ENVS 1500 Lecture Notes - Lecture 11: Monolithic Kernel, Protected Mode, Device Driver
13 May 2018
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ENVS 1500 Tutorial 11 Notes – Monolithic Kernel
Introduction
• In this model, the various memory resident operating system functions are represented
by a monolithic kernel.
• There is no specific organization.
• The operating system programs simply interact as required to perform their functions.
• The critical functions within the kernel operate in protected mode, the remainder, in
user mode.
• The shell is separate from the kernel and serves as an interface between the users,
utilities, and user programs with the kernel.
• Thus, the shell can be replaced without affecting kernel operations.
• UNIX organization is considered in more detail as a case study in Supplementary
• The major difficulty with a monolithic configuration is the stability and integrity of the
system as a whole.
• Any defect in a program within the kernel can crash the entire system, as can
unexpected interactions between different programs in the kernel.
• Thus, the addition of a new device driver, for example, could compromise the entire
system.
• Nonetheless, with proper design and control, it is possible to build a secure and stable
system, as evidenced by Linux.
• An alternative operating system organization is built around a hierarchical structure.
• A simple representation of a hierarchical operating system organization is shown
• This representation shows the operating system divided into layers.
• The upper layers are the ones that are visible to the user.
• The middle layers comprise the major kernel operations.
• The lowest layers are the I/O device drivers that interact with the hardware.
• In this model, each layer is relatively independent of the other layers.
• Operating system programs simply interact as required to perform their functions.
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