SODA--A Dual Activity Operating System

In order to understand the basic features and somewhat tortuous principles of the SODA, several words must be devoted to a brief description and history of ODRA-1204. A standard ODRA-1204 is a small scientific computer whose main characteristics are collected in Table 1. Originally, this computer was designed as a general purpose computer with all features necessary for timeshared BDP applications. Later on, the Elwro Factory decided to introduce another computer specifically for BDP and to market a truncated version of the original machine as a scientific computer ODRA-1204. This bit of history explains the very unusual and imbalanced characteristics of the machine which has full interrupt and memory protection facilities, single I/O channel,! no tapes and relatively small backing store on magnetic drums. The aim of the SODA designers was very simple—to build an operating system which, while making use of the advanced features of the computer hardware (which would have been idle in a traditional one-user-at-a-time running system), would not actually limit the throughput characteristics (which could easily happen if standard solutions were applied). At the same time, the designers aimed at an operating system reasonably well suited to the research institute environment in which the computer was to be used. In other words, the SODA is a compromise between several antagonistic tendencies, subject to rather severe restrictions imposed by certain austerity of the hardware configuration. The conflicting tendencies are: (i) sustained high throughput, i.e. a development towards batch-processing of a sort, (ii) short turn-around time for small programs and frequently many compilations for a single production run, i.e. a development towards easily accessible on-line system, (iii) prevailing desire to utilise as fully as possible the interrupt, memory protection and autonomous data transmission features