mirror of
https://github.com/jackyzha0/quartz.git
synced 2025-12-25 13:54:05 -06:00
103 lines
3.9 KiB
Markdown
103 lines
3.9 KiB
Markdown
---
|
||
title: "01-bits-and-bytes"
|
||
aliases:
|
||
tags:
|
||
- cosc204
|
||
- lecture
|
||
---
|
||
|
||
# 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
|
||
|
||
# Computer memory
|
||
- 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)
|
||
|
||
|
||
# Bits, Nibbles, Bytes
|
||
- 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 nibbles or bits. (they are too small to work with most of the time)
|
||
|
||
# A Word of memory
|
||
- 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](https://i.imgur.com/nHrz1zX.png)
|
||
|
||
# Characters
|
||
- A written symbol.
|
||
- In english are represented as a single byte, (other languages use 2 bytes or more)
|
||
- e.g., [different types of characters](https://i.imgur.com/DBLVhw8.png)
|
||
|
||
- 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.
|
||
|
||
## ASCII Character Code
|
||
|
||
|
||
1. The computer uses ch as a integer index into a pre-existing table
|
||
2. 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](https://i.imgur.com/9uvKRVo.png)
|
||
|
||
- 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'!
|
||
|
||
## Unicode
|
||
|
||
|
||
- 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
|
||
|
||
|
||
# Homework
|
||
- How are character strings (e.g. “hello world”) stored in a computer?
|
||
- Is this different between different programming languages (for example; C and Java)? |