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Architecture
specific
OS Designs
Class Notes
Operating System Designs
Operating system serves as a platform to run all kinds of applications. Basically OS is integration of two
modules.
a) User Interfaceb) Kernel
Generic Kernel
System calls
Hardware /Peripherals
Kernel
Loader
Process
management
Access
Control
IPCMemory
Management
Network
ServicesIO File
system
Device
Drivers
Hardware /Peripherals
System calls
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Kernel is a collection of various subsystems that provides services to an application.
Loader, Kernel and Architecture specific together called as Core Subsystem. They are responsible forsystem initialization and resource management.
Remaining all are called service subsystems.
Architecture specific (HAL / BSP): This layer is responsible for platform initialization which includes processor
and I/O controllers.
In-Kernel: This layer is responsible for data initialization and initializing other kernel subsystems.
Loader: This layer is responsible for loading an application by allocating required memory.
Service Subsystems:
These subsystems are responsible for providing resources for the applications at the runtime.
TYPES OF OPERATING SYSTEMS
1) General purpose OS:This type of OS is designed for desktop computers. It provides lots of services and supports any
applications. Here the Kernel will be very heavy.
2)
Embedded OS:This type of OS is designed for closed devices usually targeted for RISC (Reduced Instruction Set
computing) architecture, and services are fine tuned for specific set of applications. The kernel will be
light.
3) Real Time OS:This OS has fixed time response.
Operating System Design:
In earlier days, user applications and Kernel were aligned together. There by any bug in that application
crashed the entire OS.
To ensure that exceptions caused by an application do not result in kernel crash, memory (RAM) is logically
partitioned into kernel space and User space. Applications are loaded in user space and Kernel is loaded in
kernel space.
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Monolithic Kernel:
Most of the Desktop OS are monolithic. The applications are completely abstracted from kernel. The main drawback of Monolithic kernel is the buggy drivers installed from un-trusted sources can
crash the kernel.
Micro Kernel:
U-space
Middle ware
K-space
Application A Application CApplication B
Stacks (TCP/IP, USB, )
Driver
Kernel Interrupt Handler
Hardware Peripherals
Application A Application CApplication B
Driver A Stack(TCP/IP) Stack File system
Kernel Driver B Interrupt
Handler
Hardware Peripherals
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Here the third party services are put on the middle layer. Example: Android.
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