Figure 1-1 [1]The principle guiding the development of the KeyTECH system was to provide a portable extension to modern computer hardware that transformed the hardware interface into one which was better suited to the sophisticated application systems both planned and under development. The resulting KeyTECH architecture consists of two basic parts: the platform and a number of application environments that run on that platform.
KeyTECH is a software platform upon which a variety of applications and application environments run. It consists of a kernel, which runs in the privileged state of the machine, and small set of non-privileged objects. This platform provides the fundamental functions of most modern operating systems. These functions can be classified as the Physical Resource Manager and include: real memory management, DASD management, and CPU management.
Figure 1-1 illustrates this platform concept. It is the intention of this manual to provide a basic understanding of how environments are built and applications are run on top of this platform.
Figure 1-1 [1]
The programming environment presented by this platform supports Objects and Capabilities. Objects are an embodiment of the Physical Resource Manager in that they each have a separate virtual address space of extremely large size (48 bit address) and are separately scheduled. The small set of objects that are part of the KeyTECH platform provide for space management, timer services, and other fundamental system services.
It is upon the KeyTECH platform that applications and application environments run. Those which are designed to make direct use of KeyTECH facilities are called native environments. Those which were designed for other hardware and operating system facilities, but which are supported on the KeyTECH platform, are called guest environments. Since the platform provides the basic services of most modern application environments, it is easy to simulate these guest environments on the KeyTECH platform. Because the underlying platform also provides for basic communication and data sharing facilities, it is possible to have applications in multiple environments running simultaneously and sharing data.
An underlying principle of building application environments on the KeyTECH platform is that of allowing KeyTECH to handle all aspects of multi-tasking, memory management and I/O management. Often this means that each application in a simulated environment is supported by a private instance of the environment. KeyTECH supports "instantiation" of its objects in much the same way as a "type manager" in object-oriented languages support instances. Instances of the same KeyTECH object have their own address space, are scheduled separately, yet share a single copy of the code. This facility allows KeyTECH to handle all aspects of multi-tasking. This single principle is responsible for much of the ease of development of guest environments.
Key Logic has designed and built two native environments which run on the KeyTECH platform. These environments are designed to support applications which take advantage of the fundamental features of the KeyTECH platform: capabilities and object orientation. By combining Objects with Capabilities, these environments allow the development of efficient and sophisticated application systems.
Key Logic has designed support for a number of guest environments and has implemented three of them. These guest environments support applications which were designed to meet the specifications and functionality provided in the original environment without having to alter the application code. Often it is possible to enhance the application code in such a way as to combine guest environment compatibility with the ability to communicate directly with objects using capabilities. For instance, function and data in one environment can be made available to applications in another environment. This provides a powerful tool for application growth.
Figure 1-2 illustrates several of these environments operating simultaneously on a KeyTECH platform.
Use of application environments do not impose a layer of software between the application and the KeyTECH platform. The application runs in a KeyTECH supported object and executes native System/370 instructions until it requires a system service that is normally provided by the operating system for which the application was designed. When the system service is requested, a message is sent to another KeyTECH object that is emulating the guest environment. This "environment emulating object" either performs the required service directly or sends messages to other KeyTECH objects to provide the service.
If desired, the guest application source code can be easily modified so that the application can directly access KeyTECH objects that supply basic services such as data files, timer services, and communication services. Since all KeyTECH objects run directly on the KeyTECH platform and can be reached directly by any other object, system services are delivered directly to applications without going through some imposed system hierarchy.
Figure 1-2
Guest applications are generally run in their own address space, even if the application running in the real environment would have shared its address space with other applications. Multi-tasking is accomplished by replicating the application and its guest environment emulator so that each task is separated from all other tasks. This instantiation into distinct objects increases the overall reliability of a complex application, even when the application itself contains bugs. Individual instances of the application may encounter the bug without affecting other instances, which are running the same application code but are servicing other tasks.
Data sharing is accomplished by using KeyTECH mechanisms that can insure the proper isolation. Many copies of an application can share read-only memory and read-write memory as required. Applications that share read-write memory are not as isolated from interference with each other as are those that share only read-only memory. Data can be passed quickly and efficiently between applications using the capabilities provided by KeyTECH.
The remainder of this document discusses the architectural components which facilitate the creation of and support of such diverse environments on a single platform - even some which are not "native" to the System/370. Specific examples of guest environments will be examined in some detail to illustrate how these components are combined.