Mach is one of the most influential examples of a microkernel-based operating system. It was developed at Carnegie Mellon University (CMU) from 1985 to 1994, and it served as the foundation for several real systems, such as NextOS (which later evolved into Mac OS X), OSF/1,
and GNU Hurd. Mach introduced many innovative features to the operating system design, such as virtual memory management, interprocess communication (IPC), threads, scheduling, and multiprocessor support.
Virtual Memory Management
Mach provides a flexible and powerful mechanism for managing virtual memory. The Mach kernel implements only the low-level functions for allocating physical memory pages and mapping them to virtual addresses. The higher-level functions,
such as paging, swapping, caching, and protection, are delegated to user-level memory managers. The memory managers can implement different policies and algorithms for managing different types of memory objects, such as files, anonymous memory, shared memory, and device memory. The memory managers communicate with the kernel through a set of IPC messages that allow them to request and manipulate memory regions, called memory objects.
Interprocess Communication
Mach provides a fast and efficient mechanism for interprocess communication. The Mach kernel implements only the low-level functions for sending and receiving messages between processes. The higher-level functions,
such as naming, authentication, synchronization, and serialization, are delegated to user-level port managers. The port managers can implement different protocols and semantics for communicating with different types of ports, such as sockets, pipes, RPCs, and shared memory. The port managers communicate with the kernel through a set of IPC messages that allow them to create and manipulate ports.
Threads
Mach provides a flexible and powerful mechanism for managing threads. The Mach kernel implements only the low-level functions for creating and destroying threads, switching contexts, and handling exceptions. The higher-level functions,
such as scheduling, synchronization, priority inheritance, and cancellation, are delegated to user-level thread managers. The thread managers can implement different policies and algorithms for managing different types of threads, such as real-time threads, preemptive threads, cooperative threads, and kernel threads. The thread managers communicate with the kernel through a set of IPC messages that allow them to create and manipulate thread ports.
Scheduling
Mach provides a flexible and powerful mechanism for scheduling processes and threads. The Mach kernel implements only the low-level functions for selecting the next runnable thread on each processor and dispatching it to execution. The higher-level functions,
such as queue management, load balancing, affinity scheduling, and feedback control, are delegated to user-level scheduler managers. The scheduler managers can implement different policies and algorithms for scheduling different types of processes and threads, such as fair-share scheduling, round-robin scheduling,
lottery scheduling,
and earliest deadline first scheduling.
The scheduler managers communicate with the kernel through a set of IPC messages that allow them to create and manipulate scheduler ports.
Multiprocessor Support
Mach provides a flexible and powerful mechanism for supporting multiprocessor systems. The Mach kernel implements only the low-level functions for initializing and synchronizing processors, handling interrupts,
and maintaining cache coherence.
The higher-level functions,
such as processor allocation,
processor migration,
processor affinity,
and processor power management,
are delegated to user-level processor managers.
The processor managers can implement different policies and algorithms for managing different types of processors,
such as symmetric multiprocessing (SMP),
asymmetric multiprocessing (AMP),
and heterogeneous multiprocessing (HMP).
The processor managers communicate with the kernel through a set of IPC messages that allow them to create and manipulate processor ports.
Conclusion
Mach is a microkernel-based operating system that provides only the basic mechanisms for managing hardware resources, and delegates the rest of the operating system functions to user-level servers.
Mach demonstrates that the microkernel architecture can achieve high levels of functionality
and performance
without sacrificing modularity
and flexibility.
Mach has influenced the design and implementation of many other operating systems,
such as Mac OS X,
OSF/1,
and GNU Hurd.
References
[1]: Microkernel Operating System Architecture and Mach, David L. Black et al., 1991.
[2]: Microkernel-based Operating Systems - Introduction, Carsten Weinhold, 2017.
[3]: System Architecture, 2003.
[4]: MIcrokernel PDF, 2014.
[5]: Introduction to Microkernel- Based Operating Systems, Hermann HÃrtig, 2010.
a104e7fe7e