CS UNIT 5

• Software that manages computer hardware resources and provides services for application programs
• Forms a platform for running applications, acting as an intermediary between the user and the hardware

Operating System (OS) Needs

• Early computers lacked OS, requiring manual loading of control software via paper tape or punched cards
• Modern computers use BIOS (Basic Input/Output System) stored on a flash memory chip on the motherboard to initiate start-up
• OS is loaded into RAM (Random Access Memory) due to its large size; not fully loaded at once to optimize performance
• An OS provides an environment for applications to run, a user-friendly interface and abstracts the complexity of hardware

Interfaces

• HCI (Human-Computer Interface) facilitates interaction; GUI (Graphical User Interface) and CLI (Command-Line Interface) are common types
• CLI requires users to type commands, necessitating knowledge of commands and syntax
• GUI uses icons and visual elements for interaction, simplifying tasks
• WIMP (Windows, Icons, Menus, Pointing devices) was an early GUI environment.
• Post-WIMP interfaces incorporate touch screen technology, supporting actions like pinching and rotating

OS Tasks - Memory Management

• Composed of memory optimization, organization, and protection
• Optimizes memory allocation/deallocation during simultaneous application runs, tracking allocated and free memory; swaps data between RAM and storage to maintain optimization
• Includes single contiguous allocation, partitioned allocation, paged memory (fixed-size partitions used by virtual memory systems) and segmented memory (non-contiguous blocks)
• Memory protection prevents applications from using same memory locations simultaneously, avoiding data loss or crashes

Security Management

• Ensures integrity, confidentiality, and availability of data through OS updates, antivirus software, firewalls and user privileges
• Access rights management, data recovery mechanisms and prevention of illegal intrusions are included

Process Management

• Manages allocation of resources allowing processes to synchronize

Hardware Management

• Manages all I/O devices through device drivers
• Translates data, sets priorities for hardware resources and manages queues and buffers (e.g. Printer management includes loading printer driver, sending data to printer buffer/queue, sending control commands, and handling errors)

File Management

• Defines file naming conventions, specific tasks (create, open, delete, etc.), directory structures and access control mechanisms
• Includes specifying logical file storage format (FAT, NTFS) and memory allocation

Utility Software

• Programs provided with OS or installed separately (initiated by user; some run in background)

Disk Formatter Utility

• Initializes new HDDs, organizes storage space into partitions, and writes directory data and tables of content

Antivirus Software Utility

• Protects from virus attacks by checking files, comparing against virus database, heuristic checking (identifying potentially malicious behavior), quarantining infected files
• Requires regular updates due to new viruses

Defragmentation Software Utility

• Reorganizes sectors on HDD to store files in contiguous blocks, reducing read-write head movements and improving data access time

Disk Content Analysis Software Utility

• Checks disk drives for empty space and disk usage by reviewing files and folders, assisting in removal of unwanted files

Disk Compression Utility

• Compresses data before storage; decompresses when reading

Backup Software Utility

• Schedules file backups to external devices or cloud storage; includes data recovery, restore points and automated backups to chosen devices

Program Libraries

• Collections of pre-written routines for use in software development, saving time and cost
• Static Libraries: software is linked to executable code in the library at compilation (embedded directly)
• Dynamic Libraries: link to the routines at run time, called dynamic link library files (DLL)

DLL Pros

• Smaller executable code in the main program
• DLL files can be changed independently

DLL Cons

• Executable code is not self-contained
• Requires DLL linking software

Language Translators

• System software that translates source code into machine code

Assembler Translator

• Translates assembly language into machine code

Compiler Translator

• Translates high-level languages into machine code.

Interpreter Translator

• Directly executes high-level languages line by line.

Pros of Compiling

• Faster execution, no syntax errors

Cons of Compiling

• Difficult to debug, potential crashes

Pros of Interpreting

• Easier to debug, no crashes

Cons of Interpreting

• Slower execution, source code is not protected

Partial compiling and Interpreting

• Source code is checked and translated by a compiler into object code
• The compiled object code is a low-level machine independent code, called intermediate code, p-code or bytecode
• To execute the program, the object code can be interpreted by an interpreter or compiled using a compiler.

Integrated Development Environment (IDE)

• Aids program writing and development with source code editor; compiler, interpreter, and a debugger
• A source code editor allows a program to be written and edited without the need to use a separate text editor