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Interrupts, MultiTasking, MultiProgramming, System Programs , 6 Jan 2021
59:09

Interrupts, MultiTasking, MultiProgramming, System Programs , 6 Jan 2021

Abhi

6 chapters8 takeaways16 key terms7 questions

Overview

This video explains the fundamental concepts of how a computer boots up, including the roles of BIOS and bootloaders, and delves into the distinction between kernel and application programs. It clarifies how operating systems manage hardware through interrupts, emphasizing the hardware's role in initiating these processes and the OS's subsequent control. The discussion also touches upon multiprocessor systems and symmetric multiprocessing architectures, highlighting the shared memory model. Finally, it addresses common misconceptions about hardware interrupts, explaining their signal-based nature and the OS's responsibility in handling them.

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Chapters

  • The boot process starts with the BIOS, which initializes hardware and then loads the bootloader.
  • The bootloader (e.g., GRUB) resides in sector zero of a bootable device and is responsible for loading the operating system.
  • A bootable device is defined by the presence of bootloader code in its boot sector.
  • The BIOS allows the user to select the boot device, but it's the bootloader that ultimately loads the OS.
Understanding the boot process is crucial for comprehending how a computer starts and how the operating system gains control.
When a computer starts and displays 'Press F9 for boot options,' this is the BIOS allowing the user to choose a boot device like a USB drive or hard disk.
  • The CPU's fundamental operation throughout its lifetime is a continuous cycle of fetch, decode, execute, and program counter update.
  • Installing an OS involves copying its code from an installation medium to the target persistent storage device.
  • The OS code resides in RAM during execution, not directly within the CPU.
  • The CPU transfers data to and from memory and devices; DMA allows devices to transfer data to RAM without direct CPU intervention.
This clarifies the core function of the CPU and the practical meaning of OS installation, distinguishing between persistent storage and active memory.
The installation of an OS means copying files from a DVD or USB drive onto the computer's hard drive.
  • The kernel is the core of the OS, managing hardware, while applications are programs that utilize OS functionalities.
  • System programs are special applications that depend on the kernel but are still considered applications.
  • A schematic diagram shows applications running on top of the OS, which in turn uses hardware features.
  • Applications can directly access the CPU, bypassing the OS for execution, though the OS manages resource allocation.
Differentiating between the kernel and applications helps understand the layered structure of software and how programs interact with hardware.
When you use a text editor or a web browser, you are interacting with an application program, which then communicates with the operating system's kernel.
  • Modern computers are often multiprocessor systems, featuring multiple CPU cores on a single chip (dual-core, quad-core) or multiple separate processor chips.
  • Symmetric Multiprocessing (SMP) is an architecture where multiple CPUs share a single memory bank, providing equal access to all processors.
  • Each CPU core has its own registers and cache, but they access a common main memory.
  • From an OS programmer's perspective, dual-core or quad-core processors are logically treated as multiple independent processors.
Understanding multiprocessor systems is essential as most modern computers utilize them, impacting how operating systems manage tasks and resources.
A dual-core processor has two complete processing units (cores) embedded within a single physical chip, allowing them to execute tasks concurrently.
  • A hardware interrupt is an electrical signal sent to the CPU by a hardware device, indicating a need for attention.
  • When an interrupt occurs, the CPU's normal execution flow is halted, and the program counter is redirected to a predetermined address in memory (Interrupt Vector Table - IVT).
  • The OS pre-populates these interrupt addresses with its own code to handle the specific hardware event.
  • The hardware itself manages interrupt priorities; the OS programmer's role is to provide the code at the designated interrupt locations.
This explains how hardware devices signal the CPU and how the operating system takes control to manage these events, enabling responsiveness.
When you press a key on your keyboard, the keyboard controller sends an electrical signal to the CPU, triggering a hardware interrupt that causes the OS to run code to process the keystroke.
  • Hardware devices (like keyboards, mice, hard disks) are 'dumb' and perform specific, independent functions; they do not inherently understand programs or OS tasks.
  • The OS programmer's role is to integrate these hardware components and their signals into a cohesive system, making the 'magic' happen.
  • BIOS code, stored in ROM, is manufacturer-specific and initializes hardware; it's distinct from bootloaders on hard disks.
  • Interrupts are handled by hardware, which directs the CPU to specific OS code locations, allowing the OS to manage the hardware event.
This section emphasizes that hardware is not intelligent on its own and that the OS programmer's design is what creates the functionality users experience.
A mouse generates electrical signals when moved or clicked, but it's the OS that interprets these signals to move the cursor or perform an action within an application.

Key takeaways

  1. 1The boot process is a sequential chain: BIOS -> Bootloader -> OS.
  2. 2Operating system installation is fundamentally about copying OS files to persistent storage.
  3. 3The CPU continuously executes instructions; programs must be loaded into RAM to be executed.
  4. 4The kernel is the core OS component that directly manages hardware, while applications provide user functionality.
  5. 5Modern computers commonly use multiprocessor architectures, with Symmetric Multiprocessing (SMP) being a prevalent model where CPUs share memory.
  6. 6Hardware interrupts are electrical signals initiated by hardware that cause the CPU to pause its current task and execute OS-defined interrupt handler code.
  7. 7The OS gains control over hardware by providing specific code at memory locations that the CPU jumps to upon receiving a hardware interrupt.
  8. 8Hardware components perform specific, limited functions; it is the OS and system design that create complex computer system behavior.

Key terms

BIOSBootloaderBootable DeviceSector ZeroCPU Fetch-Decode-Execute CycleKernelApplication ProgramSystem ProgramMultiprocessor SystemSymmetric Multiprocessing (SMP)Hardware InterruptInterrupt Vector Table (IVT)Program Counter (PC)Direct Memory Access (DMA)ROMHard Disk

Test your understanding

  1. 1What is the primary role of the BIOS during the computer's boot process, and how does it differ from the bootloader's function?
  2. 2Explain the fundamental cycle of operations performed by the CPU throughout its lifetime.
  3. 3How does the installation of an operating system differ from loading an OS into RAM for execution?
  4. 4What is the key distinction between a kernel and an application program, and how do they interact with hardware?
  5. 5Describe the concept of Symmetric Multiprocessing (SMP) and how multiple processors access memory in this architecture.
  6. 6What is a hardware interrupt, and how does the CPU respond to one?
  7. 7How does the operating system leverage hardware interrupts to gain control over hardware devices?

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