David R. Cheriton, M. A. Malcolm, L. S. Melen, and G. R. Sager. Thoth, A Portable Real-Time Operating System. Communications of the ACM, 22(2):105--115, February 1979.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....performance under different circumstances. Thus it is important to provide operating system facilities that are appropriate to the application. Micro kernels have addressed this problem by providing a minimal kernel, and encapsulating the rest of OS functionality in replaceable server processes [4, 5, 9, 10, 15, 22, 27]. Such systems can be customized by replacing or providing additional servers that implement the desired policies while making use of existing mechanisms provided by the micro kernel. Using this approach, customization is supported at a coarse granularity, through the replacement of complete ....

David R. Cheriton, M. A. Malcolm, L. S. Melen, and G. R. Sager. Thoth, A Portable Real-Time Operating System. Communications of the ACM, 22(2):105--115, February 1979.

....and has lead us to focus our attention on providing light weight process groups. The architecture of HORUS was influenced by microkernel design concepts, in which several light weight mechanisms are provided in user space. The most obvious of these is the light weight process or thread abstraction[8, 15]. Another well known, older abstraction is memory allocation. These abstractions not only allow easier resource management by sharing most of a core environment, but also provide a portable interface across different environments. The basic idea behind the light weight process group (LWG) ....

D. R. Cheriton and W. Z. Zwaenepoel. Thoth, a portable real-time operating system. Communications of the Association for Computing Machinery, pages 105 -- 115, February 1979.

....When a process in one address space requests a service from another address space, it creates a message describing its requirements, and sends it to the target address space. A process in the target address space receives the message, interprets it and services the request. THE [72] Thoth [56], and Demos [16] are a few examples of the earliest message passing systems. The primary motivation behind the design of these systems was to decentralize the structure of an operating system running on a single computer. On the other hand, the motivation behind the latter message passing systems ....

D.R. Cheriton, M.A. Malcolm, L.S. Melen, and G.R. Sager. Thoth, a portable real-time operating system. Comm. of the Assoc. Comput. Mach., 22(2):105--115, Feb. 1979.

....performance under different circumstances. Thus it is important to provide operating system facilities that are appropriate to the application. Micro kernels have addressed this problem by providing a minimal kernel, and encapsulating the rest of OS functionality in replaceable server processes [5, 6, 10, 11, 17, 24, 29]. Such systems can be customized by replacing or providing additional servers that implement the desired policies while making use of existing mechanisms provided by the micro kernel. Using this approach, customization is supported at a coarse granularity, through the replacement of complete ....

David R. Cheriton, M. A. Malcolm, L. S. Melen, and G. R. Sager. Thoth, A Portable Real-Time Operating System. Communications of the ACM, 22(2):105--115, February 1979.

....for both copying and checkpointing. In 1979, most related work was yet to start (or not yet widely known) Accent [Ras 81] and its successor Mach [Acc 86] used copy on write techniques. These and various other systems (e.g. Amoeba [Mul 84] Chorus [Gui 82] V [Che 84] and its predecessor Toth [Che 79] are based on the message passing paradigm, but not on the persistence paradigm. The programming languages Elle [Alb 80] and PSAlgol [Atk 82] already handled persistent and transient data uniformly. To date, partial data persistence (without dealing with faults) is part of the the Comandos [Cah ....

D. Cheriton, D. A. Malcolm, L. S. Melen, G. R. Sager. Thoth, a Portable Real-Time Operating System. CACM 22(2), February 1979, pp. 105-115.

....this hardware core as the basis for their implementation. A Sylvan task has its own context and thread of execution. When a task is created, it is assigned a unique Task IDentifier (TID) and a protected virtual address space. Tasks communicate among themselves by way of synchronous message passing[9]. Groups of tasks are used to provide operating system services using a technique known as multiprocess structuring. Sylvan tasks are intended to be used as a unit of abstraction, hence the emphasis on low latency tasking operations. Tasks are a concurrent abstraction; there are no concurrency ....

....independent of the proximity of the tasks. No special capabilities are granted to physically nearby tasks; all such optimizations are embodied within the tasking kernel. The concepts of synchronous message passing and multiprocess structuring were first developed in the Thoth operating system [9], and have proven their value in numerous projects and systems [2, 10, 15, 21, 30, 17, 33] These projects demonstrate that operating systems may be developed in a natural fashion using a simple tasking kernel as a basis. Synchronous message passing and multiprocess structuring have also been ....

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David R. Cheriton, M. A. Malcolm, L. S. Melen, and G. R. Sager. Thoth, A Portable Real-Time Operating System. Communications of the ACM, 22(2):105--115, February 1979.

....choices unnecessarily, are the key to gaining the most benefit from techniques such as specialization. 6 Related Work Our work on optimistic incremental specialization can be viewed as part of a widespread research trend towards adaptive operating systems. Micro kernel operating systems [5, 6, 11, 9, 21, 27, 29] were an early example of this trend, and improve adaptiveness by allowing operating system functionality to be implemented in user level servers that can be customized and configured to produce specialpurpose operating systems. While micro kernel based architectures improve adaptiveness over ....

David R. Cheriton, M. A. Malcolm, L. S. Melen, and G. R. Sager. Thoth, A Portable Real-Time Operating System. Communications of the ACM, 22(2):105--115, February 1979.

....switching overhead [Bak90] YARTOS has been used to support a digital conferencing application [JSS92] a HiPPI data link controller and a virtual reality system. 4.2. 5 Real time Threads: Toward Portable Real time Kernels Portability is an important attribute of real time operating systems[CMMS79] because their target hardware routinely varies from special purpose processors, to parallel machines, to distributed execution environments. Unfortunately, portability is difficult to attain due to common requirements of predictability and high efficiency for real time kernels and application ....

D.R. Cheriton, M.A. Malcolm, L.S. Melen, and G.R. Sager. Thoth, a portable real-time operating system. Comm. of the Assoc. Comput. Mach., 22(2):105--115, Feb. 1979.

....kernel support has caused Unix programmers to implement a variety of coroutine packages to support multi stack applications. Lightweight threads of control can allow a programmer to encapsulate computations with their stack state and thus achieve greater modularity. Research systems, such as THOTH [2] and its successor, Stanford s V Kernel [3] have shown that multiple threads of control within a single process can be an especially important tool for writing server applications. A thread package could provide an attractive way to take advantage of the parallelism afforded by tightly coupled ....

D. R. Cheriton, M. A. Malcolm, L. S. Melen, and G. R. Sager. Thoth, a Portable Real-Time Operating System. Communications of the ACM :105-115, February, 1979.

....as to avoid the loss of data coming in on external devices. Allowing the device interrupt handler to at least buffer the data will save the data from being lost. In real time systems, the maximum critical region is carefully bounded so that the response time to external interrupts can be bounded [2]. For example, the scheduler in iRMX uses additional data structures and software locking to avoid disabling interrupts for long periods of time when manipulating internal lists of arbitrary length [12] Other incentives for increased preemptibility (or, equivalently, the reduction of the size of ....

D. R. Cheriton, M. A. Malcolm, L. S. Melen, and G. R. Sager. Thoth, a Portable Real-Time Operating System. CACM, 22(2):105--115, February 1979.

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