Cambridge International AS & A Level Computer Science: every topic, by paper

How many bytes are in a kibibyte (KiB)?

1024 bytes.

What is the difference between a kilobyte (kB) and a kibibyte (KiB)?

kB = 1000 bytes (denary prefix); KiB = 1024 bytes (binary prefix).

Convert 10110110 to hexadecimal.

1011 = B, 0110 = 6: B6.

Distinguish a LAN and a WAN.

LAN: a network over a small area such as a building. WAN: a network over a large geographical area.

Compare client–server and peer-to-peer networks.

Client–server: a central server provides resources and security. Peer-to-peer: each computer shares resources equally, with no central control.

Name three network topologies.

Bus, star and mesh (also hybrid).

Distinguish RAM and ROM.

RAM is volatile read/write memory; ROM is non-volatile and read-only.

Compare SRAM and DRAM.

SRAM uses flip-flops, is faster and needs no refreshing (used in cache); DRAM uses capacitors, is cheaper and denser but must be refreshed.

Distinguish PROM and EPROM.

PROM can be programmed once; EPROM can be erased with UV light and reprogrammed.

What is the von Neumann architecture?

A stored-program design in which instructions and data share the same memory and buses.

What is the role of the program counter (PC)?

Holds the address of the next instruction to be fetched.

What is the role of the MAR and MDR?

MAR holds the address being read or written; MDR holds the data or instruction being transferred.

What is an operating system?

Software that manages hardware and resources and provides a user interface and platform for applications.

Give four key management tasks of an operating system.

Memory management, file management, process management, security and hardware (device) management.

What is a utility program?

Software performing maintenance tasks, e.g. disk defragmenter, virus checker, backup, file compression.

Distinguish security, privacy and integrity of data.

Security: protecting data from loss or unauthorised access. Privacy: keeping personal data confidential. Integrity: data remain accurate and consistent.

What is a firewall?

Hardware or software that monitors and filters incoming and outgoing traffic against rules.

Name three types of malware.

Virus, worm, spyware (also trojan, ransomware).

What is a primary key?

A field (or fields) that uniquely identifies each record in a table.

What is a foreign key?

A field in one table that is the primary key of another, creating a relationship.

Give two limitations of a flat-file database.

Data redundancy (the same data repeated), which leads to inconsistency when not every copy is updated; and data dependency, so changing the file structure means changing the programs that use it.

What is an algorithm?

A sequence of steps to solve a problem.

What is abstraction?

Removing unnecessary details to focus on what matters for the problem.

What is decomposition?

Breaking a problem into smaller, more manageable sub-problems.

What is an array?

A fixed-size, indexed collection of elements of the same data type.

Give the pseudocode to declare a 1D integer array of 10 elements.

DECLARE Scores : ARRAY[1:10] OF INTEGER

What is a record?

A composite data type grouping related fields of different types.

Name the three basic programming constructs.

Sequence, selection and iteration.

Distinguish a count-controlled and a condition-controlled loop.

Count-controlled repeats a fixed number of times (FOR); condition-controlled repeats until or while a condition holds (REPEAT/WHILE).

Distinguish pre-condition and post-condition loops.

Pre-condition (WHILE) tests before each iteration and may run zero times; post-condition (REPEAT … UNTIL) runs at least once.

Name the stages of the program development life cycle.

Analysis, design, coding, testing and maintenance.

Compare the waterfall and iterative models.

Waterfall: each stage completed in sequence before the next. Iterative: develop in repeated cycles, refining the product each time.

What is rapid application development (RAD)?

Developing prototypes quickly with user feedback, with less emphasis on detailed planning.

What is a user-defined data type?

A type defined by the programmer from built-in types, e.g. records, enumerated types, pointers, sets.

What is an enumerated type?

A type with a fixed list of named values, e.g. TYPE Season = (Spring, Summer, Autumn, Winter).

What is a pointer type?

A type that stores the memory address of a variable of a given type.

What is a protocol?

A set of rules governing how data are transmitted between devices.

Name the four layers of the TCP/IP stack.

Application, transport, internet (network) and link.

What does the transport layer do?

Splits data into packets, adds port numbers and sequence numbers, and handles reliable delivery (TCP).

Simplify A + A.

A.

State De Morgan's laws.

NOT(A AND B) = NOT A OR NOT B; NOT(A OR B) = NOT A AND NOT B.

Simplify A.(A + B).

A (absorption).

What is multitasking?

The OS shares processor time between several processes so they appear to run at once.

Name the three main process states.

Running, ready and blocked.

What is a process control block?

A data structure storing a process's state, registers, priority and memory information.

What is encryption?

Scrambling plaintext into ciphertext using a key so it cannot be understood without the key.

Describe symmetric encryption.

The same secret key is used to encrypt and decrypt.

What is the main problem with symmetric encryption?

The key must be shared securely; if intercepted, messages can be read.

What is artificial intelligence?

The ability of a computer to perform tasks that normally need human intelligence.

What is machine learning?

Systems that improve their performance on a task by learning from data rather than explicit programming.

Distinguish supervised and unsupervised learning.

Supervised: learns from labelled data. Unsupervised: finds patterns in unlabelled data.

What is recursion?

A subroutine that calls itself.

What two parts must a recursive subroutine have?

A base case that stops the recursion and a general case that calls itself with a smaller problem.

Write a recursive function for factorial in pseudocode.

FUNCTION Fact(N : INTEGER) RETURNS INTEGER; IF N = 0 THEN RETURN 1 ELSE RETURN N * Fact(N − 1) ENDIF; ENDFUNCTION