UNIX System Administration OS Kernal Copyright 2002, Dr. Ken Hoganson All rights reserved. OS Kernel Concept Kernel or MicroKernel Concept: An OS architecture-design concept/philosophy Identify and create a minimal set of OS functions that are hardware/platform dependent: –Interface with the hardware –For speed: continuously needed OS functions that are always running and available –The kernel must be modified for different HW platforms The remaining OS functions and facilities are grouped as service or sub- system packages –Interface though the kernel –Hardware platform INDEPENDENT –Consist programming interface on different hardware platforms Pg 100+ Goldman

UNIX System Administration OS Kernal Copyright 2002, Dr. Ken Hoganson All rights reserved. Kernel Functions CPU Time management/Process Management: –Scheduler/dispatcher/context-switch code –Overhead – needs to be very fast –Register set dependent Memory Management –Virtual Memory –Allocating and Freeing memory programming interface Interrupt and Exception Handling: –Hardware dependent – bus, interrupt structure –Must be very fast Inter-process Communication –Processes/threads communicate on same machine through message passing –Communicate to other machines through a network interface Interface to hardware-specific Device Drivers

UNIX System Administration OS Kernal Copyright 2002, Dr. Ken Hoganson All rights reserved. Kernel OS Structure CPU Memory I/O Bus Time & Process Mem & V.M. Device Drivers Kernel Sub- Systems Users & Security File System Disk & Storage App. Mngt. Command Line GUI Account Config & Pref Application Layer(s) User Interface

UNIX System Administration OS Kernal Copyright 2002, Dr. Ken Hoganson All rights reserved. This layered kernel OS architecture promotes: Portability: only the kernel needs to be modified for each HW system Software Engineering: compartmentalizes complexity, resulting in more modifiable and reliable code, with less effort Multiple OS “Personalities”: the user interface module can be customized, configured, and replaced Different vendors can create/package an OS built around a standard OS kernel: LINUX flavors and vendors Promotes standardization Promotes interoperability Pg Goldman

UNIX System Administration OS Kernal Copyright 2002, Dr. Ken Hoganson All rights reserved. PROCESS OR TASK: A program that is loaded in the computer’s memory and is available for execution. A process has a unique address space and resources. Processes are managed by the OS. THREAD: A separate “thread of execution”, or subset of a PROCESS that can execute independently in conjunction with other threads. Threads share address space and resources. Threads are often managed through code in a language library, in this case, the thread is “invisible” to the OS, which sees only the parent PROCESS PORT: A communication interface (software function) that allows processes to communicate using message-passing. Processes on the same host or different hosts can communicate through ports.

UNIX System Administration OS Kernal Copyright 2002, Dr. Ken Hoganson All rights reserved. Communication Strategies: Message Passing –Requires a message frame/structure, addressing, packet management –Transferred using “store-and-forward” or “worm-hole-routing” –Overhead processing & time delay Shared Memory; –Requires semaphores/concurrency management to coordinate contention and shared access –Less overhead, no frames. –Harder to do on separate hosts

UNIX System Administration OS Kernal Copyright 2002, Dr. Ken Hoganson All rights reserved. Multi-processor: more than one processor available –Different processes on different processors –Same process on different processors, perhaps divided into threads for parallel processing Symmetric Multi-processing: multiple identical processors Multi-threaded: supports multiple threads per process Virtual Machine: another OS software layer inserted below the kernel –Supports HW level ‘aliasing’ –Supports multiple copies of OS running –Great for upgrades, testing, development Analysis and comparison of operating systems: Pg 108 – go over in class