COMPUTING

Von Neumann Architecture

made up of CPU and memory which are interconnected and store instructions and data

components of CPU and their purposes

registers - location in CPU that stores addresses and data which can be accessed quickly

cache - stores frequently used instructions

control unit - decodes instructions and sends signals to other components on how to respond to this instruction

ALU - performs arithmetic calculations and logical decisions

clock - controls rate at which cycles are processed every second

purpose of CPU

fetch decode and execute instruction

types of registers and purpose

• Program Counter - stores next instruction ready to be used

• MAR - stores location of next address to be fetched

• MDR - data written to and from main memory

• Accumulator - stores results of arithmetic calculations

Performance of CPU (factors)

• Cache size - increased = more instructions can be stored in CPU so they don’t need to be fetched from main memory = efficient

• Clock speed - more tasks executed per second so program responds faster

• number of cores (execute instructions) - more = instruction split between processors so they can be executed simultaneously so faster

embedded systems

computer systems found in other devices, designed to perform a set of specific functions

real time systems

well defined systems with fixed time constraints, provide and immediate response to an input

Primary Storage

holds memory for a short period of time whilst the computer is running

RAM and ROM

RAM vs ROM

RAM - volatile, read and write, constantly changing contents, program/data currently in use.

ROM - non-volatile, read only, permanent (rarely change)

Secondary storage

ability to hold files even if computer switched off

• magnetic

• solid state

• optical

Magnetic storage

Magnetises data e.g. hard drive

+ expensive but holds value

+ high capacity

- not very durable

- eventually becomes deteriorated (low reliability)

- not portable

- not very fast

Solid State

Uses flash memory e.g SD card

+high capacity

+ durable

+ high speed

+ portable

- expensive

- low reliability

Optical

Uses lasers e.g. CD

+ cheap

+ portable

- not very durable

- low capacity

- low reliability

- slow

sound file size

sample rate x bit depth x duration

image file size

colour depth x image width x image depth

text file size

bits per character x number of characters

Units of data storage

bit - 0/1

nibble - 4 bits

byte - 8 bits

KB - 1K bytes

MB - 1K KB

GB - 1K MB

TB - 1K GB

PB - 1K TB

binary to denary number order and left, right shifts

128 64 32 16 8 4 2 1

shift left is x2

255 bits per byte

Hexadecimals

Base 16

1 - 9 is standard

10 - A

11 - B

12 - C

13 - D

14 - E

15 - F

Character Sets

defined list of characters

ASCII :

• 0-127

• 7 bits

• numbers, letters, symbols

EXTENDED ASCII:

• 0-255

• 8 bits

• included foreign languages and special symbols asw

UNICODE :

• 143859 characters

• universal set, most languages

bitmap image

a digital image made up of pixels

colour depth

number of possible colours that could be represented in each pixel

resolution

how many pixels are displayed per inch of image

sampling

sound is recorded at regular intervals

bit depth

number of bits available for each sample

compression

reducing size of a file

LOSSY:

• reconstructs data and some data lost

• irreversible

• impacts quality

• file size significantly reduced

• e.g. JPG

LOSSLESS:

• data reconstructed but none removed

• reversible

• quality retained

• file still relatively large

• e.g. PNG

Network

group of interconnected devices with intention of sharing resources over a network

LAN

local area network, covers a small geographical area

e.g home

WAN

wide area network, covers a large geographical area, made up of series of LANs

e.g internet

Client Server Network

all files can be stored centrally, so can be accessed from any computer.

server has sole responsibility

e.g school

Peer to peer network

files stored on own computers, each person needs their own backups, softwares etc

all devices have equal responsibility

e.g home

network hardware

devices required for communication and interaction over a computer network

transmission media

technology used to transmit data from sender to receiver usually in form of cable

Network hardware exmples

• Network Interface Controller (NIC) - connect computer to network

• Router - connects different networks together

• Hub - connects devices together on a network

Transmission media examples

• Switch - connects devices and forwards data using mac addresses

• Wireless access points - allows wireless devices to connect on a network

• server - provides services / data to other devices a network..