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Architecture

The H1OS Operating System consists of a Kernel and a set of Service Processes.

The Kernel is a set of independent routines providing basic functionality such as memory allocation and low-level access to peripherals. These routines are invoked from applications by the mean of "system calls" consisting of software interrupts. Kernel routines are said to be "critical" as they must execute from top to bottom without interruptions hence they must be designed to return rapidly in order to avoid system "freezing". Among these Kernel routines is the processes Scheduler.

Service processes are long-term execution programs sharing a time-sliced space that we call the "Multiprogramming Space" (MPS) under the Scheduler's control. As opposite, we define the notion of "Kernel Programming Space" (KPS) to refer to the "critical-region" code occurrence. Application and OS Service Processes share the same MPS. Among Service Processes is the commands interpreter or Monitor which provides the human interface for the Operator.

A key distinction between KPS and MPS code is that the former utilizes fixed global variables located in a dedicated portion of the memory addressing space that we call the "Kernel Data Area" whereas the later utilizes memory granted by the OS upon request, located in the Heap.

Apart from the Kernel, Monitor and OS Services, the Operating System allows for installable Run-Time Libraries (RTL) such as those provided by languages. RTL code is placed in the Heap and executes either in the MPS or the KPS as we shall see later.