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UNIX is one of the most influential operating systems ever developed, forming the backbone of Linux, macOS, cloud servers, and enterprise systems. One of its greatest strengths is its simple, elegant, and powerful file system structure. This rewritten post explains file management, inodes, directories, system calls, links, IPC, processes, and memory management in UNIX , in a clear and modern style suitable for students, job seekers, and professionals. SECTION I – FILE MANAGEMENT IN UNIX 1. How UNIX Represents Devices In UNIX, everything is treated as a file . This includes keyboards, disks, terminals and other hardware components. All device files are stored inside the /dev directory and are classified as: ✔ Regular File A normal file that stores user data. ✔ Block Special File Represents block-oriented devices (like disks). Data transfers occur in blocks. ✔ Character Special File Represents character-based devices such as keyboards or serial ports, transferring data as a s...

Oracle PL/SQL is one of the most powerful procedural extensions to SQL ever built. It has shaped enterprise applications for decades and continues to be deeply integrated into Oracle databases, cloud offerings, and modern data engineering workloads. This extensive guide covers everything you need to know about PL/SQL —from basic concepts to advanced features like dynamic SQL, triggers, external procedures, file handling, roles, mutating tables, debugging, and best coding practices. 1. Introduction to Oracle PL/SQL What is PL/SQL? PL/SQL (Procedural Language/Structured Query Language) is Oracle’s extension to standard SQL. While SQL is declarative and designed for querying data, PL/SQL adds imperative programming capabilities such as: Variables & constants Conditional statements Loops Functions & procedures Packages Exception handling Object-oriented features (encapsulation, overloading, information hiding) It enables developers to write complex, da...