Operating system 15 micro kernel based os

Operating system 15 micro kernel based os

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  Operating System 15 MicroKernel Based OS Prof Neeraj Bhargava Vaibhav Khanna Department of Computer Science School of Engineering and Systems Sciences Maharshi Dayanand Saraswati University Ajmer
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  Kernel based OS •Everything below the system-call interface and above the physical hardware is the kernel. • The kernel provides the file system, CPU scheduling, memory management, and other operating system functions through system calls. • Taken in sum, that is an enormous amount of functionality to be combined into one level. • Systems programs use the kernel-supported system calls to provide useful functions, such as compilation and file manipulation.
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  Kernel based OS •System calls define the programmer interface to UNIX; the set of systems programs commonly available defines the user interface. • The programmer and user interfaces define the context that the kernel must support. • Several versions of UNIX have been developed in which the kernel is partitioned further along functional boundaries. • The AIX operating system, IBM's version of kernel based OS separates the kernel into two parts. • Mach, from Carnegie Mellon University, reduces the kernel to a small set of core functions by moving all nonessentials into systems and even into user-level programs. • What remains is a microkernel operating system implementing only a small set of necessary primitives.
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  Microkernel System Structure •Moves as much from the kernel into user space • Mach example of microkernel – Mac OS X kernel (Darwin) partly based on Mach • Communication takes place between user modules using message passing • Benefits: – Easier to extend a microkernel – Easier to port the operating system to new architectures – More reliable (less code is running in kernel mode) – More secure • Detriments: – Performance overhead of user space to kernel space communication
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  Microkernel System Structure Application Program File System Device Driver Interprocess Communication memory managment CPU scheduling messages messages microkernel hardware user mode kernel mode
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  Modules • Many modernoperating systems implement loadable kernel modules – Uses object-oriented approach – Each core component is separate – Each talks to the others over known interfaces – Each is loadable as needed within the kernel • Overall, similar to layers but with more flexible – Linux, Solaris, etc
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  Solaris Modular Approach
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  Extensible Nucleus, orMicrokernel, Organization • The extensible nucleus organization is a modular organization intended to implement real-time systems, timesharing systems, and the like, by using a common set of skeletal facilities. • The approach is to define two types of modules for any particular OS: policy-specific modules and the skeletal policy-independent modules. • The policy-independent modules implement the extensible nucleus, or microkernel. • It is not intended to provide complete functionality. Rather, it is supposed to create an environment in which policy-specific operating systems can be constructed to meet the needs of an application domain. • The skeletal component is a general-purpose foundation for policy- specific parts of the architecture.
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  Philosophy of Policybased OS • The philosophy behind this approach is that the OS can be implemented in two parts: • (1) a mechanism-dependent, hardware-dependent part • (2) a policy-dependent, hardware-independent part. • The first part provides a low-level virtual machine with some form of memory and process management, usually with only the bare essentials for device management. • The second part reflects the requirements of the specific OS. This architecture supports two new directions in operating systems. • It allows policy-dependent variants of an OS to be built on a single hardware platform. • The microkernel provides skeletal, policy-independent functions that are extended with specialized servers to implement a policy.
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  Microkernel • A microkernel(also known as μ-kernel) is the near-minimum amount ofsoftware that can provide the mechanisms needed to implement an operating system (OS). • These mechanisms include low-level address space management, thread management, and inter-process communication (IPC). • Early operating system kernels were rather small, partly because computer memory was limited. • As the capability of computers grew, the number of devices the kernel had to control also grew.
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  Era of BigKernels • The Berkeley Software Distribution (BSD) of Unix began the era of big kernels. • In addition to operating a basic system consisting of the CPU, disks and printers, BSD started adding additional file systems, a complete TCP/IP networking system, and a number of "virtual" devices that allowed the existing programs to work invisibly over the network. • This growth continued for many years, resulting in kernels with millions of lines of source code. • As a result of this growth, kernels were more prone to bugs and became increasingly difficult to maintain.
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  Monolithic to Microkernels
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  Birth of MicroKernels • The microkernel was designed to address the increasing growth of kernels and the difficulties that came with them. • In theory, the microkernel design allows for easier management of code due to its division into user space services. • This also allows for increased security and stability resulting from the reduced amount of code running in kernel mode
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  Microkernels and IPC •Inter-process communication (IPC) is any mechanism which allows separate processes to communicate with each other, usually by sending messages. • Shared memory is strictly speaking also an inter-process communication mechanism, but the abbreviation IPC usually only refers to message passing, and it is the latter that is particularly relevant to microkernels. • IPC allows the operating system to be built from a number of small programs called servers, which are used by other programs on the system, invoked via IPC. • Most or all support for peripheral hardware is handled in this fashion, with servers for device drivers, network protocol stacks, file systems, graphics, etc.
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  Server Based Approachin Microkernel • A basic set of servers for a general-purpose microkernel includes file system servers, device driver servers, networking servers, display servers, and user interface device servers. • This set of servers (drawn from QNX) provides roughly the set of services offered by a Unix monolithic kernel. • The necessary servers are started at system startup and provide services, such as file, network, and device access, to ordinary application programs. • Many "crashes" can be corrected by simply stopping and restarting the server
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  Assignment • Explain theneed and concept of MicroKernels.