Memory and Storage Flashcards
Bits
. All data in a computer system is made up of bits.
A single bit is a 0 or a 1.
. 4 bits is called a nibble
. 8 bits is called a byte - a byte can store a single character
Units scale
. 8 bits is called a byte
. 1000 bytes is called a kilobyte
. 1000 megabytes is called a gigabyte
. 1000 gigabytes is called a petabyte
. 1000 terabytes is called a petabyte
What is binary
Binary is a base 2 number system. This means that it only has 2 possible values - 0 or 1.
What is denary
Denary (also known as decimal) is the number system that you’ve been using since primary school.
Denary is a base 10 number system. This means that it has 10 possible values - 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9.
What is hexadecimal
Hexadecimal is a base 16 number system. This means that it has 16 possible values - 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E and F.
Hexadecimal is used as a shorthand for binary because it uses fewer characters to write the same value.
This makes hexadecimal less prone to errors when reading or writing it, compared to binary. For example, 1001 1110 1011 in binary is 9EB in hexadecimal.
Hexadecimal only uses single-character values. Double-digit numbers are converted into letters -
What is an overflow error
An overflow error occurs when a binary value is too large to be stored in the bits available.
with a byte (8 bits) the largest number that can be held is 255. Therefore any sum of two binary numbers that is greater than 255 will result in an overflow error as it is too large to be held in 8 bits.
What is a character set
A character set is a table that matches together a character and a binary value.
Each character in a character set has a unique binary number matched with it.
Character sets are necessary as they allow computers to exchange data and humans to input characters.
ASCII
ASCII (American Standard Code for Information Interchange) is a common character set which does not take up much memory space.
It is important to understand that the number of characters that can be stored is limited by the bits available - ASCII uses 1 byte (8 bits) which only gives 256 possible characters.
This is enough for the English language but it can’t be used for other languages or all punctuation symbols 01101010 = 256 possible characters
8 bits (1 byte)
Unicode
Unicode is a more popular character set because it uses 2 bytes
(16 bits) that allow for 65,536 possible characters.
The extra byte allows many different languages to be
represented, as well as thousands of symbols and emojis.
However Unicode requires more memory to store each
character than ASCII as it uses an extra byte.
1000101101001111 = 65,536 possible characters
16 bits (2 bytes)
Character sets
Character sets are logically ordered.
For example, the binary code for A is 01000001, B is 01000010 and C is 01000011 as the code increases by 1 with each character.
File Size of Text Files
The file size of a text file is calculated as shown below:
bits per character × number of characters
Example:
A small text file uses the ASCII character set (which uses 8 bits per character).
There are 300 characters in the file.
300 x 8 = 2,400 bits
This could be simplified as 300 bytes or 0.3 kilobytes.
Bitmap images
Bitmap images are made of pixels - single-colour squares - arranged on a grid.
Each pixel is assigned a binary value which represents the colour of that pixel.
The quality of a bitmap image depends on the total amount of pixels, this is known at the image resolution.
Because it is made of pixels, scaling a bitmap image up will result in a visible loss of quality.
Most images on computers are bitmaps, such as photos and screenshots.
Vector images
Vector images are drawn by the computer following precise mathematical instructions to create lines and objects.
Vectors are usually smaller in file size compared to bitmaps because each pixel in a bitmap is stored as an individual binary value.
Vectors can be scaled up without any loss of quality and are typically used for logos and animations.
How to calculate file size of a bitmap
The resolution of an image is the width in
pixels multiplied by the height in pixels.
The colour depth (also known as bit depth) is the number of bits that are used to represent each pixel’s colour.
1 bit represents 2 colours (0 or 1 / black or white). 2 bits will allow for 4 colours, 3 bits for 8 colours, 4 for 16 etc.
A colour
depth of 1 byte (8 bits) allows for 256 different colours. Remember you must multiply the colour depth, not the number of available colours (e.g. 8 not 256).
The RGB (Red, Green, Blue) colour model uses 3 bytes (a byte of 256 red shades, a byte of 256 green shades and a byte of 256 blue shades) that together can represent 16.7 million different colours.
Metadata
Metadata is additional data about a file. Common image metadata includes:
* Height in pixels,
Width in pixels,
Colour depth,
Resolution,
Geolocation,
* Date created,
* Last edited,
File type,
* Author details
Metadata is important, For example, the dimensions must be known so the image can be displayed correctly.
