GCSE Computer Science- Topic 1 - Details

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The physical things that make up a computer system like the CPU or motherboard.

Hardware

The programs or applications that a computer system runs like a word processor.

Software

Computers built into other devices that are usually dedicated to a single task which makes them easier to design, cheaper to produce and more efficient at doing their job.

Embedded systems

The Central Processing Unit that processes all of the data and instructions that make the system work. Depends on clock speed, cache size and number of cores.

CPU

The Control Unit is part of the CPU and its main job is to execute program instructions by following the fetch-decode-execute cycle. It also controls the flow of data inside and outside the CPU.

The Arithmetic Logic Unit does all of the calculations like simple addition, subtraction, multiplication, division as well as logic operations and binary shifts.

ALU

It is very fast memory in the CPU that stores regularly used data so the CPU can access it quickly without going to RAM. It is slower than the registers but faster than RAM. It is also very expensive and low capacity.

Cache

L1 is the quickest but has the lowest capacity. L2 is slower than L1 but has greater capacity and L3 is the slowest with the most capacity.

Cache levels

The Program Counter holds the memory address of the instruction for each cycle.

The Memory Address Register holds any memory address about to be used by the CPU.

MAR

The Memory Data Register holds the actual data or instruction which has been fetched from memory or waiting to be written to memory.

MDR

Copy memory address from PC to the MAR and copy the instruction stored in the MAR address to the MDR. Then increment the PC to the next address for the next cycle. The instruction in the MDR is then decoded by the CU and is executed.

Fetch-Decode-Execute cycle

Random Access Memory is the main memory in a computer. It can be read and written to and is volatile (requires power to keep its contents). The RAM is where all data, files and programs are stored while they are being used.

RAM

When the RAM is full, open applications that haven't been recently used are moved to a type of secondary storage called virtual memory. If the CPU needs to read data stored in virtual memory, it must move the data back to RAM which will make it slower.

Virtual Memory

Read Only Memory is non-volatile memory that can only be read and contains all the instructions a computer needs to boot up correctly called the BIOS.

ROM

The number of instructions a single processor core can carry out per second (Hz). The higher the clock speed, the greater number of instructions that can be carried out per second.

Clock Speed

Each core in a CPU can process data independently so the more cores a CPU has, the more instructions it can carry out at once.

Number of Cores

A larger CPU cache gives the CPU faster access to more data it needs to process.

Cache Size

Graphics Processing Units are specialized circuits for handling graphics and image processing. They relieve the processing load on the CPU, making it free to do other things.

GPUs

The memory areas that the CPU can access very quickly like CPU, cache, ROM and RAM. It has the fastest read/write speeds and is mostly volatile.

Primary Storage

It is where all data is stored when not in use so is non-volatile. Includes SSDs, CDs and SD cards.

Secondary storage

Hard Disk Drives are made up of a stack of magnetised metal disks where data is stored in sectors. They are popular for backing up and transporting large amounts of data. Generally very long lasting and reliable but can be damaged by shocks due to moving parts.

HDDs

A type of flash memory which is fast with no moving parts. Some examples are USB sticks and memory cards.

SSDs

Cheaper, higher capacity, longer read/write life.

Advantages of HDDs

Faster, don't need defragmenting, more shock proof, silent

Advantages of SSDs

They are very cheap, portable and won't be damaged by water or shocks but their use is declining as internet speeds have increased and modern devices don't have optical drives.

Optical Disks

Have very great capacity and are very cheap so are often used by large organisations to store huge amounts of data.

Magnetic Tapes

The Operating System provides a user interface to allow a user to interact with the computer, allows the computer to multi-task by controlling memory resources and deals with file and disk management.

Allows the user to interact with a computer system. GUIs are the most common and are designed to be easy for everyday users. Command-line interface is text based and are less resource heavy then GUIs.

User Interface

Reorganises data on a hard drive to put fragmented files back together and collects all the free space.

Defragmentation Software

Files on a hard disk are stored in available spaces and as files are moved, deleted and change size, gaps begin to appear on the disk. This makes reading and writing files slower as the head has to move back and forth across the disk.

Fragmentation

A backup is a copy of a computer system's files stored externally so it can be recovered in the event of data loss.

Backups

Where a copy is taken of every file on the system which often takes a lot of space and time but is faster to restore from.

Full Backup

When only the files created or edited since the last backup are copied which takes less storage space and are quicker.

Incremental Backup

Reduces the size of files so they take up less disk space and is used a lot on the internet to make files download quicker.

Compression Software

It scrambles the data to stop third-parties from accessing it and has to be decrypted using a special 'key'.

Encryption Software

Where the source code is made freely available so users may legally modify the code to make their own software. It is usually free and made for the greater good but there are no warranties if something goes wrong or customer support.

Open Source Software

When only the compiled code is released and is usually paid for so the modification, copying and redistribution of the code is restricted. It comes with warranties, documentation, customer support and is well tested/ reliable but can be expensive.

Proprietary Software

A Local Area Network covers a small geographical area located on a single site and all the hardware is owned by the organisation that uses it. Hardware, files and internet connection can be shared.

LAN

A Wide Area Network connects LANs in different geographical locations and organisations hire infrastructure because it is expensive. An example is the internet.

WAN

The amount of data that can be transferred in a given time and is shared between the users of a network.

Bandwidth

A Network Interface Controller is an internal piece of hardware that allows a device to connect to the internet.

NIC

They connect devices on a LAN by receiving data from one device and transmitting it to the device with the right MAC address.

Switches

They are responsible for transmitting data between networks and have a crucial role on the internet of directing data to its destination.

Routers

To set up a wireless network, you need a Wireless Access Point device which is a switch that allows devices to connect wirelessly.

WAP

It is managed by a server where files and software are usually stored. Clients send requests to the server which it processes and responds to. There are advantages such as easier back-ups, easier to install and update software, easier to keep track of files and manage network security. However, it is expensive to set up and maintain and if the server goes down the whole network does.

Client-Server network

All devices are equal and connect directly to each other so files are stored on individual devices. It is easy to maintain and there is no dependence on the server. However, there is no centralised management so devices need their updates and security installed individually. Copying files between devices can create duplicate files so it is easy to lose track.

Peer-to-Peer network

All devices are connected to a central switch or server so if one device fails the rest of the network is unaffected and it is simple to add more devices to the network. However, if it is wired every device needs a cable which can be expensive and if there is a problem with the server then the whole system goes down.

Star Topology

It is decentralised so the devices are directly or indirectly connected and data is sent across the fastest route. The main advantage is that there is no single point that it can fail however it can be expensive due to the wires needed.

Mesh Topology

A set of rules for how devices communicate and how data is transmitted across a network. They cover how communication should start and end and how data should be organised.

Protocol

Unique identifiers assigned to all network-enabled devices by the manufacturer and cannot be changed.

MAC Address

Assigned either manually or automatically before the device can access the network and are used when sending data between TCP/IP networks. Static ones are permanent and Dynamic are assigned when a device logs on to a network so change.

IP Address

Data is sent between networks in equal sized packets. These have a header which includes the packet's destination address, the source address and the packet number. Also likely to include a checksum number(form of validation).

Packets

Transmission Control Protocol sets the rules for how devices connect on the network and is responsible for splitting the data into packets and reassembling.

TCP

Internet Protocol is responsible for packet switching.

A layer is a group of protocols which have similar functions and are self-contained so the protocols in each layer do their job without affecting other layers. Each layer serves the layer above it. It breaks network communication into manageable pieces.

Layers

A network of networks- WAN.

Internet

A collection of websites that are hosted on web servers.and accessed through the HTTP protocol.

World Wide Web

Advantages: Users can access files from any connected device, easy to increase storage, no need to buy expensive hardware to store data, security, backups and updates are provided. Disadvantages: A connection to the internet is needed to access files, dependency on host for security and backups and data can be vulerable.

The Cloud

A network that is entirely software-based and can be created by partitioning off some of a physical network's bandwidth to form a separate network. Several virtual networks can exist on one physical one and each one has its own security.

Virtual Networks

When someone monitors data travelling on a network and intercepts any sensitive information they find. They are hard to detect and the best defence is data encryption.

Passive attack

When someone attacks a network with malware or other planned attacks which are more easily detected. Main defence is a firewall.

Active attack

When someone within an organisation exploits their network access to steal information.

Insider attack

A type of active attack used to gain information by cracking passwords through trial and error. They may use automated software to try hundreds of likely passwords.

Brute Force Attack

Where a hacker tries to stop users from accessing a part of a network or website by flooding it with useless traffic.

Denial-of-Service Attack

It may delete or modify files, lock files and demand a large sum of money, spyware, opening back doors and scareware.

Malware

They attach by copying themselves to certain files and users spread them by copying infected files and activate them by opening infected files.

Viruses

They self-replicated without any user help and spread very quickly.

Worms

Malware disguised as legitimate software so users install them not realising their true purpose.

Trojans

A way of gaining senstive information or illegal access to networks by influencing people like employees of large companies.

Social Engineering

When criminals send emails or texts to people claiming to be from a well known business and request the user to update their personal information, handing it all to the criminals.

Phishing

Pieces of SQL typed into a website's input box which then reveal senstive information.

SQL Injections

When organisations employ specialists to stimulate potential attacks on their network and is used to identify possible weaknesses in security.

Penetration testing

Investigations undertaken to find the cause of attacks on a network.

Network Forensics

They prevent unauthorised users accessing the network and should be strong and changed regularly.

Passwords

Control which parts of a network different groups of people can access which limit the number of insider attacks.

User Access Levels

Designed to find and stop malware from damaging a network and the devices on it. An example is firewalls.

Anti-Malware Software

When data is translated into a code which only someone with the correct key can access so unauthorised users can't access it. Encrypted text is called cipher text.

Encryption

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