Computer science unit 1
1.3
optical
solid state
magnetic
poor speed
worst capacity
cheapest per mb
highest capacity
reliable
most durable
expensive
fastest
most portable
fragile
fragile
examples: Hard dick drive
example: ssd
example: cd;rom
1.2
RANDOM ACCESS MEMORY (RAM)
READ ONLY MEMORY (ROM)
Non volatile ( keeps instructions even after being turned off)
Instructions are permanently etched into the chip
bios stored here
holds data that are currently in use
very fast
volatile
types
SRAM
DRAM
FAST
EXPENSIVE
SLOWER
CHEAPER
VIRTUAL MEMORY
when a computer runs out of ram. It will create vram on the hard drive
slow
leads to disk thrashing
1.4
1.4.1
Local area networks
Wide area networks
Has its own infrastructure
routers
switches
uses public infrastructure to lower costs
Typically found in homes/schools
connects two or more separate lans together
can create thier own connection but it is expensive
found in large businesses
Advantages of networks
share data/files/ information
share peripherals
admins
login from any computer
Network structures
client server
peer - to - peer
relies on a central server
client request services from the server (printing)
all computers on the network have equal status
each computer acts as a client and a server
files are stored on individual machines
back up must be done one an individual machine basis
files are stored centrally
suited for a low number of computers
suited for large amounts of computers
Virtual private network
Provides encrypted 'tunnel' between machines
Allows for secure transfer of data
software based private network
cables
data packets
Data is split up into pieces called packets
Each packet contains
ip address of the sender
ip address of the receiver
Its position in the sequence
Timeout time
Verification that it has arrived without corruption
packets may go by different routes and get reassembled at destination
Network hardware: specific hardware is needed to connect client to networks
Wireless access points
routers
switches
network interface card
cables
handles the packets
Used to join segments of a network togther
connects two or more devices together to stop data collision
Allows wireless devices to connect to a wired network
advantages
quick installation
no building work required
visitors can access easily
disadvantages
slower and less secure
alllows a computer to connect to a wired network
provides a unique mac address for each client
ethernet (slower)
fibre optic (fast)
factors that affect performance
Bandwidth
how fast data can be sent
measured in bits per second
The number of users
too many can slow the network
cables
wired vs wireless
fibre optic vs copper
Error rate
poor connection increases errors
Latency
A delay between sending and receiving data
The cloud
Benefits:
increase storage
access anywhere
collaborate with others
Security and privacy issues
1.5
network topologies
Mesh network
some or all devices are connected directly to each other
Most are usually connected to a node
Star network
Each devices is connected by an individual cable directly to the server
Usually used in schools and offices
1.1
central processing unit
internal components
main memory
i/o controllers
buses
the processor
external components
keyboard,mouse,printer
secondary storage
made up of billions of transistors
combined to make logic gates
very fast
fetch decodes and executes
RAM
holds data and instructions
located on motherboard
volatile
ROM
non volatile
read only
bootstrap loader held here
Used as an interface between a hardware devices external to the motherboard (keyboard mouse)
A set of wires connecting two or more components of the system
address bus
carries addresses from the processor to main memory
one directional
data bus
control bus
carries data from main memory to the processor
works both ways
data can be read/writren
controls signal are sent
instruction will be send from memory to processor
Embedded systems
computers built iinto a machine
washing machine
Von neumann architecture
Control unit
Arithmetic logic unit
performs fetch, decode and execute
contains clock for keeping time
does maths
Registers
program counter
stores the location of the next instruction
memory address register
stores the current address of data/instruction
Instruction register
Stores the instruction ready to be decoded
Accumulator
stores the result of the alu
Performance
Clock speed
measured in hertz
Bus speed (higher better)
Number of cores
Cache memory
stores fast instructions
1.7
systems software
Provides a platform users can run programs to accomplish task
Utility software
User interfaces: Features of a graphical user interface
Memory management
Programs are loaded from secondary storage to ram
The programs are put into queues and then ran in order
repeat, closed programs leave,new ones join
Device and user and file management
Device driver
This translates commands from the operating systems into hardware specific commands the peripheral understands
User management
Provides different users to login
file management
How folders and files are presented in a computer
files dont exist
As files are saved and deleted the hard disk will become fragmented
1.8
Ethical concerns
Pirating
For
against
people cant afford it
doesnt hurt anyone
the creators should protect it
Everyone is doing it
Its stealing
It costs them to make it
Its illegal
Should the Internet be regulated
For
against
Children use it
It has illegal content
Freedom of speech
Its too large
Parents should take responsibility
Privacy (recording)
for
against
Could save lives
If you have nothing to hide its fine
help disabled people
May be using our data
We are entitled to our privacy
Legal issues
Data protection act
Data should be relevant
Must be secured
Must be only used for the purpose specified
Users have the right to access the data
Computer misuse act
You cant access any unathorised data
You cant access with the intent to commit further offences
You cant access with the intent to modify data (viruses)
Copyright design and parent act
You cant copy,modify or distribute copyrighted material without permission
Creative commons licensing
A way to grant copyright permission to creative work
Freedom of information act
Provides the public with access to information held by public authorities
Members of public can request
They must publish this data
Cultural issues
Some countries have increased privacy
Some countries read right to left
Violations of hate speech
Environmental issues
Produces alot of fossil fuel to produce a computer
The resources to make computers are finite
Data centres account for 2% of energy usage
Computers add to the land fill
1.6
Malware
Phishing
Sending emails pretending to be someone else
Social engineering
Protection
Staff training
Brute force attack
A trail and error method of attempting passwords
Protection
better passwords
2 factor authentication
Progressive delays
Denial of service
Flooding a server with traffic so it cant process requests
Protection
Strong firewall
Packet filters on routers
Well configured web server
Data interception
Interception of data using a packet sniffer
Physical interception because user has left computer on or password written down
Protection
Encryption
Virtual private networks
Train staff
SQL Injection
A technique used to view or change data in a database by inserting code
Protection
Good validation on input boxes
Using parameter queries
Penetration testing
Ethernet (wired connections)
Stable connection
Reduced possibility of hacking
More secure
Faster transfer speed
Good quality of signal
expensive cost of wire
Wifi (wireless)
Cheap set up
User have more freedom
lower transfer speeds
More vulnerable to hacking
Interference can occur
Encryption
Scrambles the data so it cant be read
A key is needed to decode it
Protocol
Media access control (mac)
A unique address for the device
Its embedded in the hardware and cant be changed
Its made up of 48 bits (6 bytes) written as hex
IP Addresses
Each device on the network has a unique IP address
The address is written in denary
The first number indicates the class of network the user is on
Application protocols (allows the two+ computers communicate)
Hyper text transfer protocol
Hyper text transfer protocol secure
File transfer protocol
Post office protocol
Internet message access protocol
Simple mail transfer protocol
Network layers
Level 7: Application layer
Contains all the application that may with to exchange data of files
Level 6: Presentation layer
Layer 4: Transport layer
Creating and sequencing packets on a WAN
Divides the data into packets and sends them to the internet layer
Layer 3: Network layer
Layer 2: Data link layer
Layer 1: Physical layer
Routing the packets on a wan
Creating and routing frames on a lan. Error checking
Methods of encoding bits onto wired and wireless frequencies and channels
Clock
Uses address bus to acess memory
Encryption
Defragmentation
Reorganises files to put the fragments back together
Scrambles data that has to be decrypted to be readable, usually a key is used
Data compression
Software that reduces the size of a file to lower disk space
Back up software
Takes up a copy of files to prevent data loss