Computer Science

paper 1

1.2

1.2.1 memory

volatile

ROM is non-volatile memory which stores things like the BIOS

Virtual memory is used as RAM when The RAM is full virtual memory is located on the hard disc drive

1.2.2 storage

magnetic storage stores data in domains some of its advantages is that it has a huge capacity and the cheapest per GB but it has moving parts and a magnetic field will erase all data

Optical storage stores data in pits which are cut by a laser optical storage is portable and it has a low cost for storing small amounts but it is not very robust and slow to access and write data on to it and its cost is high for large amounts of data

solid state storage holds data using electronic switches it is very portable robust and data can be access very fast but its very expensive and you can only change the data on it for a limited amount of times

1.2.3 units of storage

a bit is a single binary 1 or 0

a nibble is 4 bits

a byte is 8 bits

a kilobyte is 1024 bytes

a megabyte is 1024 kilobytes

a gigabyte is 1024 megabytes

a terabyte is 1024 gigabytes

a petabyte is 1024 terabytes

1.2.4 data storage

characters

images

numbers

sound

character sets are a set of binary values which makes up letters symbols and words there are 3 types

Extended ASCII-256 possible characters

Unicode-65,000+ characters

ASCII-127 possible characters

Binary is the language of a computer on how it understands what to do. binary is only made up of 1's and 0's and binary is a base2 system because it goes up 2times every time

image

Paper 2

loses everything when the power is turnt off

RAM is volatile memory that deals with programs that are currently in use

click to edit

Color depth is the amount of colors used in an image

a pixel is a picture element which is very small and lots together make up pictures

resolution is the amount of pixels in an image 32 x 32 just means 32 pixels wide and 32 pixels high

analogue sound is the sound that humans hear

anolgue sound is turned digital using an Analogue to digital converter (AD)

a sample is a recording at certain time intervals

the sample rate is how many samples are taken per second

bit depth is the number of bits used to record each sample

image

1.2.5 Compression

lossy compression

lossless compression

this is when you sacrifice some of the quality of the image to save storage space

this is when you delete all of the unnecessary parts of the image to save space but the quality stays the same

image before compression

image before compression

image after compression

image after compression

1.3

Computer networks, connections and protocols

1.3.1 Networks and topologies

A computer network is 2 or more devices connected together

computer networks are useful because you can easily share documents software and devices

LAN is a collection of devices connected together in a small space.

WAN is 2 or more LAN's connected together over a large geographical area. for example a LAN in London and a LAN in New York connected together is a WAN.