Year 8 Computing: Summer Assessment

A switch. It connects the devices within a single network and, unlike a hub, it sends each piece of data only to the device it is addressed to.

A for loop repeats a known number of times, such as exactly ten times or once for every item in a list, while a while loop keeps repeating for as long as its condition stays true. A while loop is the better choice when you do not know in advance how many repeats are needed, for example when asking the user for a password and continuing to ask until they type the right one.

The average is =AVERAGE(B2:B31) and the highest mark is =MAX(B2:B31). Both must start with an equals sign, otherwise the spreadsheet treats what has been typed as ordinary text, and both use a range written as the first cell, a colon, then the last cell.

Data is split into packets because sending one enormous file as a single lump would tie up the connection completely and everybody else would have to wait until it had finished. Small packets from different users can be interleaved, so everyone gets a share of the line. Splitting the data also makes the transfer far more reliable, because packets can take different routes to the destination and if one is lost or damaged only that single packet has to be sent again rather than the whole file. Each packet carries the destination address, the sender's address and a packet number so that the receiving computer can put them back in the right order.

The browser first asks a DNS server to look up the IP address that matches the name that has been typed, because computers route data by number rather than by name. The DNS server replies with an address such as 93.184.216.34. The browser then sends a request to the web server at that address. The server responds with the page, which is broken into packets that may travel by different routes and arrive out of order. The user's computer reassembles them in the correct order using the packet numbers, and the browser then renders the HTML and CSS into the page you see.

A relative reference such as B2 changes when the formula is copied, so copying it down one row makes it B3 and copying it right one column makes it C2. That is usually what you want, because a column of totals should refer to a different row each time. An absolute reference such as $B$2 has dollar signs that lock it, so it stays exactly the same wherever the formula is copied. An absolute reference is needed when every row has to refer to the same single cell, for example a VAT rate or a price per ticket stored once at the top of the sheet. Without the dollar signs the reference would slide down the sheet and the later rows would multiply by empty cells.

Alt text is the description written into the alt attribute of an image tag. Software that reads a page aloud, used by people who are blind or have very limited vision, reads the alt text in place of the picture, so it is the only way those users receive whatever the image is communicating. It also appears on the screen when the image itself fails to load, for example on a very slow connection. Without alt text the image is simply a gap, and any information it carried is lost, which is why alt text is treated as part of building an accessible site rather than as an optional extra.

A while loop keeps running for as long as its condition is true, and the condition is only rechecked at the top of each pass. If nothing inside the loop changes the variable that the condition tests, that condition can never become false, so the loop runs forever and the same value is printed over and over. The fix is to make sure something inside the loop changes the value being tested, such as adding the line count = count + 1 inside the loop so that count eventually reaches the limit and the loop stops.

numbers = [] to start with an empty list. Then for i in range(5): numbers.append(int(input('Enter a number: '))). The int is needed because input hands back text. Then print('The largest is', max(numbers)) and print('The average is', sum(numbers) / len(numbers)). Using len rather than typing 5 means the program still works if the number of values is changed later.

The HTML is <h1>Bike Club</h1>, then <p>We meet every Thursday after school and ride together for an hour.</p>, then <img src='bike.jpg' alt='A blue mountain bike leaning against a gate'>. The h1 element marks the most important heading on the page, the p element wraps the paragraph and must be closed, and the img element is self closing and needs a src attribute giving the file name plus an alt attribute describing what the picture shows.

The first measure is to keep regular backups of everything important, held separately from the main network so that the ransomware cannot encrypt them as well. If an attack succeeds, the school can wipe the affected machines and restore the files from the backup, which removes the entire point of the attack because there is no reason to pay for a key to data you already have. The second measure is to run anti malware software and to install operating system and application updates promptly. Anti malware scans files against known threats and removes them before they run, and updates close the security weaknesses that ransomware relies on to get in, since most successful attacks use flaws that were fixed months earlier.

The first reason is reuse. A calculation that is needed in six different places is written once as a function and then called six times, which makes the program considerably shorter and removes the repeated code. That also means a mistake in that calculation only has to be corrected in one place rather than hunted down in six, which is where most bugs in long programs come from. The second reason is that the program becomes far easier to read and to test. Each function has one clear job and a name that says what it does, so the main part of the program reads almost like English, and each function can be tested on its own before it is trusted in the finished program.

A wired connection is faster and far more consistent, because the data travels along a cable that nothing else is sharing, and it is more reliable since the signal is not weakened by distance, walls or interference from other equipment. It is also more secure, because an attacker would have to get into the room and physically plug in rather than simply being close enough to pick up a signal travelling through the air. Wireless has real advantages too. It is much cheaper and quicker to install because no cables have to be run through walls and floors, and it lets tablets and laptops be moved around the room or taken to another part of the school. For a room of fixed desktop computers that never move, the school should use wired connections, because speed, reliability and security matter more than mobility and the machines are staying where they are. A wireless access point should be added as well, so that visiting laptops and tablets can still connect.