CS paper 2

3.3,3.4

algorithm

a sequence of steps that can be followed to complete a task

computer program

an implementation of an algorithm

binary

base 2

denary

base 10

hexadecimal

base 16

why do computers use binary?

easy to represent,

bit

a single binary digit

nibble

4 bits

byte

8 bits

why do we use hexadecimal in computing?

it is easier for humans to read than binary

left binary shift

multiplies a number

right binary shift

divides a number

what do binary shifts do?

multiplies/divides a number by 2

how many bits are used to encode in ASCII?

7 bits

how many bits are used to encode in unicode?

16 bits

advantages of ASCII

takes up less space

advantages of unicode

can encode more characters eg in other languages

how many codes are the same in ASCII and unicode

the first 127

pixel

picture element

bitmap image

made up of pixels

vector graphics

shapes are used to represent an image

colour depth

number of bits used to represent each pixel

image file size calculation in bytes

height x width x colour depth /8

what are vector graphics better for?

artificial images

what are bitmap images better for?

representing more complex images or natural landscapes

amplitude

the maximum displacement of a wave

frequency

the number of cycles per second

sample

measure of amplitude at a given point in time

sample rate

number of samples taken per second

sample resolution

the number of bits used to represent each sample

sound file size calculation in bytes

length x sample rate x sample resolution

how are sound waves converted from analogue to digital sound?

the signal is sampled at regular intervals, the samples are approximated, each integer is encoded as a binary number with a fixed number of bits

huffman coding

a lossless compression method based on how frequently a piece of data occurs

lossless compression

no data is lost and the file can be decompressed with all of tis information intact

data compression

storing a file using less memory

lossy compression

some data is lost when the file is compressed

huffman compressed file size

total bits x frequency of each character x 7 bit ASCII

run length encoding (RLE)

reduces the physical size of repeating strings into two bytes

what are the two bytes in RLE

byte 1 : represent the number of characters in a run byte 2 : the value of the character in the run

advantage of RLE

good when there are long runs of repeating characters

analogue

data which can use any value in a continuous range

software

computer programs that give instructions to the computer to run

application software

a program designed to perform a specific task that the user interacts with directly

system software

controls the computer hardware and manages the application software

network

two or more computers that are connected together

the internet

a global network of interconnected computers, refers to the hardware

world wide web

a service that has web pages and other data

LAN

local area network

WAN

wide area network

PAN

personal area network

advantages of a network

can share resources, allows communication, allows easier network

disadvantages of a network

greater security risk, malware can spread more easily, if there is a problem it can affect the whole network

personal area network

set up around an individual person

example of a PAN

bluetooth

local area network

covers a relatively small geographical area

wide area network

covers a much wider geographical area, made up of many local area networks

WLAN

wireless local area network

wireless access point (WAP)

a switch that allows devices to connect wirelessly

Boolean logic

a data type with two values, true or false

what makes up logic gates

transistors

logic gates

form the basis of decision making in a computer

NOT gate

outputs the opposite of the input

AND gate

only true if both inputs are true

OR gate

true if either of the inputs are true

XOR gate

only true if one of the inputs is true not both

von Neumann architecture

the design of a CPU created by von Neumann in 1945

stored program concept

where program instructions and the data to be processed are stored in the same memory system

Arithmetic logic unit (ALU)

where arithmetic and logic operations take place

Control unit (CU)

controls and monitors data transfer between different input and output hardware and decodes machine code

Clock

keeps the CPU components synchronised

Central Processing unit (CPU)

controls the interpretation and executuon of instructions in a computer

bus

wires through which data is transferred

registers

memory locations in the CPU used to store frequently accessed data and instructions

data bus

carries data between components

address bus

carries the memory address to find the next instruction

control bus

carries instructions from the CPU

instruction set

a set of commands for the CPU that tells it how to perform arithmetic and logic operations, handle data and read/write to memory, and control the flow of code

fetch execute cycle

fetch, decode, execute

RAM

random access memory

is main memory volatile

yes

volatile memory

the content is erased when the computer is turned off

ROM

read only memory

is secondary storage volatile

no

BIOS

basic input output system

what does BIOS do

tells the CPU to perform self checks and set up the computer by testing the memory, checking what hardware is present and coping the operating system into the RAM

main memory

where all data, files and programs are stored while they are being used

which memory type can be read and written to

RAM

secondary storage

used to save files and holds software like the operating system

Magnetic hard disk drive (HDD)

tracks with tiny magnets, the polarity of the magnets determines the binary digit, concentric rings of magnets

advantage of HDD

cheap

disadvantages of HDD

moving parts can break, electromagnetic surge could corrupt data, slow speed of read/write access

optical disk (CD)

track with pits and land, uses a laser to read data

advantage of optical disk

can transfer easily between computers

disadvantages of optical disk

can scratch easily, not much storage, no unlimited writes

solid state drive (SSD)

uses transistors with electrons

advantages of SSD

much faster, reliable when reading, quiet

disadvantages of SSD

more expensive, less reliable when writing

operating system

most important piece of system software

what does the operating system do

manages the processor, memory, input/output devices, applications and security

disk defragmentation

organises files on a disk to be located contiguously