GCSE Computer Science Paper 2: Computing Concepts

1011 0101 = 128 + 32 + 16 + 4 + 1 = 181. 200 = 128 + 64 + 8 = 1100 1000. B is 1011 and 7 is 0111. 0110 is 6 and 1110 is E: 6E.

Each hexadecimal digit stands for exactly four bits, so a byte is two hex digits instead of eight binary digits. That makes values much easier for people to read and remember, and fewer mistakes are made when copying them.

Adding column by column, carrying where needed, gives 1000 0110. Check in denary: 45 + 70 + 19 = 134, and 134 = 128 + 4 + 2.

Every bit moves three places left and zeros fill the gap on the right: 1011 0000.

Each place shifted left doubles the number, so three places multiply it by 2 x 2 x 2 = 8: 22 becomes 176.

3 terabytes is 3,000 gigabytes. 40,000 megabytes is 40 gigabytes and 900,000 kilobytes is 0.9 gigabytes.

The letters have consecutive codes: A 65, B 66, C 67, D 68, E 69, F 70, G 71, H 72.

ASCII uses 7 bits, so it has only 128 codes, enough for English. Unicode uses more bits for each character, so it can represent over a million characters, including every writing system in the world and emoji.

400 x 300 x 8 = 960,000 bits. 960,000 / 8 = 120,000 bytes. 120,000 / 1000 = 120 kB.

20,000 x 8 x 5 = 800,000 bits. 800,000 / 8 = 100,000 bytes.

The pattern is five 0s, three 1s, six 0s and two 1s: 5 0, 3 1, 6 0, 2 1.

Reading from the root: N is right then left, 10. S is right, right, right, 111.

A: 3 x 1 bit = 3. N: 2 x 2 bits = 4. B: 1 x 3 bits = 3. S: 1 x 3 bits = 3. 3 + 4 + 3 + 3 = 13 bits.

BANANAS has 7 characters, so 7-bit ASCII needs 7 x 7 = 49 bits. 49 - 13 = 36 bits saved.

Q is 1 only when C is 0 and at least one of A and B is 1.

XOR, exclusive OR, outputs 1 when exactly one input is 1.

H = S AND NOT W, written H = S · W̄ in Boolean notation.

The ALU calculates and compares, the control unit coordinates, the clock keeps time, and registers hold the values being worked on.

The CPU fetches the next instruction from main memory, using the address held in the program counter. The control unit decodes the instruction to work out what it means. The instruction is then executed, and the cycle repeats with the next instruction.

A laptop gets carried around and knocked, and an SSD has no moving parts to damage. It is also faster, lighter and uses less power than a hard disk, so the laptop starts and loads quickly and its battery lasts longer.

A compiler translates everything first, an interpreter translates and runs line by line, and an assembler translates assembly language.

High-level languages use English-like keywords, so programs are quicker to write and much easier to read and debug. They are also portable: the same program can be translated for different types of processor, whereas low-level code is written for one processor.

An embedded system, such as the controller in a washing machine, is part of a larger device and does one job.

A PAN connects one person's devices, such as a phone and headphones over Bluetooth.

HTTPS is an application protocol, TCP works at the transport layer, IP at the internet layer and Ethernet at the link layer.

SMTP is used to send email: it transfers a message from the sender's device to their mail server and on to the recipient's server. IMAP is used to retrieve email: it lets a device read the messages that are kept on the server, so they stay in step across devices.

Every network interface has a unique MAC address. The router keeps a list of the MAC addresses that are allowed, and refuses to connect any device whose address is not on the list.

Wireless gives freedom to move. Wired connections are usually faster, more secure and less affected by interference.

Inventing a scenario to get information is blagging, watching someone is shouldering, and fake emails are phishing.

A virus copies itself into other files, a trojan is disguised as something useful, and spyware secretly gathers information.

Black-box testing simulates an attack from outside: the testers are given no knowledge of the system and no login details. White-box testing simulates a malicious insider, such as an employee, who knows how the system works and has basic login details.

Software updates include patches that close security weaknesses that have been discovered. Installing them automatically means the computer is protected as soon as the fix is released, before attackers can exploit the weakness, and does not depend on the user remembering to update.

A CAPTCHA asks for something that people find easy and automated programs find hard, which stops bots.

FilmID uniquely identifies each film, so it is the primary key of Film. Showing uses FilmID to link each showing to a film, so in Showing it is a foreign key.

Each clause earns its own mark. DESC puts the largest year, the newest film, first.

SELECT Title, Year
FROM Film
WHERE Genre = 'Sci-fi'
ORDER BY Year DESC

The two tables are linked by matching FilmID in each, so every showing is paired with its own film. Without that condition every showing would be paired with every film.

SELECT Title, StartTime
FROM Film, Showing
WHERE Film.FilmID = Showing.FilmID
AND Screen = 2

Without the WHERE clause, every film's running time would be set to 112.

UPDATE Film
SET Minutes = 112
WHERE FilmID = 3

The values go in the same order as the fields, ShowID, FilmID, Screen, StartTime, with the time in quotes because it is text.

INSERT INTO Showing
VALUES (106, 3, 1, '19:30')

Smart speakers are always listening for their wake word, which raises obvious privacy concerns: recordings of private conversations can be stored on the company's servers, and the data gathered about a household can be used to target advertising. Legally, the company must follow the Data Protection Act 2018, processing personal data lawfully, keeping it secure, not keeping it for longer than needed and letting users see what is held about them. Poorly secured devices could also be hacked to listen in or to reach the rest of the home network, which is an offence under the Computer Misuse Act 1990. On the other hand, voice control is a real benefit for people who are blind, disabled or elderly, helping them live independently. Environmentally, the devices are always on, and every request is processed in energy-hungry data centres; making them uses mined materials, and old devices add to e-waste. On balance smart speakers are useful, especially for accessibility, but users should review privacy settings and companies must handle the data responsibly.