1. Data storage Flashcards
What are Bits?
Binary digit that has two values.
What does a bit patterns represent?
Numbers, text, images, sound and truth values
Boolean operation?
Are operations on truth values
Boolean operators:
And
Or
XOR
Not
What is a gate?
A gate is a device that computes a Boolean operation.
What does those Boolean numbers represent?
AND: x= 1, y= 0
AND: x=1, y= 1
OR : x= 0, y= 1
OR: x= 1, y= 1
XOR: x= 1,y= 1
NOT x: x= 0
0
1
1
1
0
1
What is a Hexadecimal notation?
Is used as a base and has four bit pattern that represents one number between 0 and 9 and six different letters.
What are the letters in a Hexadecimal notation and what they represent?
A-10 , B-11, C-12, D-13, E-14, F-15
What does this bit patterns represent?
0000/ 0
0001/ 1
0010/ 2
0011/ 3
0100/ 4
0101/ 5
0110/ 6
0111/ 7
1000/ 8
1100/ 9
1010/A
1011/B
1100/C
1101/D
1110/E
1111/F
Main memory (RAM) premiär minne.
Consist of large number of circuits each capable of storing a single bit.
How are main memory organized?
It is organized in units called memory cells, with a typical size of 8bits
What are bytes?
Bytes are a group of 8 bits
What do you assign memory cells?
Memory cells are assigned numbers (starting with 0) which are called addresses
What are addresses for?
The addresses works as a map, when we need information we can access it quickly by going to the address of a cell where the cell itself is implicit. They are stored (implicit) in order so we can access it quickly
Types of Mass storage?
-The magnetic disks such as HDD’s
-Optical discs: CD’s DVD’s and blue rays
- Flash memory, solid state drive: SSD and secure digital: SD
what are the advantages of mass storage over main memory?
- less volatile, they are not dependent on currents.
- lower costs
- larger storage capacities.
how do you represent text?
character encodings - mapping bit patterns to characters. mellan en bit mönster och ett tecken.
what is the first Standard code?
ASCII is the first (American Standard Code for Information Interchange) 7-bits: 128 characters.
How are ASCII characters represented?
they are represented in zeros and ones which are assigned to characters. the first bunch are only commands and when we come to 0100000 it starts with characters that we can print out. (show on the screen)
why is there numbers as characters?
In ASCII, zero (0) for example is a character and not a number so it doesn’t have a numerical value. its represented as 0110000.
the problem with ASCII?
ASCII doesn’t have the characters that are not in the English language, so there is a non standardized ASCII which has 8-bits that can represent 256 characters instead of 7-bits
there is problems with using the different standards:
- First it becomes a not standard, as in there are too many.
- Second the machines built with one standard cant be read correctly by another machine with a different standard
How did we solve it?
To solve the standard problem we introduced Unicode.
- Unicode is able to represent all characters in all languages.
- The first 128 is the same as ASCII.
- UTF-8 is (Unicode transformation Format 8-bit) it uses 8 or more bits per character.
- the ASCII characters can then be represented with 8-bits but for example öåä needs 16-bits to be represented in UTF-8.
- there can be 24-bits and 32-bits and so on.
- Although not everyone uses it and we can see it till today that sometimes other people cant read or receive the special characters.
How do we represent images?
we do it in two steps:
- the first is to use a grid-pattern over the image and each square represent a pixel (picture element) the resolution is how many pixels we have.
