unit 5 cs

The Need for an Operating System

• Early computers before the 1970s lacked operating systems, requiring control software to be loaded via paper tape or punched cards at startup.
• In the 1970s, home computers stored a partial OS in a ROM chip and loaded the rest via cassette tape.
• The development of hard disk drives led to operating systems being stored on HDDs.
• BIOS (Basic Input/Output System) handles motherboard startup, originally stored on ROM chips but now stored in flash memory, with settings in CMOS memory.
• Modern OS are partially loaded into RAM providing an application environment, user interface (HCI), and hardware abstraction.
• Examples include Microsoft Windows, Apple Mac OS, Google Android, and iOS.

Human-Computer Interfaces (HCI)

• Command Line Interfaces (CLI) require users to type precise, text-based commands, offering full control but are slower.
• Graphical User Interfaces (GUI) use icons, windows, menus, and pointing devices for interaction.
• The first common GUI was WIMP (Windows, Icons, Menus, Pointing device).
• Post-WIMP interfaces include touchscreens on smartphones, tablets, and modern PCs.
• These use fingers/stylus for actions like tapping, pinching, and rotating, providing more intuitive and flexible interaction.

Memory Management

• Handles computer’s main memory, optimizing by allocating/deallocating memory for running applications
• It tracks allocated and free memory, and swaps data between RAM and HDD/SSD.
• Memory allocation can be single (one application uses all memory), partitioned (variable-size blocks), paged (fixed-size partitions), or segmented (non-contiguous blocks).
• Memory protection prevents multiple applications from using the same memory location, ensuring security and preventing data corruption

Security Management

• Ensures data integrity, confidentiality, and availability through OS updates.
• It keeps antivirus and security software up to date, using firewalls to monitor network traffic.
• It also manages user privileges (passwords, user IDs), controls access rights to files and directories, offers data recovery options, and prevents unauthorized access

Process Management

• Manages running programs (processes) by allocating resources efficiently and synchronizing processes through scheduling, conflict resolution, and queuing.

Hardware Management

• Controls all input and output (I/O) devices, ensuring smooth operation.
• Uses device drivers to communicate with hardware, translating data into a format understandable by I/O devices.
• It prioritizes hardware resource allocation and manages queues & buffers (e.g., printing), loading printer drivers, and handling errors.

File Management

• Manages files and directories, defining file naming standards (e.g., .docx, .txt, .xls).
• It performs file operations (create, open, close, delete, rename, copy, move), maintains directory structures, enforces file access control, specifies file storage formats (e.g., FAT, NTFS), and allocates memory for file access.

Types of Utility Software

• Hard Disk Formatter prepares an HDD for use by creating partitions and writing directory data/TOCs, using file systems like NTFS; full formatting erases all data.
• It detects/repairs bad sectors, where hard bad sectors are physical damage and soft bad sectors are software errors.
• Virus Checkers protect against malware via background scanning, comparing files against virus databases, heuristic analysis, and quarantine systems, requiring regular updates.
• Defragmentation Software reorganizes fragmented files on HDDs into contiguous sectors, improving speed, but is not needed for SSDs.
• Disk Content Analysis & Repair Software analyzes disk usage, removes unnecessary files, and flags/replaces bad sectors.
• Disk & File Compression reduces file size (file compression) or compresses data before writing to disk (disk compression); compressed files need decompression.
• Back-Up Software protects files by allowing scheduled backups of modified files, with a 3-version strategy: current, local, and remote backup.
• Windows File History backs up files hourly, retaining past versions, and Mac OS Time Machine performs hourly, daily, and weekly backups, deleting old backups when storage is full.

Static Libraries

• Code is embedded at compilation, increasing program size but ensuring all necessary routines are included.

Dynamic Libraries (DLL – Dynamic Link Library)

• Routines are linked at runtime, saving RAM and processing power.
• Multiple applications can share the same library file, improving efficiency.

Example: Using DLL in a Program

• When software with printer functionality prints a document, the program accesses the printer routine from the DLL dynamically, reducing memory usage and speeding up execution.

Purpose of Translators

• Converts source code into machine code for execution in a computer’s main memory.

Assemblers (For Assembly Language)

• Converts assembly language into machine code, which can be stored for immediate execution or saved for later use.
• Assembly code is machine dependent and used for speed-critical applications like OS components, robotics, and embedded systems.

Compilers & Interpreters (For High-Level Languages)

• Compilers translate entire source code into machine code before execution, generating an object program that requires recompilation only when changes are made.
• Interpreters execute source code line by line without producing a stored machine code file, resulting in slower execution.

Portability

• Assembly Language is machine dependent (not portable).
• High-Level Languages are machine independent (portable).

Partial Compiling and Interpreting

• Achieves shorter execution times by partially compiling and interpreting source code.
• The compiler translates source code into low-level, machine-independent intermediate code (bytecode), which is then interpreted by an interpreter.

Key Features of an IDE

Source Code Editor

• Allows programmers to write and edit code within the IDE, improving efficiency.
• Has syntax highlighting, auto-completion, dynamic syntax checking, and code folding.

Compiler & Interpreter

• IDEs provide either a compiler to create an executable file or an interpreter to run code line-by-line.

Run-Time Environment & Debugger

• Debugger helps detect and fix errors, with single-stepping, breakpoints, and displays variable values.

Auto-Documenter

• Generates documentation for the program, explaining the function and purpose of different parts of the code.