LOS Support Code - BCL Molecular 18

BCL Molecular 18
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This template is adapted at each installation to define the available peripherals, allocate the available memory and locate the System Catalogue.
This template sets out the installation's dynamic data LOS needs to retain across re-boots. Applications may add their own control data to the System Control Record, which is permanently "cached" at 00/0477 to 00/1177 in Zero Page and is thus directly accessible to all tasks. This data is likely to include File Status Blocks, latest Serial Numbers, Control Balances, Stock Balances, VAT rates and so forth. When any such control data is updated the record must be committed to disc by JSBR IZ 1667 Stow System Control Record. As this is properly the last in any uninterruptible sequence of committals to disc, stowing the Control Record may be considered similar to making a UNIX sync system call (though in practice LOS commits each individual disc write to disc before resuming the calling task).
This is the area reserved for system use in the topmost column of each task partition (in a modern Object Orientated implementation this would be the private and protected data of the Task object).
13 sectors comprising system utilities LIST, PMAP, ZERO, READ, R, OP, HALT and CDL. The OP utility relocates itself in the task buffer areas (3200- to 3677-) thus enabling any overlay module to be amended at its runtime offset within the task's overlay area (0000- to 3177-).
1 sector implementing Copy Sectors. Loads into 3000- to 3177-.
4 sectors implementing Disc Security. Loads into 2000- to 2777-. Calls the Copy Sectors overlay (see above) and uses 0000- to 1777- as the 1K transfer buffer.
This module is "fine tuned" at each installation to ensure various system utilities respond appropriately.  This Includes Line-up Command parameters for each print queue, the table of file names for the SE utility and entry points for the Disc Security programs.
5 sectors implementing the System Enquiry utility.
5 sectors comprising system utilities FLAG, KICK, DAY, DATE and RP (Reprint document).
An optional system module (written in 1987) to implement the Sort utility.
Implements the MEND utility within the On-line Security option.
An optional system module (written in 1983) to implement "Dynamic Data Exchange" between the Molecular 18 computer and compatible terminal emulation software on a microcomputer or PC.

(C) 2022 Kevin Murrell & The National Museum of Computing
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