burroughs 1051752 B6500 Basic IO Handling Oct 69 free download

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Reprinted from: Proceedings of 2nd ACM Symposium on Operating Systems Principles a.iin i Patel Princeton, New Jersey October, 1969 M. R BASIC I/O HANDLING ON BURROUGHS B6500 Rajani M. Patel Burroughs CorporationPasadena, California Summary: The approach to processing basic Input/Output in B6500 hardware design and software implementation is discussed in this paper. Hardware I/O structure necessary to the understanding of the approach is described first. The represen- tation of the I/O queue and the algorithms used in handling I/O requests are described in detail to emphasize the ease with which the I/O handling portions of the executive system may be modified to suit any installation. Some of the I/O tables for coordinating I/O activity are discussed. The concept of asynchronous processes running as extended arms of the executive system is discussed and the implementation of it for updating status of peripheral units, for handling I/O errors, etc. is described. The usage and implementation of I/O related events and software interrupts is discussed. The locking concept is presented. Finally, the complete I/O initiation and completion cycle is described. The description throughout this paper is based on the actual working system implemented with language ESPOL -an extended ALGOL language used for writing executiv~ systems. Some of the special language constructs pertinent to I/O handling are illustrated. INTRODUCTION The B6500 stack organization is designed for process switching and makes its operation efficient for a multiprogramming/multiprocessing environment. To com- plement the hardware design, events and queues are implemented in the software for inter-process communication and deactivation and activation of a process during an I/O cycle or because of preemption. This paper describes how the basic I/O needs are satisfied in such a process-orientedenvironment. The term 'process' in B6500 System is easy to understand if it is remembered that the process has its own stack to run. Excep~ for some minor imp