Computer System Architecture Notes

Computer System Architecture

Introduction

  • General Concept: This lecture taught by Dr. Ayman AboElHassan at Cairo University covers the architecture of computer systems, focusing on different processor configurations and the processes that manage those systems.

  • Date: February 17, 2025

Single-Processor Systems

  • Definition: A single-processor system contains a general-purpose processor that executes one instruction at a time.

  • Assumption: During this course, we will assume a single-core processor.

Multiprocessor Systems

  • Definition: Involves two or more processors working together in the same system.

  • Features:

    • They share the same memory (RAM).

    • Each processor has its own private registers and local cache.

    • They can execute multiple programs simultaneously, increasing the processing speed.

Multicore Systems

  • Definition: A special type of multiprocessor system that contains two or more processors (cores) on a single chip.

  • Advantages:

    • More efficient than connecting multiple single-core chips.

    • On-chip communication is faster, leading to better performance in executing single programs.

  • Note: While all multicore systems are multiprocessor systems, not all multiprocessor systems are multicore systems.

Clustered Systems

  • Definition: Comprises two or more individual computer systems (nodes) that work together.

  • Characteristics:

    • They form a parallel loosely-coupled system.

    • Each node can either be a single processor or a multicore system.

    • Example Layout: Computer 1, Computer 2, …, Computer n connected via a communication network.

Bootstrapping

  • Definition: The process of initializing the hardware system by loading the operating system (OS) kernel into RAM.

  • Role of Boot Loader: Acts as a mini operating system to perform hardware tests and initialize components to locate the OS kernel for loading into RAM.

  • Multi-stage Boot Loader:

    • Contains a 1st stage (e.g., BIOS, UEFI) to load further boot processes into RAM.

    • Contains a 2nd stage that reads the OS kernel from disk/USB (e.g., BOOTMGR, GNU GRUB).

  • Initial Tests: Power-On Self-Tests (POST) verify CPU, BIOS integrity, RAM, and system buses.

BIOS/UEFI

  • BIOS/UEFI: Loads the Master Boot Record (MBR) into RAM from the disk.

  • UEFI Advantages:

    • Supports disk sizes greater than 2 TB.

    • Offers animations, mouse support, and faster booting.

    • Features secure boot functionality.

System Calls

  • Purpose: Provide an interface between user programs and OS services, enabling user programs to request services from the OS.

  • Modes: User programs run in User Mode while the OS operates in Kernel Mode.

  • Operation: When a program requests a service, it issues a system call, switching from user mode to kernel mode.

  • Execution: Uses trap instructions, transferring control to the OS kernel and managing system resources accordingly.

System Call Types

  • Categories:

    • Process Management

    • File Management

    • Directory Management

    • Device Management

    • Communication

    • Miscellaneous

CPU Utilization

  • Concept of Utilization: Utilization = Time Used / (Time Used + Time Wasted).

  • Prediction: Utilization can be predicted based on the number of programs waiting for I/O.

  • Example Calculation:

    • If n is the number of programs and p represents the percentage time waiting for I/O, CPU utilization can be computed as: CPU Utilization = 1 - p^n.

Processes

  • Definition of Processes: A process is the dynamic execution of a program, which includes the program code, current state, and the resources required for execution.

  • Process Elements:

    • Address Space, Code Segment, Data Segment, Stack Segment, and system resources.

  • Process States: A process can be in a Running, Ready, or Blocked state, based on its execution requirements.

  • Behavior: Process execution alternates between bursts of CPU usage and waiting for I/O, categorized into CPU-bound and I/O-bound processes.

Process Management

  • Process Table: Managed by the OS, containing entries for each process, including state, resources used, and identifier information.

  • Operations: Include creating, terminating, and scheduling processes, among others.

  • Creating Processes: Uses fork to create a duplicate of a process and execv to run a new program.

Threads

  • Definition: Threads, or Light-weight processes (LWP), represent multiple execution paths within the same process, sharing the same memory space.

Conclusion

  • This lecture comprises key components of system architecture, bootstrapping, system calls, CPU utilization, and process management. Understanding these foundational elements is essential for comprehending how operating systems manage hardware and software resources effectively.

Computer System Architecture focuses on various processor configurations and system management processes.

Single-Processor Systems

  • A system with a general-purpose processor executing one instruction at a time.

Multiprocessor Systems

  • Two or more processors working together, sharing the same RAM and executing multiple programs simultaneously.

Multicore Systems

  • A type of multiprocessor system with multiple cores on a single chip, enabling efficient on-chip communication.

Clustered Systems

  • Comprising multiple nodes working together, can consist of single or multicore systems.

Bootstrapping

  • The initialization process loading the operating system (OS) kernel into RAM, using a boot loader for hardware checks.

BIOS/UEFI

  • Loads the Master Boot Record (MBR) into RAM, with UEFI supporting larger disks and faster booting.

System Calls

  • An interface for user programs to request OS services, operating in User Mode and Kernel Mode.

CPU Utilization

  • Calculated as Utilization = Time Used / (Time Used + Time Wasted). Utilization can be predicted based on the number of programs waiting for I/O.

Processes

  • Dynamic execution of a program, with states like Running, Ready, and Blocked, balancing CPU usage and I/O waiting.

Threads

  • Light-weight processes allowing multiple execution paths within the same process, sharing memory.

Conclusion

  • Key components include system architecture, bootstrapping, system calls, CPU utilization, and process management, vital for understanding OS functions.