'A' is before 'Z' but 'a' is after 'Z'!

Other non roman languages
- greek, arabic, chinese, hebrew, japanese, thai etc.
- atrology symbols
- emoji etc
Unicode
- developed by the Unicode Consortium
- coordinated with ISO/IEC 10646
- a 21-bit code with 144,697 characters from 159 scripts
- unicode maps from character numbers (code points) into glyphs (graphical representations)
- Some(many) are reserved

How are character strings (e.g. “hello world”) stored in a computer?
Is this different between different programming languages (for example; C and Java)?