Operating System History and Computer Architecture

Operating System History

• First-generation computers (1945-1955) used relays and vacuum tubes, relying on plugboards for input and printers for output.
• Second-generation computers (1955-1965) transitioned to transistors, with punch cards and printers for I/O.
• Third-generation computers (1965-1980) featured integrated circuits (ICs), adopted punch cards and tape drives for input and output.
• Fourth-generation computers (1980-present) encompassed personal computers, utilizing large-scale integration (LSI), floppy disks, CD-ROMs, USB, and networks for input, and printers, monitors, and displays for output.

Computer Architecture

• A computer is a digital electronic machine that can be programmed to automatically execute sequences of arithmetic and logical operations.
• Instructions given to the computer to execute operations are called programs.
• Programs encompass tasks like creating files, retrieving system time, reading from USB devices, and transferring data over networks.
• System calls are functions that interact with the operating system's kernel.
• Device drivers are specialized programs that allow the operating system to communicate with hardware components.

Protection Rings

• Protection rings are hierarchical layers in the CPU architecture that implement restrictions on the set of instructions allowed to execute.
• These rings help ensure safe execution by isolating core system functions from user-level processes.
• x86 CPUs (Intel, AMD) support four rings (0-3), but most operating systems only implement two: ring 0 (kernel mode) and ring 3 (user mode).

Kernel Mode and User Mode

• Kernel mode is the most privileged operating mode, allowing direct access to all system resources including memory and hardware.
• Programs running in Kernel Mode can potentially crash the system, leading to an irrecoverable halt.
• User mode is a less privileged mode, limiting code execution's access to system resources (hardware and primary memory).
• Most executed code runs in user mode, using a subset of available CPU instructions.
• User mode programs depend on system calls to interact with hardware components.

Kernel Space and User Space

• Kernel space is the memory region where the operating system operates.
• User space is the memory region used for user programs.
• It's important to distinguish between kernel mode/space and user mode/space as they refer to different aspects of program execution and memory allocation.

System Calls

• System calls are functions that allow user-level processes to access kernel services and hardware resources.
• When a user process needs to perform an action requiring privileged access, it makes a system call.
• The system call is trapped by the operating system kernel, which interprets its code and executes the corresponding service.

Virtualization

• Virtualization is the process of creating a software-based simulation of something, such as virtual computer hardware, networks, or operating systems.
• A virtual machine (VM) represents a software-based simulation of a computer.
• A hypervisor is the software that manages and executes virtual machines.
• The computer running the hypervisor is known as the host machine, and the virtualized computer is referred to as the guest machine.

Hypervisor Types

• Type-1 hypervisors (bare-metal hypervisors) run directly on the hardware, providing a platform for virtual machines to operate on top of it.
• Type-2 hypervisors (hosted hypervisors) run within a host operating system, leveraging the host system's kernel to access hardware resources.

Speed Comparison

• Referencing registers is the fastest operation, taking 1 nanosecond (10-9 seconds).
• Accessing main memory requires slightly more time, taking 10 nanoseconds (10-8 seconds).
• System calls take 1 microsecond (10-6 seconds) for execution.
• Context switching requires 10 microseconds (10-5 seconds).
• Reading 1 bit from a solid-state drive (SSD) takes 100 microseconds (10-4 seconds), while reading from a hard disk drive (HDD) takes 10 milliseconds (10-2 seconds).
• Transferring 1 megabyte (MB) over the network takes 1 second (100 seconds).

Explore the evolution of operating systems and computer architecture through the generations. This quiz covers the key advancements from first-generation computers to the fourth generation, along with the fundamentals of how computers execute programs. Test your knowledge of the technological progression and functional components of modern computing.