OCR COMPUTER SCIENCE ALL TOPICS

Types of magnetic storage

Hard disk drive, Floppy disk, Magnetic tape

Three examples of input devices

Keyboard, Mouse, Microphone, Barcode reader, Webcam, Magnetic stripe reader

Example of a device used for both input and output

Touchscreen

Name given to the areas on a CD’s surface burned into grooves by a laser

Pits

What does CD stand for?

Compact Disc

Three examples of output devices

Speaker, Monitor, Printer, Projector

Storage device with the highest typical storage capacity: CD, DVD, or Blu-Ray?

Blu-Ray

What is mounted at the end of the actuating arm in a hard disk drive?

Read/write head

Storage device with typical capacities in the range 500GB-5TB?

Hard disk drive

Two disadvantages of SSDs

High cost per GB, Limited lifespan

What does ROM stand for?

Read-only memory

Structure in which information is stored in flash memory

Information is stored in blocks, which are combined to form pages.

What is meant by non-volatile?

A non-volatile storage medium does not lose its information when power is lost.

Two types of logic gate used in flash storage

NAND and NOR

Three advantages of SSDs

High transfer speeds, Lightweight, No moving parts

Is ROM volatile or non-volatile?

Non-volatile

Form of storage device that uses silicon semiconductors to store information

Flash

Three disadvantages of CDs

Easily damaged by scratches, Relatively low capacities, Relatively slow transfer speeds

What is an operating system?

A collection of programs that work together to provide an interface between the user and computer.

Three functions of an operating system

Memory management, Security, Resource management, User interface, I/O management, Utility software, Interrupt management

Similarities and differences between paging and segmentation

Both: Used when RAM space is insufficient, can cause disk thrashing.
Paging: Uses equal-sized sections called pages.
Segmentation: Uses variable-sized, logical sections called segments.

How virtual memory is used when there is not enough RAM

A section of the hard drive is used to act as RAM. Sections of programs not currently being used are temporarily moved into virtual memory through paging, freeing up memory for other programs in RAM.

What is an interrupt?

A signal generated by software or hardware to indicate to the processor that a process needs attention.

Stages of the Interrupt Service Routine

1. Interrupt register checked at the end of each Fetch-Decode-Execute cycle.
2. If an interrupt exists with a higher priority, the current contents of the CPU registers are transferred into a stack.
3. The relevant interrupt service routine (ISR) is loaded into RAM.
4. A flag is set to signal the ISR has begun.
5. The flag is reset once the ISR has finished.
6. Interrupt register checked again. If interrupts are of a higher priority, the process is repeated.
7. If no higher priority interrupts, the contents of the stack are popped back into the special memory registers.
8. The Fetch-Decode-Execute cycle renews as before.

Are these scheduling algorithms pre-emptive or non-pre-emptive? FCFS, SRT, SJF, MLFQ, RR

Pre-emptive: RR, SRT, MLFQ
Non-preemptive: FCFS, SJF

Advantage and disadvantage of using Multilevel Feedback Queues for scheduling

Advantage: Services most urgent interrupts first.
Disadvantage: Hard to implement.

Define a real-time operating system and when it may be used

Real-time operating systems perform a task within a guaranteed time frame. They are used in systems where a response within a given time frame is critical, e.g., life support systems, self-driving cars, power systems.

Three functions of the BIOS

1. Running tests upon the computer’s start-up (POST).
2. Checking the CPU clock, memory, and processor.
3. Testing for external memory devices.

Role of a device driver

Enable the operating system to interact with hardware devices.

Instance in which a Virtual Machine may be used

Testing programs, Protection from malware, Running software compatible with different versions and types of operating systems.

Advantage and disadvantage of intermediate code

Advantage: Platform independent, portable.
Disadvantage: Slower execution.

Difference between applications and systems software

Applications software is utilised directly by the end-user, whereas systems software ensures the high performance of the computer.

Three examples of utilities

Compression, Automatic backup, Disk defragmentation, Automatic updating, Antivirus

Advantage of using closed source code

Thorough, regular, and well-tested updates; Expert support and user manuals from the company; High levels of security as it is developed in a professional, controlled environment.

Two features of open source code

Does not require a license to be used; Distributed with the source code; Can be modified and sold on.

Two advantages of using compiled code over interpreted code

Faster to execute; Does not require a compiler to run.

Two advantages of using interpreted code over compiled code

Platform independent; Runs instantly without waiting for compilation; Useful for debugging.

What is assembly language?

A low-level language that has almost a one-to-one relationship with machine code. It is platform specific.

Stages of compilation

Lexical analysis, Syntax analysis, Code generation, Optimisation.

What happens during syntax analysis?

Tokens are compared to the rules of the programming language; Syntax errors are identified; Symbol table updated with more details; Semantic analysis (finding logic errors).

Difference between static and dynamic linkers

Similarities: Both link external modules and libraries to the main program.
Static: Library code copied into the file. File size increased.
Dynamic: Addresses of libraries included within the file. External updates automatically feed through to the main program.

Three advantages of using libraries

Error-free; Save time; Re-usable; No need to ‘reinvent the wheel’; Designed by experts.

Function of a loader

Provided by the operating system, a loader retrieves the library or subroutine from the given memory location.

Purpose of the optimisation stage of compilation

Reduce execution time; Reduce inefficient sections of code; Remove redundant code.

Common stages of software development life cycles (SDLCs)

Analysis, Design, Development, Testing, Implementation, Evaluation, Maintenance.

Define white box testing

A form of testing carried out by software development teams in which the test plan is based on the internal structure of the program. All possible routes through the program are tested.

What is TELOS?

A method of analysis used by designers to evaluate the feasibility of a project. It considers technical, economic, legal, and operational aspects of the project, as well as scheduling.

What are agile methodologies?

A collection of methodologies that aim to improve the flexibility of software development. They respond quickly to changes in user requirements.

Advantages of waterfall programming methodologies

Straightforward to manage; Clear structure; Clearly documented.

Three disadvantages of extreme programming

High cost due to two people working on one project; Teamwork and good communication are essential; End-user must be present throughout the duration of the project.

Type of projects spiral programming methodologies are suited to

Large, risk-intensive projects with a high budget.

Type of projects Rapid Application Development (RAD) programming methodologies are suited to

Projects where high usability is required and user requirements may not be clear from the outset or are continually changing. Suited to small to medium-sized projects with a relatively low budget and short time-frame.

Define an algorithm

A set of instructions used to solve a problem.

Three key qualities of algorithms

Inputs must be clearly defined; Must always produce a valid output for any defined input; Must be able to deal with invalid inputs; Must always reach a stopping condition; Must be well-documented for reference; Must be well-commented so modifications can easily be made.

What are programming paradigms?

Different approaches to using a programming language to solve a problem.

Two broad categories programming paradigms are split into

Imperative; Declarative.

Advantages of procedural programming

Can be applied to a wide range of problems; Relatively easy to write and interpret.

Use of declarative programming

Expert Systems/Knowledge-based Systems; Artificial Intelligence.

Four main structures used in structured programming

Sequence; Selection; Iteration; Recursion.

How does assembly language differ from machine code?

Assembly language uses mnemonics rather than binary. One line in assembly language is equal to one line in machine code.

Function of the STA mnemonic

Storing the value in the Accumulator at the given memory address.

Function of the BRP mnemonic

Branches to a given address if the value in the Accumulator is positive. It is a conditional branch.

Function of the opcode and operand

The opcode specifies the instruction to be performed and the addressing mode. The operand holds a value related to the data on which the instruction is to be performed.

Four addressing modes

Immediate Addressing; Direct Addressing; Indirect Addressing; Indexed Addressing.

What is a class?

A template for an object that defines the state and behaviour of an object. An object is an instance of a class.

Disadvantage of Object-Oriented Languages

Requires a different style of thinking which can be difficult for programmers accustomed to other paradigms to pick up; OOP may not be suited to all types of problems; Generally unsuitable for smaller problems.

Name given to the public and private keys used in asymmetric encryption

Key pair

Two categories of compression

Lossy and lossless

Type of compression where the quality of a file is not degraded

Lossless

Purpose of encryption

To keep data secure during transmission

One type of lossless compression

Run length encoding, Dictionary encoding

Form of encryption where the sender and receiver share the same private key

Symmetric encryption

How many keys are used in asymmetric encryption?

Two (one public and one private)

If person A wants to send a message to person B using asymmetric encryption, which key should they use to encrypt the message?

B’s public key

What is said to have occurred when two keys map to the same hash?

A collision

Type of lossless compression where repeated characters are replaced by one occurrence and the number of times to repeat the character

Run length encoding

Name given to the process of turning an input into a fixed-size value

Hashing

Data structure that uses hashing to store information with constant lookup time

Hash table

What is meant by compression?

The process of reducing the space required to store a file

Two properties that a hashing algorithm should have

Low chance of collision; Quick to calculate; Output smaller than input

What is a relational database?

A database that recognises the difference between entities and uses different tables for each entity.

What is an entity?

An item of interest about which information is stored.

What is a flat file?

A database that consists of a single file, usually about one entity.

What is a primary key?

A unique identifier for each record in a table.

What is a foreign key?

The attribute which links two tables together.

What is a secondary key?

An index other than the primary key used to search and sort through the database with more convenience and speed.

What does capturing data mean?

The process of getting the information that will be stored in the database.

Method banks use to capture data from cheques

Magnetic Ink Character Recognition (MICR) is used for all details apart from the amount, which must be entered manually.

What does selecting data mean?

The process of removing excess information to extract only the data you require.

What does managing the data mean?

To manipulate the information collected in any type of way, such as through sorting or selecting certain parts using SQL.

Most common language used to manipulate data in databases

SQL (Structured Query Language)

What is a network?

Two or more computers connected together that transmit data.

What are protocols?

Sets of rules defining how two devices communicate with each other.

Why are protocols standard?

Protocols are standard so devices from different manufacturers don’t have problems communicating.

Structure of the Internet

The Internet is a global network of interconnected networks.

What does TCP stand for?

Transmission Control Protocol

What does IP stand for?

Internet Protocol

Function of the application layer during data transmission

Specifies what protocols need to be used to relate the application to what it’s being used for.

Role of the transport layer during data transmission

Establishes an end-to-end connection between the source and recipient computers. It also splits up the data into packets.

Role of the network layer during data transmission

Adds the source and destination IP addresses.