Operating System Fundamentals

Course Outline and Introductory Considerations

• The initial focus is on understanding fundamental considerations in operating systems.
• Subsequent weeks will delve into common strategies that address these considerations.

Thought Experiment: Running Programs on Bare Metal

• Key components for directing a program to run on bare metal include the program itself, tasking, memory managment, and interacting with devices.
• Running two programs would necessitate changes in how resources and tasks are managed.

Components of a Modern Computer

• Modern computers contain at least one processor, main memory, disks, printers, keyboard, mouse, display, network interfaces, and I/O devices.
• The operating system mediates between user-mode software and the hardware in kernel mode.

The Operating System as Abstraction

• Operating systems transform raw hardware into user-friendly abstractions.

The Operating System as Resource Manager

• The top-down view of an OS provides abstractions to application programs.
• The bottom-up view is that the OS manages pieces of a complex system.
• Another perspective is that the OS provides controlled allocation of resources.

History of Operating Systems by Generation

• First generation (1945–55): vacuum tubes
• Second generation (1955–65): transistors and batch systems
• Third generation (1965–1980): ICs and multiprogramming
• Fourth generation (1980–present): personal computers
• Fifth generation (1990–present): mobile computers

Transistors and Batch Systems

• Batch systems involve programmers submitting jobs on cards to a machine like the 1401.
• I/O from tape is done on the 7094 system.
• A typical FMS job structure includes $JOB card identifying the user, FORTRAN program, data, and a $END card.

ICs and Multiprogramming

• Multiprogramming systems keep multiple jobs in memory simultaneously.

Modern Processors

• Modern computers include components such as CPU, MMU, memory, video controller, keyboard controller, USB controller, and disk controller.

Processors

• Modern CPUs use pipelines and superscalar architectures for faster execution.
• A three-stage pipeline involves fetch, decode, and execute.

Memory Hierarchy

• Memory systems use caching to improve access times
• A quad-core chip can have a shared L2 cache or separate L2 caches for each core
• Memory hierarchy consists of registers (<1KB, 1 nsec), cache (4MB, 2 nsec), main memory (1-8GB, 10 nsec), and magnetic disk (1-4TB, 10 msec)

Memory Caching System Issues

• Key considerations include when to cache a new item, where to place it in the cache line, which item to evict, and where to place evicted items in larger memory.

Structure of Disks

• A disk drive includes multiple surfaces with read/write heads.

I/O Devices and Interrupts

• Using an I/O device involves the CPU triggering the interrupt controller and disk controller.
• Interrupt processing encompasses capturing the interrupt, activating the interrupt handler, and resuming the user program.

Buses

• A modern x86 system includes components such as cores, memory controllers, and peripherals connected through various buses.

Operating System Zoo

• This includes mainframe, server, multiprocessor, personal computer, handheld, embedded, sensor node, real-time, and smart card operating systems.

Processes

• Processes are a key concept, defining a program in execution.
• Processes have an associated address space and set of resources.
• A process can be considered a container holding all information needed to run a program.
• Processes form a process tree where parent processes create child processes.

Files and File Systems

• File systems are typically organized in a hierarchical directory structure.
• Mounting a file system makes files on a device like a CD-ROM accessible within the file hierarchy.
• Processes can communicate through pipes.

Ontogeny Recapitulates Phylogeny

• This principle means new computer "species" evolve similarly to their ancestors, bringing back old concepts due to technological changes.

System Calls

• System calls involve a sequence of steps, including trapping to the kernel and invoking the system call handler.

POSIX System Calls

• Some major POSIX system calls include process management, file management, and directory/file system management.
  • Process management includes fork(), waitpid(), execve(), and exit().
  • File management includes open(), close(), read(), write(), lseek(), and stat().
  • Directory and file system management includes mkdir(), rmdir(), link(), unlink(), mount(), and umount().
  • Miscellaneous calls include chdir(), chmod(), kill(), and time().
• The return code s is usually -1 if an error occurred.
  • In the return codes pid is a process id.
  • fd is a file descriptor.
  • n is a byte count.
  • position is an offset within the file.
  • seconds is the elapsed time
• A stripped-down shell uses system calls to repeat a command or wait for a child process to exit.

Memory Segments in Processes

• Processes possess three segments: text, data, and stack.

Directory Management

• Directory management links or mounts directories/devices.

Windows Win32 API

• The Win32 API offers analogous calls to UNIX functions for process, file, and directory management. Win32 API may not support some functions.

Monolithic Systems

• A monolithic OS contains a main program, service procedures, and utility procedures.

Layered Systems

• The THE operating system consists of several layers: operator, user programs, I/O management, operator-process communication, memory/drum management, and processor allocation/multiprogramming.

Microkernels

• Microkernels handle interrupts, processes, scheduling, and IPC.
• Servers and drivers run in user mode.

Client-Server Model

• The client-server model operates over a network with machines serving different functions like file, process, and terminal services.

Virtual Machines

• Virtual machines include CMS (Conversational Monitor System) and trap to handle system calls.
• VM/370 is a known virtual machine.

More Recent Virtual Machines

• Type 1 hypervisors run directly on hardware, while type 2 hypervisors run on top of a host OS.

Large Programming Projects

• Compiling C code involves steps such as preprocessing, compiling, linking, and creating an executable binary.

Metric Units

• Metric prefixes range from yocto (10^-24) to yotta (10^24.)