ENVS 1500 Lecture Notes - Lecture 12: Microkernel, Device Driver
13 May 2018
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ENVS 1500 Tutorial 12 Notes – Hardware Directly
Introduction
• The file management layer determines the location of file identified by logical name and
interprets the nature of the request, but does not attempt to access the hardware
directly.
• Instead, it makes a request to the kernel. Local requests are then passed on to the I/O
device driver level for access to the hardware.
• Network requests are passed on to the I/O device drivers on the machines providing the
services.
• The hierarchy is arranged so that access to the various layers of the operating system is
from the top.
• Each layer calls the next lower layer to request the services that it needs.
• Most computer systems today provide appropriate hardware instructions that allow the
operating system design to enforce this procedure.
• This provides security, as well as a clean interface between the different functions
within the operating system.
• Layered operating systems must be designed carefully, because the hierarchy requires
that services be layered in such a way that all requests move downward.
• A program at a particular layer must never require services from a higher layer because
this could compromise system integrity.
• Another disadvantage of the layered approach is the time required to pass the request
through intermediate layers to receive services from the lowest layers.
• In contrast, a program in a monolithic operating system could request the service
directly from the program that supplies the service, resulting in much faster operation.
• The obvious advantage of the layered approach is the stability and integrity that result
from a well-structured modular design.
• Still another approach to operating system design is the microkernel.
• An illustration of a microkernel configuration is shown
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