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GCSE Computer Science (Topic 3: Communication (TCP/IP 5-layer protocol…
GCSE Computer Science
Primary Memory
Random Access Memory
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Temporary storage of current programs and data,
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Cache
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Internal Memory
Data is moved to internal memory when not being actively used. Can be written to the RAM or to the registers for further processing.
If RAM is the temporary memory, You can think of the CPU as the brain of the computer. The CPU chip retrieves data from the RAM.
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Inside A Computer
Mother Board
Circuit board onto which the CPU and ROM are mounted. also provides RAM expansion, USB ports, PCI slots for additional cards and controllers
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Sound Card
Can be on the motherboard or use a PCI slot. Can be used to output sounds or record sound from an input. They convert analogue signals to digital and vice versa
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Power supply
This is responsible for maintaining a stable power source for the computer. This involves transforming AC into DC to avoid power spikes.
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Embedded systems
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Often reactive to conditions such as temperature or vibration. The system then adjusts the machine to adapt to the conditions
Combination of software and hardware to perform a specific task. The software is know as firmware which is stored on ROM or flash memory and this can be updated if necassary
Secondary Stroage
Also, know as backing storage. Data is written to secondary storage when not is not actively used. It can be retrieved at a later time. It takes longer to retrieve data from secondary storage than from memory.
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Registers
Temporary storage in the CPU. It is faster then internal memory.
Examples: Accumulator, the program counter, the memory data register and memory data address
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Von Neumann Architecture
Named after John Von Neumann in 1945. It allowed computers to be programmed more easily. Up until this time computers had a specific purpose . The architecture allowed the data and program to be stored in Ram
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Topic 3: Communication
Brief history
First networks created in 1969, known as ARPANET. This was universities connecting
their computers to share research and resources. At home and in business it was
unusual for computers to be networked until the 1990s, they were standalone
machines. The point of a network is to share files and resources and to be able to
communicate. Think about the advantages and disadvantages of a network!
Network Types
Wide Area Network (WAN)
Larger geographical areas. They could cover a city, large
organisation or several countries. The internet is an example of a WAN.
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Local Area Network (LAN)
Used across small geographical areas such as schools,
homes and small businesses
Network Typologies
Bus Network - Connected along a single cable. This is a cheap network and easy to set up. if the main cable breaks, the whole network breaks and the size of the bus networks are limited. there is also a likelihood of data collisions which slows networks
Ring Network - computers are connected in a ring. Consistent data transfer speeds. If the main cable breaks the network goes down or if one computer fails the networks is less efficient. If one section breaks the data can go around the other way.
Star Network - Connected to a central node/hub. Fats network speeds, easy to expand, better security. they are expensive to install due to the amount of cabling and additional hardware
Mesh network - similar to a star network butt every workstation is directly linked therefore no need for a hub. It is expensive to set up due to the amount of cabling required
Wired Networks
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Twisted Pair - two insulated wires twisted round each other. Most common type of cable used in networks
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Circuit switching is a method whereby a physical connection has to be established before data can be sent- like olden day telephones. Packet Switching is where each packet of data finds its own way to the destination. A packet consists of a header, the payload and the trailer.
Media Access Control (MAC) address or hardware address. This is a unique hexadecimal number given to a communication device. The address is usually stored in the devices ROM and is not meant to be changed.
IP Adress - An address allocated by a computer system on a network, usually by a Dynamic Host Configuration Protocol server (DHCP). This is a unique identifier for a computer system on a network. The IP address is often related to the MAC address to create routing tables.
Internet Domain Name System (DNS) - A database to match IP addresses to computer system resources. This allows user-friendly web addresses rather than remembering IP addresses; www.google.co.uk is far catchier than it’s IP address. When looking for a web address it is passed through DNS servers until the name is found. This continues until it reaches the top-level domains such as .com (business), .org(non-profit organisations) or .gov(governmental organisations). If the address still cannot be found a DNS server error will be returned.
TCP/IP 5-layer protocol stack - The five layers are: physical, data link, Network, Transport and application.
Network layer - Responsible for addressing and routing of data. The router determines the path based on network conditions and route packets to minimise network congestion.
Transport layer - Ensures the data is transferred from one place to another and that it is sent and received in the correct order. Acts as the interface between computers and the network.
Data link layer - Sends from the physical layer to the network layer. Divides data into data frames. Data frame consists of link layer header followed by the packet. Ensures incoming data is received correctly and an acknowledgement sent form receiver.
Application layer - Provides the interface to the software to allow it to use the network .Examples include email, FTP and the World Wide Web.
Physical Layer - Transmits raw data. Deals with creating the physical link for communicating computers. Consists of hardware such as switches and routers.
Routing
Name given to the selected paths on which packets are sent. The ‘cost’ of a route is determined by the length of the path that is taken and their speeds. Routers, switches, gateways, bridges and firewalls construct a routing table which stores the best, most efficient pathways for data to be sent. An inaccurate routing table will lead to poor network performance.
Static routing - Data travels along a present path. Easy to set up but the network can be slower if lots of data is being sent on the same path.
Dynamic routing - More complex but allows data packets to take alternative routes. More congested parts of the network can be avoided.
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Topic 10: Ethical, Legal and Environment impacts