Fundamentals of Information Technology - Operating Systems

An Operating System (OS) is an intermediary program between the user and the computer hardware.
Primary Goals: Ensure convenience for users (via GUI or CLI), enable efficient use of hardware (resource allocation), and facilitate problem-solving by executing user programs (Apps, Databases).
Structure: The system consists of Hardware (CPU, Memory, I/O), Operating Systems (coordination layer), Application Programs, and Users (people or machines).
Kernel vs. Shell: The Kernel is the core program running at all times, managing CPU and memory. The Shell is the user interface layer that interprets commands for the kernel.

Multi-user: Supports independent accounts for multiple users simultaneously.
Multitasking: Capable of running multiple applications at once.
Multiprocessing: Support for two or more CPUs.
Multithreading: Programs can be split into smaller parts loaded as needed for concurrent execution.
32-bit ( $x86-32$ ): Supports a maximum of $4\,GB$ of RAM and only $32-bit$ applications/OS.
64-bit ( $x86-64$ ): Backward compatible with $32-bit$ ; supports larger address spaces and both $32-bit$ and $64-bit$ software/hardware.

Windows 11 Minimums: $1\,GHz$ or faster processor ( $2$ or more cores), $4\,GB$ RAM, $64\,GB$ storage, DirectX 12, and Trusted Platform Module (TPM) $2.0$ .
Windows 10 Minimums: $1\,GHz$ processor, $1\,GB$ RAM ( $32-bit$ ) or $2\,GB$ ( $64-bit$ ), and $16\,GB$ ( $32-bit$ ) or $20\,GB$ ( $64-bit$ ) storage.
System Management Tools:
- System Properties: Handles computer name, hardware installation, and system restore.
- Task Manager: Monitors Applications, Processes, Services, Performance, Networking, and Users. In Windows 10, Applications/Processes are combined, and Networking is integrated into Performance.
- Migration Tools: User State Migration Tool (USMT), Windows Easy Transfer, and PCmover Express.

Bootstrap Program: Initial code stored in ROM or EPROM (firmware) that locates and loads the OS kernel.
Windows Boot Sequence: POST and BIOS check configuration in CMOS; BIOS reads the Master Boot Record (MBR), which identifies the Volume Boot Record (VBR) to load bootmgr.exe.
Interrupt Driven: The OS is interrupt-driven; hardware device controllers notify the CPU of completed operations via interrupts. A "trap" or "exception" is a software-generated interrupt.
System Calls: Interfaces used for process control (create/terminate), file management (open/read/write), device management, and protection.

Storage Hierarchy:
- Main Memory: Large, volatile, and directly accessible by the CPU.
- Secondary Storage: Non-volatile extension (HDD with magnetic tracks/sectors or faster SSD).
Units of Storage:
- $1\,byte = 8\,bits$
- $1\,KB = 1,024\,bytes$
- $1\,MB = 1,024^2\,bytes$
- $1\,GB = 1,024^3\,bytes$
- $1\,TB = 1,024^4\,bytes$
- $1\,PB = 1,024^5\,bytes$
Core Functions: Resource allocation for CPU cycles and memory, accounting for resource usage, and protecting information in multiuser environments.

Batch OS: Jobs with similar requirements are executed as grouped batches without direct user interaction.
Time-Sharing OS: Multitasking environment where the CPU is divided among multiple users to provide an interactive experience.
Distributed OS: Connects multiple computers via high-speed channels, allowing them to cooperate as a single entity (loosely coupled).
Network OS: Designed for file sharing and printer access over a LAN. Includes Peer-to-peer and Client-Server models.
Real-Time OS (RTOS): Used for time-critical tasks with precise timing.
- Hard Real-Time: Strict deadlines; response in milliseconds (e.g., satellite launch).
- Soft Real-Time: Fewer deadline restrictions (e.g., computer games).

Virtualization: Allows running guest OSes within a host OS using a Virtual Machine Manager (VMM), such as VMware or Virtualbox.
Cloud Computing: Delivers services over a network (Public, Private, or Hybrid).
- SaaS: Software as a Service (e.g., word processors).
- PaaS: Platform as a Service (e.g., database servers).
- IaaS: Infrastructure as a Service (e.g., storage/servers).
Open-Source: Source code is freely available (e.g., GNU/Linux, BSD UNIX). Supported by the Free Software Foundation (FSF) under the GNU Public License (GPL).
Debugging: Finding/fixing bugs using log files, core dumps (application failure), and crash dumps (kernel failure).