memory and storage - data storage and compression

what is a bit

a binary digit that can take the value of 0 or 1

units of data

bit - 1 bit

nibble - 4 bits

byte - 8 bits

kilobyte - 1000 bytes

megabyte - 1000 kilobytes

gigabyte - 1000 megabytes

terabyte - 1000 gigabytes

petabyte - 1000 terabytes

what is data capacity

maximum amount of information that a storage device can hold

how do you convert binary to denary

write out binary headings

put in the binary digits

add up the numbers with a 1 under it

how to convert from denary to binary

write out binary headings
put a 1 in columns which the heading fits into the denary number

how do you add binary numbers

add the binary numbers, 1+1 carries the 1 to the next column

what is an overflow error

when the result of a binary addition exceeds the number of bits available

why is hexadecimal used

it’s shorter than binary meaning its easier to understand and write with fewer errors (for humans)

how to convert to hexadecimal

convert to binary (if its denary)

split the byte into 2 nibbles and convert back to denary

convert it to hexadecimal

how to convert hexadecimal to binary/denary

convert the hexadecimal digits to denary

convert the denary into binary nibbles

put the nibbles together

convert from binary to denary (if converting to denary)

what do binary shifts do

left - multiply by powers of 2

right - divide by powers of 2

disadvantage of binary shifts (2)

if bits are discarded there could be a loss of precision

overflow errors occur when the value is too big to be stored within the number of bits available

what is a character set

a defined list of characters that can be understood by a computer

what is ascii

represents basic characters needed for english using 7 bits, representing a max of 128 characters

what is extended ascii

a character set using 8 bits that can represent a max of 256 characters including maths symbols

what is unicode

a character set using 16 bits that can represent all major languages and symbols.

disadvantage of unicode

takes up more storage space

what is a bitmap image

an image made up of pixels

what is a pixel

the smallest possible element of an image

what is a vector image

an image made from maths equations and points that are infinitely scalable

what is resolution

the total amount of pixels that make up a bitmap image

how do you calculate resolution

multiply height and width of the image in pixels

what is colour depth

number of bits stored per pixel in an image

how many colours would a 4 bit image have

2⁴ = 16 colours

what happens when you increase bit depth

file size increases as number of bits per pixel increases

what happens when you increase resolution

file size increases as number of pixels increase

what is metadata

data about data

what are five examples of metadata

author, location, time, resolution, colour depth

what does frequency and amplitude in a sound wave represent

frequency - pitch

amplitude - loudness

what is A2D

when a computer converts an analogue sound wave to a digitial one

what is a sample

a measure of the amplitude of a wave

how do computers record sound waves

an anologue sound wave is sampled

amplitude is measured at set intervals

each sample is stored as a binary value

what is sample rate

the number of samples taken a second measured in hertz

what happens as you increase sample rate

the digital sound wave sounds more closer to the original and the file size increases

what happens as you increase bit depth

file size increases as the number of bits stored per sample increases

what is compression

reducing the the size of a file so that it takes up less space on secondary storage

what is lossy compression

when data is lost in order to reduce the size on secondary storage

what are three features of lossy compression

irreversible, greatly reduces file size, loses quality

what is lossless compression

when data is encoded in order to reduce the size on secondary storage

what are three features of lossless compression

reversible, reduces file size a bit, quality is not lost

what is a disadvantage of lossless compression (not about how much it can compress)

since the file has to be decompressed before being opened, it could increase file handling time