AND questions

Virtual memory is a memory management technique that creates an illusion of a larger physical memory by using disk space. It allows for more efficient memory utilization and process isolation. For example, a system with 4GB RAM can use virtual memory to handle more data by paging to disk.

Paging is a memory management scheme that eliminates the need for contiguous allocation of physical memory. It divides memory into fixed-size pages and maps them to physical memory frames. This allows for efficient and flexible memory use, as pages can be loaded and swapped as needed.

A semaphore is a synchronization primitive used to control access to shared resources by multiple processes. It consists of a counter and operations (wait and signal) to manage resource allocation. For example, semaphores can prevent race conditions in concurrent programming by ensuring mutual exclusion.

A program is a static set of instructions stored on disk, whereas a process is a dynamic entity that executes the program's instructions. A program becomes a process when it is loaded into memory and executed. For example, a word processor application (program) runs as a process when opened.

A file system manages the storage and retrieval of files on a disk. It organizes files into directories and handles metadata such as file size and permissions. For example, NTFS in Windows and ext4 in Linux are file systems that manage data storage and access.

A race condition occurs when the outcome of a process depends on the sequence or timing of uncontrollable events. It can lead to unpredictable results. To prevent race conditions, synchronization mechanisms like mutexes and semaphores are used to ensure orderly access to shared resources.

A file descriptor is an integer handle used by the OS to access files and I/O resources. It is returned by system calls like 'open' and used in subsequent operations such as 'read' or 'write'. For example, in Unix-like systems, file descriptor 0 refers to standard input.

Interrupt requests (IRQs) are signals sent to the CPU indicating that a device needs attention. IRQs help manage hardware communication and prioritize tasks. For instance, pressing a key on the keyboard generates an IRQ to notify the OS to read the keystroke.

A firewall is a network security system that monitors and controls incoming and outgoing network traffic based on predefined security rules. Its main purpose is to protect the network from unauthorized access. For example, a firewall can block suspicious traffic coming from the internet to protect your computer from malware.

A database is an organized collection of structured data stored electronically. Databases allow for efficient storage, retrieval, and management of data. For example, a customer relationship management (CRM) system stores information about customers, allowing businesses to track interactions and analyze customer behavior.

A compiler is a program that translates source code written in a high-level programming language (such as C++ or Java) into machine code that a computer can execute. For example, the GNU C Compiler (GCC) compiles C code into executable machine instructions that the CPU can understand.

HTML5 is the fifth version of the HTML standard. It introduces new elements, attributes, and behaviors, enhancing the language's capability to create more dynamic and interactive web content. For example, `<article>` and `<section>` elements are used for better semantic structuring.

Semantic elements provide meaning to the web content, improving accessibility and SEO. Elements like `<header>`, `<footer>`, and `<article>` make the structure of web pages more understandable to both browsers and developers.

The `<section>` element represents a thematic grouping of content, typically with a heading. It's used to divide a webpage into logical sections. For instance, `<section>` can be used to group related content such as different articles or parts of a webpage.

The `<header>` element typically contains introductory content or navigational aids, like headings or logo. Conversely, the `<footer>` element usually contains metadata about the section it is in, such as copyright information or contact details.

npm (Node Package Manager) is the default package manager for Node.js, used to manage packages and dependencies in Node.js projects. Example: npm install installs dependencies, and npm init initializes a new project with a package.json file to manage those dependencies.

ES modules allow you to use JavaScript's import/export syntax in Node.js. Example: In an ES module, you can import another module using 'import { func } from './module.js';' instead of using 'require'. Node.js supports ES modules natively from version 12 onwards.

The 'require' function is used to import modules in Node.js, following the CommonJS module system. Example: To import the 'fs' module, you use 'const fs = require('fs');' to access file system operations like reading or writing files.

readFile reads the entire file into memory, which can be inefficient for large files, whereas createReadStream reads the file in chunks, making it more memory efficient. Example: Use fs.createReadStream() when reading large files to prevent memory overload.

Synchronous methods block the event loop until the operation is complete, while asynchronous methods allow the program to continue running while the operation completes in the background. Example: fs.readFileSync is synchronous, while fs.readFile is asynchronous, not blocking the event loop.

Middleware functions process requests before they reach route handlers. They can modify `req` or `res`, end the request-response cycle, or pass control. For example: `app.use((req, res, next) => { console.log('Request received'); next(); });` logs every request.

Synchronous errors are caught using try-catch blocks, while asynchronous errors should be handled with `.catch()` or async error-handling middleware. For example: `app.use(async (req, res, next) => { try { await asyncFunction(); } catch (err) { next(err); } });`.

A reducer is a pure function that takes the current state and an action as arguments, returning a new state. For instance, a user reducer might handle actions like 'ADD_USER' or 'REMOVE_USER' and return the updated user list.

Redux Thunk is a middleware that allows action creators to return a function instead of an action object. This enables handling asynchronous operations. For example, you can fetch data from an API and dispatch an action once the data is received.

Selectors are functions that extract specific pieces of state from the Redux store. They enhance performance and readability. For instance, a selector like 'getUserById' can retrieve a user by their ID, allowing components to access only the necessary data.