Studied by 9 people
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
Note 
Flashcard (78)