GCSE Computer Science - Unit 3 (Computers)

What is the 'Stored Program Concept'?

A concept where both program instructions and data are stored in the same memory. This was a breakthrough that allowed computers to be reprogrammed for many different tasks.

 What is the difference between Computer Architecture and Von Neumann Architecture?

• Computer Architecture: The overall structure of a computer system (hardware and how it works together).

• Von Neumann Architecture: A specific type of architecture based on the Stored Program concept.

What are the 5 key features of Main Memory (RAM)?

1. Short-term: Only holds data the CPU is currently using.

2. Addressable: Every location has a unique address.

3. Random Access: Data can be read/written in any order.

What are the 5 key features of Main Memory (RAM)?

4. Primary Storage: The CPU has fast, direct access to it.

5. Volatile: All content is lost when the power is turned off.

What are the main components of the CPU?

• Control Unit (CU)

• Arithmetic Logic Unit (ALU)

• Registers

• Cache

• Clock

What do the Control Unit (CU) and Arithmetic Logic Unit (ALU) do?

• Control Unit (CU): Fetches, decodes, and manages the execution of instructions.

• Arithmetic Logic Unit (ALU): Performs all math (add, subtract) and logic (AND, OR, NOT) calculations.

 What are CPU Registers?

Small, extremely fast storage locations within the CPU that hold instructions, intermediate results, and data that is being worked on immediately.

What is CPU Clock Speed?

The rate at which a tiny quartz crystal in the CPU vibrates, triggering actions. It's measured in Hertz (Hz). A higher clock speed means more instructions can be executed per second.

What is the purpose and direction of the three main computer buses?

• Address Bus: Carries a memory address from the CPU to RAM. It is unidirectional (one-way).

• Data Bus: Transfers data and instructions between the CPU and RAM. It is bidirectional (two-way).

• Control Bus: Carries signals to coordinate actions. It is bidirectional (two-way).

What is Bus Width?

The number of wires or connections on a bus. A wider bus can carry more data at once. For an address bus, a wider bus means the CPU can access more memory locations.

What are the three stages of the Fetch-Decode-Execute cycle?

1. Fetch: The CPU gets the next instruction from RAM.

2. Decode: The Control Unit figures out what the instruction means using the CPU's instruction set.

3. Execute: The instruction is carried out by the relevant component (e.g., the ALU).

What are the specific steps of the 'Fetch' stage?

1. The CPU places the memory address of the next instruction on the address bus.

2. The Control Unit sends a 'read' signal along the control bus to memory.

3. The content from that memory location is sent along the data bus to the CPU.

 What is the difference between primary (Main) and secondary storage?

• Primary (RAM): Volatile, fast, smaller, directly accessed by CPU.

• Secondary (HDD, SSD): Non-volatile (long-term), slower, larger. Programs must be loaded from it to RAM for use.

 How do the three main types of storage write data?

• Magnetic (HDD): A read/write head magnetises a spinning platter to store 0s and 1s on concentric tracks, which are split into sectors.

• Optical (CD/DVD): A laser burns tiny pits (less reflective, 0) and lands (more reflective, 1) onto a disc.

• Solid-State (SSD): Transistors trap electrons in pools. A full pool is a 0, an empty pool is a 1.

How do the three main types of storage read data?

• Magnetic (HDD): The read/write head detects the magnetic state (North or South) of each spot on the platter.

• Optical (CD/DVD): A laser is shone on the disc. A light sensor detects if light is reflected strongly (a land, 1) or dimly (a pit, 0).

• Solid-State (SSD): A small voltage is applied. If the transistor turns on, the pool is empty (a 1). If it stays off, the pool is full (a 0).

What is an Embedded System?

A small computer on a chip, built into a larger device to perform a single, dedicated task, often in real-time (e.g., the computer in a washing machine, an anti-lock braking system, or an insulin pump).

What are common features of an embedded system?

 They are designed for a specific task, have limited memory and processing power, use low power, are small, and have a minimal user interface.

 What is the Internet of Things (IoT)?

A network of physical objects that have embedded systems and wireless tech to collect and share data with each other, with little or no human interaction.

What are the 5 main jobs of an Operating System (OS)?

1. Process Management

2. Memory Management

3. File Management

4. Peripheral Management

5. User management

How does the OS manage Processes and Files?

• Process Management: It uses a scheduling algorithm to allocate CPU time and memory to each running program.

• File Management: It keeps track of files, which are often stored in a hierarchical tree structure (folders inside folders).

How does an OS manage memory when RAM gets full?

 It uses virtual memory. Inactive processes are moved from RAM to a designated space on the hard drive. This process is managed using a paging algorithm.

How does the OS manage users?

Through access control (logins and passwords), providing a user interface (GUI or command line), and managing file permissions (who can read, write, or delete files).

What is Utility Software?

Small programs that perform specific maintenance tasks for the computer system

What does Data Compression software do?

 It reduces the size of a file so it takes up less storage space and is faster to transfer across a network.

What does File Repair software do?

It scans a corrupted or damaged file, extracts as much data as it can, and saves it into a new, usable file.

 What does Disk Defragmentation software do?

 It speeds up file access on magnetic hard drives by rearranging the scattered parts of files so they are stored in adjoining blocks on the disk.

 What does Backup Software do?

 It makes a copy of your files at regular intervals. If the original files are lost or damaged, the backup copy can be restored.

How does anti-malware software work?

 It uses two main methods:

1. Signatures: It scans files for patterns (signatures) that match a database of known malware.

2. Behaviour Analysis: It monitors programs for suspicious behaviour (e.g., trying to stay in memory after closing).

What does it mean for software to be "Robust"?

A program is robust if it can handle unexpected user actions or errors without crashing, and is free from security vulnerabilities.

What are code vulnerabilities and bad programming practices?

• Vulnerabilities: Hidden weaknesses in code that could create a security risk.

• Bad Practices: Things like not planning for security, using quick fixes, writing messy code, and not testing enough, which can lead to vulnerabilities.

How can programmers make their software more robust?

• Good programming practices.

• Regular code reviews.

• Keeping an audit trail of changes.

• Using version control software.

 What is the difference between a High-Level and a Low-Level programming language?

• High-Level: Closer to human language, easier to write, has libraries of ready-made code (e.g., Python). One line of high-level code can become many lines of machine code.

• Low-Level: Closer to computer hardware (e.g., Machine Code, Assembly). The programmer must be familiar with the CPU's instruction set.

 What is Assembly Language?

•  A low-level language that uses mnemonics (short text codes) to represent machine code instructions. It has to be translated into machine code before it is executed.

What is an Assembler?

•  A program that translates assembly language into machine code. There is a one-to-one relationship (one assembly instruction translates to one machine code instruction).

What is a Compiler?

 Translates all the source code at once into a single executable file (object code) before running.

What is an Interpreter?

 Translates and runs the source code one line at a time, every time the program is run.