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Learn about the three logical operators - NOT, AND and OR - as well as truth tables. Based on the J277 OCR GCSE Computer Science specification (first taught from 2020 onwards). 4.1: Boolean Logic Exam Board: OCR Specification: J277 Watch on YouTube : Boolean Operators & Truth Tables Logic Gate Diagrams What is a logical operator? Inside of each computer system are millions of transistors . These are tiny switches that can either be turned on (represented in binary by the number 1 ) or turned off (represented by 0 ). Logical operators are symbols used to represent circuits of transistors within a computer. The three most common operators are: NOT AND OR What is a truth table? Truth tables are used to show all possible inputs and the associated output for each input . The input and output values in a truth table must be a Boolean value - usually 0 or 1 but occasionally True or False. NOT AND OR A NOT logical operator will produce an output which is the opposite of the input . NOT is also known as Negation . The symbol for NOT is ¬ An AND logical operator will output 1 only if both inputs are also 1 . AND is also known as Conjunction . The symbol for AND is ∧ An OR logical operator will output 1 if either input is 1 . OR is also known as Disjunction . The symbol for OR is ∨ NOT Logic Gate AND Logic Gate Symbol OR Logic Gate Symbol Truth Table Truth Table Truth Table Multiple Operators Exam questions could ask you complete truth tables that use more than one logical operator . Work out each column in turn from left to right and look carefully at which preceding column you need to use. NOT B A AND NOT B A OR (A AND NOT B) As binary is a base-2 number system , the number of rows required in a truth table will double with each new input in the expression in order to show the unique combinations of inputs. The examples above use just two inputs (A + B) so 4 rows are required. e.g. A = 2 rows / A + B = 4 rows / A, B + C = 8 rows / A, B, C + D = 16 rows Logic Diagrams You may be asked in an exam to d raw a logic diagram when given a logical expression . Draw any NOT symbols or expressions in brackets first. A logic diagram for C = ¬A ∧ B A logic diagram for D = C ∨ (A ∧ B) Q uesto's Q uestions 4.1 - Boolean Logic: 1. Copy and complete the following truth tables: 1b. Simplify the expression in the second truth table. 2a. A cinema uses a computer system to monitor how many seats have been allocated for upcoming movies. If both the premium seats and the standard seats are sold out then the system will display a message. State the type of logical operator in this example. 2b. For the more popular movies, the cinema's computer system will also display a message if either the premium seats or the standard seats have exclusively been sold out. However, it will not output a message when both have been sold out. State the type of logical operator in this example. 3. Draw a logic diagram for C = (¬B v A) ∧ A . 3.2 - Testing Theory Topics 5.1 - Languages & Translators

Learn about the role of different server types including file, application, print, email, mail servers and the hypervisor. Based on the 2016 OCR Cambridge Technicals Level 3 IT specification. 3.1 - Server Types Exam Board: OCR Specification: 2016 - Unit 1 What is a server? A server is a powerful dedicated system on a network . It requires increased memory , storage and processing power than traditional computer systems to fulfill its role across the network. Servers need to be scalable - this means they must be adaptable and able to efficiently manage the needs of connected systems if more are added or some are removed . Servers have different roles so a company may use multiple , separate server types within their organisation, each with a specific purpose . Having separate servers is costly but beneficial as if one loses connection , others may still be usable . Also a server will be more efficient if it is only managing one resource (e.g. printers) at a time . File Server A file server centrally stores and manages files so that other systems on the network can access them. The server provides access security , ensuring that only users of the appropriate access level can access files. File servers can be used to automatically backup files , as per the organisation's disaster recovery policy. Using a file server frees up physical storage space within a business and can provide printing services too. Printer Server These servers control any printers on a network and manage printing requests by sending the document to an appropriate printer. Print servers use spooling to queue print jobs so that they are printed when the printer is ready. If a fault occurs with a certain printer, work can be automatically diverted to another available printer. Application Server These servers allow users to access shared applications on a network. All users will be able to access common applications like email software or word processing, but the server will also restrict certain applications to those with invalid access levels (such as hiding financial databases from employees outside of the finance department). Application updates can be simply deployed to the application server only , avoiding individual updates for each system and saving a lot of time . Installers can be hosted on an application server, allowing the software to be easily installed on other connected machines . Database Server These servers manage database software that users on the network can access and use to manipulate data . Data held on the server will be stored in a database accessible from multiple connected computers . The data can be modified using query languages such as SQL. Storing data on a database server, rather than individual computers, is more reliable . A database server for a business also allows for scaling - for example, the database can be increased in size if the customer base grows. Web Server A web server manages HTTP requests from connected devices to display web pages on web browsers . A request (e.g. csnewbs.com) is sent to the web server. The server contains a list of known URLs and their matching IP addresses . The server contacts the server where the web page is held and delivers the web page to the client . Mail Server These servers send and receive emails using email protocols (SMTP & POP) allowing email communication between other mail servers on other networks. The server makes sure emails are delivered to the correct user on the network. Email servers can store company address books making internal communication easier for organisations. The server may have anti-spam functions to reduce junk mail. Hypervisor A hypervisor allows a host machine to operate virtual machines as guest systems. The virtual machines share the resources of the host , including its memory, processing power and storage space. This type of technology is called virtualisation . The guest machines are isolated so if one failed, the other guests and the hosts are not affected - demonstrating good security . The hypervisor optimises the hardware of the host server to allow the virtual machines to run as efficiently as possible. Q uesto's Q uestions 3.1 - Server Types: 1a. What is a server ? Why does it need to be scalable ? [2 ] 1b. Give two reasons why a company may use multiple , separate servers . [2 ] 1c. State the 7 types of server . [1 each ] 2. A medium-sized animation company working on a movie are considering buying a server. Describe each type of server and the different roles they have. a. File Server b. Printer Server c. Application Server d. Database Server e. Web Server f. Mail Server g. Hypervisor [4 each ] 3. What type of technology does a hypervisor use to control multiple virtual machines? [1 ] 2.7 - Protocols Topic List 3.2 - Virtualisation

Learn about the differences between wired and wireless networks. Based on the J277 OCR GCSE Computer Science specification (first taught from 2020 onwards). 3.2a: Wired & Wireless Networks Exam Board: OCR Specification: J277 Watch on YouTube : Wired Networks Wireless Networks Encryption Wired Connections Wireless Connections Wireless connections, such as WiFi or Bluetooth , use no cables but require a wireless network interface card (WNIC ). Wireless connections generally have a slower speed and can be affected by the computer's distance from the wireless router as well as obstacles like walls or bad weather. Wired connections use physical cables , such as copper or fibre optic wires , and require a network interface card (NIC ) to connect to a network. These wired connections use a wired connection protocol - most commonly Ethernet . Restricted Movement Faster More Secure NIC Required Freedom of Movement Slower Less Secure WNIC Required Encryption Wireless connections are less secure and require encryption . Encryption is the process of scrambling data into an unreadable format so that attackers cannot understand it if intercepted during transmission. The original data (known as plaintext ) is converted to scrambled ciphertext using an encryption key . Only at the correct destination will the encryption key be used to convert the ciphertext back into plaintext to be understood by the receiving computer. Q uesto's Q uestions 3.2a - Wired & Wireless Networks: 1. Briefly compare wired and wireless networks in terms of movement , transmission speed , security and required hardware . You could answer this in the form of a table. [ 8 ] 3.1b - Network Hardware & Internet Theory Topics 3.2b - Protocols & Layers

Learn about the different types of organisations that hold information. Also, consider the differences between urban and rural connections and remote locations. Based on the 2016 OCR Cambridge Technicals Level 3 IT specification for Unit 2. 1.1 - Holders of Information Exam Board: OCR Specification: 2016 - Unit 2 Categories of Information Holders Organisations that store and process information can be put into seven different categories : Business A business will hold information on all of its employees , including their date of birth, address and financial information , allowing them to be paid at the end of each month. Businesses will also hold commercial information about their organisation such as profits and losses, product descriptions and historical data . Many companies may record information about their competitors and general marketing data. Government The government will hold a huge amount of information about all citizens in the country including financial earnings, tax paid, births and deaths . The electoral roll holds information about addresses . A national census is taken every 10 years in the UK (the next census is in 2021) that records extensive data about everyone living in the country. The government also stores information about other countries and shares some of this publicly, such as the Foreign Office posting travel advice . Individual Education Educational organisations , such as schools, colleges and universities will hold information about current and past students as well as staff. Student information such as addresses, attendance records and examination history will be recorded, as well as contact information for parents and guardians. Teacher information will be stored too, as well as students that previously attended the institution, even for a number of years after they have left. An individual will hold information about themselves , either in their head or on paper or electronically. This includes their name, date of birth, address, usernames and passwords . Individuals will store information of others , such as phone numbers, social media details and email addresses . Other information will be about organisations , such as the address of their favourite restaurant, opening hours of the local cinema or the telephone number from a catchy advert. Healthcare Healthcare services , like the NHS in the United Kingdom, will hold entire medical histories for each civilian in the country. This includes basic personal information such as current address and date of birth but much more detailed data too like previous illnesses and operations, blood type, allergies and prescriptions . The data stored by healthcare organisations is usually confidential and should not be shared by anyone other than the citizen in question. Charity & Community Charities may hold financial information of donors who give money to them, as well as information about the different projects that the donations are funding. Charities such as the British Heart Foundation might have physical addresses on the high street so information may be kept about the shops too. Community organisations like sport centres or religious institutions may hold information on members and matches, meetings or events . Comparison of Locations The location of systems and data affects access speed and network quality . The digital divide is the gap between people who do and do not have easy access to computers and networks . Developed vs. Developing Countries Developed countries , like areas of Western Europe, North America and East Asia, have a more developed technology and industry base with more funding available for information infrastructures such as cabling and high-speed access . Developing countries , like areas of Africa and Central Asia, have unstable governments and slower access (if any) to the internet . Less money is spent on technology and improving broadband speed and expensive equipment like computers cannot be purchased on low wages . Urban vs. Rural Urban locations like towns and cities have a high population density . Because there are so many people, councils and IT companies will spend a lot of money on internet infrastructure such as cabling and installing high-speed lines . In Rural locations like the countryside, the population is sparse and settlements may be far apart so internet access is poorer and broadband speeds are slower . This means accessing information on the internet is more difficult . Internet Access from Remote Locations Remote locations (such as the countryside or difficult-to-reach areas like mountains or deserts) might have limited internet access . Fast fixed broadband is expensive to install and many providers simply won't invest in rural areas as it is not economically viable . Some areas, usually those with a very small or temporary population, might have no fixed internet access which will make it difficult for an individual or organisation to communicate or work online. Many remote locations have some form of internet but download speeds will be slow or interrupted due to intermittent connection . This makes it difficult to work online and could take a long time to access webpages or document stores. Alternatives to fixed broadband in remote locations include mobile broadband and satellite broadband . Mobile broadband is generally not designed for home use and would be very expensive for everyday use , plus the remote location will generally mean mobile coverage could also be weak . Satellite broadband requires a dish with an unrestricted view of the sky. Satellite broadband has a relatively high internet speed but will cost a lot to install and has a high latency (more chance of experiencing lag). Q uesto's Q uestions 1.1 - Holders of Information: 1a. State the 7 categories of information holders . [7 ] 1b. For each of the 7 categories , briefly describe 3 different pieces of information that may be stored by the information holder. For example, a charity may store the financial information of donors. [3 each ] 2. What is the digital divide ? [2 ] 3. Describe the differences in information access for the following locations : a. Developed vs. developing countries b. Urban vs. rural areas c. Remote locations [4 each ] Topic List 1.2 - Storage Media

A glossary of important code to be used in Greenfoot, such as random movement, using a counter removing objects and sound. Aimed at the Eduqas / WJEC GCSE specification. Greenfoot Code Glossary Greenfoot Home This code will work for Version 2.4.2 which is used in Component 2 of the 2016 WJEC/Edquas specification . Key Down 270 if (Greenfoot.isKeyDown("right" )) { setRotation(0); move(1); } 180 90 0 Bounce At Edge if (isAtEdge()) { turn(180); } move(1); if (Greenfoot.getRandomNumber(10)<1) { turn(Greenfoot.getRandomNumber(90) - 45); } Random Remove Object if (isTouching(Apple.class )) { removeTouching(Apple.class ); } Play Sound Greenfoot.playSound("pop.wav" ); Stop Greenfoot.stop(); Counter - (Write this code when an object is removed) Counter counter = (Counter) getWorld().getObjects(Counter.class ).get(0); counter.add(1); Stuck? If you start typing but can't remember what commands come next, press Ctrl and Space together to show a list of all possible commands that you can use.

The fourth part of a quick guide to the basics of Python aimed at Key Stage 3 students. Learn about calculations and simple mathematical operators. Python - #4 - Calculations 1. Creating Calculations To add in Python use + To subtract in Python use - To multiply in Python use * To divide in Python use / Task 1 - Create a new Python program and save the file as 4-Calculations.py Print 4 different calculations - use each operator once.(add/subtract/multiply/divide) Python is very clever, so don't be afraid to make your own calculations using larger numbers and more than one operator . 2. Using Inputs and Calculations You can ask the user to enter numbers by writing input lines. Python can then perform calculations using the numbers that the user has entered. Don't forget to add int ( and double close brackets when using numbers ! Task 2 - Copy the new code from the picture. Change the text and num1 so you are dividing by 5 not 3. Don't delete your earlier code , just add this underneath. I have cropped the images to make the new code clearer. 3. Using Calculations in a Sentence When we have printed the calculations so far, they have not been very informative! You can print calculations together with sentences so that they mean more. Use a comma ( , ) between calculations and sentences . Task 3 - Use the pictures to help you add commas and sentences to your program to be more informative. Challenge Programs Use everything that you have learned on this page to help you create these programs... Challenge Task 1 - Multiplication Create a new Python program. Save it as ' 4 -Multiplication.py ' Add a comment at the top with your name and the date. Write an input line ( don't forget int ! ) that asks the user to enter number 1. Write an input line ( don't forget int ! ) that asks the user to enter number 2. Multiply number 1 and number 2 together and print the answer. BONUS : Try to show number 1 and number 2 in the print statement (see practice task 3 to help you). Remember: Break up variables in a print line by using commas. When you run it, it could look something like this: Challenge Task 2 - Retirement Create a new Python program. Save is as ' 4-Retirement.py ' Add a comment at the top with your name and the date. Write an input line ( don't forget int ! ) that asks the user to enter their age. Print the year that they will turn 65. (This is slightly tricky. Hint : You need to know their age, and you need to know the current year. You need to subtract something, and you need to add something. Try using scrap paper to help you figure it out.) BONUS : Use only one print line. BONUS : Try to use only two lines in total . Remember: Break up variables in a print line by using commas. When you run it, it could look something like this: <<< #3 Inputs #5 Selection >>>

A simple HTML and CSS editor using Code Minrror libraries. Learn how to create simple web pages using HTML. Try practice tasks and learn through text and images. Perfect for students learning GCSE Computer Science in UK schools. Simple HTML & CSS Editor This page is under active development.

Learn about the four logical operators - NOT, AND, OR and XOR - and truth tables. Based on the 2020 Eduqas (WJEC) GCSE specification. 2.1: Logical Operators & Truth Tables Exam Board: Eduqas / WJEC Specification: 2020 + What is a logical operator? Inside of each computer system are millions of transistors . These are tiny switches that can either be turned on (represented in binary by the number 1 ) or turned off (represented by 0 ). Logical operators are symbols used to represent circuits of transistors within a computer. The four most common operators are: NOT AND OR XOR What is a truth table? A truth table is a visual way of displaying all possible outcomes of a logical operator. The input and output values in a truth table must be a Boolean value - usually 0 or 1 but occasionally True or False. NOT A NOT logical operator will produce an output which is the opposite of the input . NOT is represented by a horizontal line . Boolean Algebra Notation written as NOT A A Truth Table AND An AND logical operator will output 1 only if both inputs are also 1 . AND is represented by a full stop. Boolean Algebra Notation written as A AND B A.B Truth Table OR An OR logical operator will output 1 if either input is 1 . OR is represented by a plus. Boolean Algebra Notation written as A OR B A+B Truth Table XOR An XOR (exclusive OR) logical operator will output 1 if the inputs are different and output 0 if the inputs are the same . XOR is represented by a circled plus. Boolean Algebra Notation written as A XOR B A B Truth Table Multiple Operations Exam questions will ask you complete truth tables that use more than one logical operator . Work out each column in turn from left to right and look carefully at which column you need to use. Simplification You may be asked to use a truth table to simplify an expression . This is actually really easy. Once you've completed the truth table see if any columns match the final expression . A+B and A+(A+B) both result in the same values , therefore: A+(A+B) can be simplified as just A+B. Q uesto's Q uestions 2.1 - Logical Operators: 1. Copy and complete the following truth tables: 1b. Simplify the expression in the second truth table. 2a. A cinema uses a computer system to monitor how many seats have been allocated for upcoming movies. If both the premium seats and the standard seats are sold out then the system will display a message. State the type of logical operator in this example. 2b. For the more popular movies, the cinema's computer system will also display a message if either the premium seats or the standard seats have exclusively been sold out. However, it will not output a message when both have been sold out. State the type of logical operator in this example. 1.6 - Additional Hardware 2.2 - Boolean Algebra Theory Topics

Learn about how to write algorithms, including pseudocode and the different flowchart symbols. Based on the 2020 Eduqas (WJEC) GCSE specification. 8.3: Writing Algorithms Exam Board: Eduqas / WJEC Specification: 2020 + Pseudocode Reminder Generally, pseudocode can be written in any way that is readable and clearly shows its purpose. However, the Eduqas exam board advises that pseudocode for the programming exam should follow the conventions below : Annotation { Write your comment in curly brackets} Define data type price is integer firstname is string Declare a variable's value set price = 100 set firstname = "Marcella" Input / output output "Please enter your first name" input firstname Selection (must have indentation) if firstname = "Steven" then output "Hello" + firstname elif firstname = "Steve" then output "Please use full name" else output "Who are you?" end if Iteration (while loop) while firstname ! = "Steven" output "Guess my name." input firstname repeat Iteration (for loop) for i in range 10 input item next i Define a subroutine Declare Sub1 [Subroutine content indented] End Sub1 Call a subroutine call Sub1 Writing Algorithms In an exam you may be asked to write an algorithm using pseudocode . Previous exams have offered up to 10 marks for a single algorithm . While this may seem daunting, it means you can still gain marks for an incomplete program , so don't leave it blank no matter what! You must decompose the problem and break it down into more manageable chunks . Here's an example question : “A teacher is marking tests. Write an algorithm that allows the teacher to input the number of tests to mark and then the mark of each test. Output the average mark, highest mark and lowest mark. The tests are marked out of 100.” This specific algorithm can be broken down into pre-code and three main parts : Part 0: Declare and assign variables. Part 1: Input the number of tests to mark. Part 2: Input the mark of each test. Part 3: Output the average, lowest and highest marks. Part 0: Variables Read the question carefully and work out the variables you will need in your algorithm. I have highlighted them in blue below: “A teacher is marking tests. Write an algorithm that allows the teacher to input the number of tests to mark and then the mark of each test . Output the average mark , highest mark and lowest mark . The tests are marked out of 100.” There is an additional variable to track as the average mark can only be worked out if we also know the total marks . number_of_tests is integer test_mark is integer average_mark is real highest_mark is integer lowest_mark is integer total is integer number_of_tests = 0 test_mark = 0 average_mark = 0 highest_mark = -1 lowest_mark = 101 total = 0 Before you write the actual program, you must declare the variables you will need and assign values to them. Firstly, declare the data type of each variable . A whole number is an integer and a decimal number is a real . The average must be a real data type because it is the result of division (total ÷ number_of_tests) and could be a decimal number . When assigning values, most numerical variables will be 0 . Most string values would be " " . However this question is a bit more complicated - the highest mark must start as a really low value and the lowest mark must start as a really high value . This is ensure the first mark entered becomes the highest and lowest mark - this will make sense later. Part 1: Input Number of Tests output “Enter the number of tests to mark: ” input number_of_tests After declaring and assigning your variables the next parts will depend on the algorithm you need to write. This example requires the user to input the number of tests . Part 2: Input Each Mark (Loop) for i = 1 to number_of_tests output “Enter the test mark: ” input test_ mark For part 2 we need the teacher to enter each test’s mark . This is best done as a loop as we do not know how many tests the teacher has to mark until they have typed it in (part 1). All code within the loop must be indented . if test_mark > highest_mark then highest_mark = test_mark endif if test_mark < lowest_mark then lowest_mark = test_mark endif We also need to work out what the highest and lowest marks are. This must be done within the loop as the test marks are entered. The test mark is compared to the current highest and lowest marks . If it is higher than the current highest mark it becomes the new highest mark . If it is lower than the current lowest mark it becomes the new lowest mark . This is why we set the highest_mark and lowest_mark to extreme values at the start - so the first mark entered becomes the new highest and lowest . total = total + test_mark next i The final steps of part 2 are to update the total marks and to close the loop . The total is increased by the test mark that has been entered. The ‘next i ’ command states that the current iteration has ended . The indentation has now stopped. Part 3: Outputs average_mark = total / number_of_tests output “The average mark is:” , average_mark output “The highest mark is:” , highest_mark output “The lowest mark is:” , lowest_mark Before the average can be output, it must be calculated by dividing the total by the number of tests . Then the average , highest and lowest marks can be output . Full Answer number_of_tests is integer test_mark is integer average_mark is real highest_mark is integer lowest_mark is integer total is integer number_of_tests = 0 test_mark = 0 average_mark = 0 highest_mark = -1 lowest_mark = 101 total = 0 output “Enter the number of tests to mark: ” input number_of_tests for i = 1 to number_of_tests output “Enter the test mark: ” input test_ mark if test_mark > highest_mark then highest_mark = test_mark endif if test_mark < lowest_mark then lowest_mark = test_mark endif total = total + test_mark next i average_mark = total / number_of_tests output “The average mark is:” , average_mark output “The highest mark is:” , highest_mark output “The lowest mark is:” , lowest_mark This example is slightly more complicated than some of the recent previous exam questions for writing algorithms. Remember to decompose the problem by identifying the variables you need first. Q uesto's Q uestions 8.3 - Writing Algorithms: 1. A violin player performs a piece of music 8 times . They record a score out of 5 how well they think they performed after each attempt. Write an algorithm using pseudocode that allows the violinist to enter the 8 scores and displays the highest score , lowest score and average score . An example score is 3.7. [10 ] 2. A cyclist wants a program to be made that allows them to enter how many laps of a circuit they have made and the time in seconds for each lap . For example they may enter 3 laps, with times of 20.3 , 23.4 and 19.8 seconds . The program should output the quickest lap time , slowest lap time , total amount of time spent cycling and the average lap time . Create an algorithm using pseudocode for this scenario. [10 ] 8.2 - Understanding Algorithms Theory Topics 8.4 - Sorting & Searching

Learn about different input and output devices, RAM (random access memory) and ROM (read only memory) and storage devices, including solid state, magnetic and optical types. Based on the OCR H446 Computer Science A-Level specification. Exam Board: OCR A-Level 1.3 - Input, Output & Storage Specification: Computer Science H446 Watch on YouTube : Input & output devices Storage devices RAM & ROM Virtual storage This topic covers the internal and external devices required to input data into computer systems , output from them and store data for both temporary and long-term use . Input & Output Devices Input devices , such as a keyboard , mouse , microphone or sensor , allow data to be entered into a computer system for processing . Input can be manual (e.g. typing on a keyboard ) or automatic (e.g. a temperature sensor taking readings ). Output devices , such as monitors , printers and speakers , present the results of processing in a form understandable to humans . Input and output are not limited to text - they may also be visual , audio or tactile (e.g. braille displays or printed paper ). Storage Devices Secondary storage is non-volatile storage used to permanently hold programs and data when not in use by the CPU . There are three types : Magnetic storage uses magnetised patterns on a disk or tape (e.g. hard disk drives or magnetic tape ) to store large amounts of data for a low cost per gigabyte . Solid-state storage uses flash memory with no moving parts (e.g. SSDs and USB drives ), making it very fast , durable and portable . Because there are no moving parts, it is the fastest to access data . Optical storage uses lasers to read and write data as pits and lands on a disc surface (e.g. CDs, DVDs, Blu-ray). Discs are cheap to mass produce , but they are not durable , slow to access and have a low capacity . RAM & ROM Primary storage is low-capacity , internal storage that the CPU can directly access . There are two types: Random Access Memory (RAM ) is volatile storage that temporarily holds both programs and data currently in use , including the operating system . It can be read from and written to , but all contents are lost when the power is turned off . Read Only Memory (ROM ) is non-volatile storage that normally cannot be changed . The contents of ROM are saved when the power is turned off . ROM stores the BIOS and firmware , including the instructions needed to boot the computer when it is switched on . Virtual Storage Virtual storage is the separation of logical storage from physical storage , such as when data is stored remotely and accessed over a network instead of being kept locally . A common example is cloud storage , where data is held on remote servers and accessed via the internet . Benefits are that it is scalable , enables easy collaboration , provides automatic backup and saves local storage space . Drawbacks include that it relies on a stable internet connection , poses security risks and reduces user control over data . Q uesto's K ey T erms Input & Output Devices Secondary Storage: magnetic, solid state, optical, portability, capacity, cost (per GB), access speed, reliability, durability, power consumption Primary Storage: RAM, ROM, volatile, non-volatile Virtual Storage: cloud storage D id Y ou K now? The first commercial hard disk drive , the IBM 305 RAMAC (released in 1956 ), was the size of two fridges , weighed around a tonne , and stored just 5 MB of data - about the same as one .mp3 song . 1.2 - Types of Processor A-Level Topics 2.1 - Systems Software

The most common errors made in Grennfoot when making a game and how to fix them, including when missing punctuation is expected or the end of file is reached while parsing. Common Greenfoot Errors Greenfoot Home If the world becomes greyed out and you can't click on anything then an error has occurred. The actor with the error will have red lines on it. When an error occurs, a red squiggly line will appear underneath the problem. Hover your mouse over the line and a helpful message will appear to help you solve the issue. Some of the more common errors (and how to fix them) are listed below: ; expected Every line with a white background must end in a semi colon ( ; ) ) expected You have missed a bracket . Count the number of open brackets and the number of closed brackets on a line and make sure you have an equal number of both. reached end of file while parsing You are missing at least one curly bracket ( } ) at the end of your program . Press enter to move onto a new line at the bottom; you must have a closed curly bracket with a yellow background and another closed curly bracket with a green background . cannot find symbol You have typed a command incorrectly . Greenfoot uses a system where commands have no spaces and each word after the first word is uppercase . Such as isKeyDown not IsKeyDown and not isKeydown. Check your spelling and capitals carefully. Stuck ? If you start typing but can't remember what commands come next, press Ctrl and Space together to show a list of all possible commands that you can use.

Learn about the characteristics of networks, protocols, standards, the internet, TCP/IP stack, DNS servers, protocol layering, LANs, WANs, packet and circuit switching, network security and threats, firewalls, proxies, encryption, network hardware, client-server and peer to peer networks. Based on the OCR H446 Computer Science A-Level specification. Exam Board: OCR A-Level 3.3 - Networks Specification: Computer Science H446 Watch on YouTube : Purpose of networks (LAN & WAN) Protocols & standards Protocol layering & TCP/IP stack Domain Name System (DNS) Packet & circuit switching Network security threats Network security protection Network hardware Client-server & peer-to-peer This topic looks at how data is transferred between computer systems on networks , including the required devices , protocols , network types and potential security threats . Purpose of Networks A network is a group of connected computers that can share data , resources and communicate with each other . The main purpose of a network is to allow users to share files , hardware (like printers ), internet connections and other services efficiently . A Local Area Network (LAN ) covers a small geographical area , such as a single building or school , and is usually owned and managed by one organisation . A Wide Area Network (WAN ) covers a large geographical area , connecting multiple LANs through public or leased communication lines such as the internet . YouTube video uploading soon Protocols & Standards Protocols are sets of rules that define how data is transmitted and received over a network , ensuring that devices can communicate reliably . Standards are agreed specifications that ensure different hardware and software systems are compatible and can work together . They are needed so that networks remain interoperable , secure and efficient , regardless of the devices or manufacturers involved . Common network protocols include: HTTP /HTTPS is used for transferring web pages over the internet . FTP aids the transfer of files across a network . SMTP is used to send emails and IMAP /POP receive emails . TCP/IP is the core suite of protocols that controls how data is packaged , addressed , transmitted and received across networks . YouTube video uploading soon Protocol Layering & TCP/IP Stack Protocol layering is used to divide complex networking tasks into manageable sections , making systems easier to design , understand and troubleshoot . It also allows different technologies or protocols to work together , as each layer only interacts with the ones directly above and below it. The four layers are: Application layer : Provides network services to end users , such as web browsing (HTTP ) or email (SMTP ). Transport layer : Manages data transmission between devices, ensuring it arrives reliably and in the correct order (e.g. TCP , UDP ). Internet layer : Handles addressing and routing of data packets between networks using IP (Internet Protocol ). Link layer : Manages the physical connection between devices and controls how data is transmitted over the network hardware . YouTube video uploading soon Domain Name System (DNS) The Domain Name System ( DNS ) translates human-readable domain names (like www.csnewbs.com ) into IP addresses that computers use to identify each other on a network . When a user enters a web address , the request is sent to a DNS server to find the matching IP address . If the server doesn’t have it stored locally , it queries other DNS servers higher in the hierarchy until it finds the correct address . The IP address is then returned to the user’s device , allowing it to connect to the correct web server to access the requested web page . YouTube video uploading soon Packet & Circuit Switching Packet switching and circuit switching are methods of data transmission , describing how data is sent across a network from one device to another . With packet switching , data is split into small packets , each sent independently across the network and reordered at the destination . This makes efficient use of network resources and allows many users to share the same connections . However, packets can arrive out of order or be delayed , causing variable performance . With circuit switching , a dedicated communication path is established between two devices for the duration of a session , as in traditional phone networks . It provides a reliable and consistent connection with guaranteed bandwidth . The drawback is that it wastes resources , as the dedicated line cannot be used by others . YouTube video uploading soon Network Security Threats There is a range of potential threats associated with network use to be aware of, including the following: Hackers can attempt to gain unauthorised access to computer systems or networks , often to steal , alter or destroy data . Viruses are malicious programs that attach themselves to other files and spread , potentially damaging or deleting data . Denial of Service ( DoS ) attacks overload a network or website with traffic , making it unavailable to legitimate users . Spyware secretly monitors user activity and collects information such as passwords or browsing habits . An SQL injection involves inserting malicious SQL code into a database query to access or alter sensitive data . Phishing uses fraudulent emails or messages to trick users into revealing personal information . Pharming redirects users from legitimate websites to fake ones designed to steal login details or financial information . YouTube video uploading soon Network Security Protection Minimising or preventing network threats is vital and can be achieved with the following measures : Firewalls monitor and control incoming and outgoing network traffic , blocking unauthorised access while allowing safe communication . Secure passwords help protect user accounts by making it difficult for attackers to guess or crack them, especially when they are long and complex . Anti-virus software scans and removes malicious programs , such as viruses and worms , before they can damage files or systems . Anti-spyware software detects and removes spyware , preventing it from secretly collecting personal or sensitive information from a user’s device . YouTube video uploading soon Network Hardware A range of network hardware is required for devices to transfer data to another location , including the following: A modem converts digital data into analogue signals and back , allowing internet access over phone or cable lines . A router directs data between networks and assigns IP addresses to connected devices . Cables provide the physical connections between devices . A Network Interface Card ( NIC ) enables a computer to connect to a network . A Wireless Access Point ( WAP ) allows wireless devices to join a wired network via WiFi . On a local area network ( LAN ), hubs broadcast data to all devices , whereas switches send data only to the intended destination , improving network efficiency . YouTube video uploading soon Client-Server & Peer-to-Peer A client–server network has a central server that provides resources and services to client computers . It allows for centralised management , making it easier to back up data and enforce security policies . However, it relies heavily on the server - if it fails , users may lose access to resources . A peer-to-peer (P2P ) network has no central server ; instead, each computer can act as both a client and a server , sharing resources directly . It is cheap and easy to set up , making it suitable for small networks . The drawback is that it can be less secure and harder to manage , as data and security depend on individual users . YouTube video uploading soon This page is under active development. Check here for the latest progress update. Q uesto's K ey T erms Purpose of networks: local area network (LAN), wide area network (WAN) Protocols: protocol, standard, protocol layers, TCP/IP stack, application layer, transport layer, internet layer, link layer DNS: Domain Name System Switching: packet switching, circuit switching Network security: hackers, viruses, unauthorised access, denial of service, spyware, SQL injection, phishing, pharming, firewalls, secure passwords, anti-virus, anti-spyware Network hardware: modem, router, cable, NIC, Wireless Access Points, hub, switch Client-server & peer-to-peer D id Y ou K now? The first computer worm is considered to be Creeper (in 1971 ), which spread across ARPANET computers and displayed the message: “ I’m the creeper, catch me if you can! ”. A second program called Reaper was then created to delete Creeper , making it arguably the first antivirus . 3.2 - Databases A-Level Topics 3.4 - Web Technologies