TOPS20 MonitorInternals 1978

The document "DECSYSTEM-20 SWS MONITOR INTERNALS MONITOR TABLES PRELIMINARY VERSION" provides flowcharts and descriptions of key internal monitor functions for the DECSYSTEM-20 operating system, specifically focusing on its Software Working Set (SWS) monitor.

The document is organized into several main sections:

1. Scheduler Flowcharts: Details the scheduling process, including context switching, process control, accounting, clock updates, and job management (startup, selection, garbage collection, balance set adjustment).
2. Page Fault Handling Flowcharts: Covers the processes involved in managing page faults, such as accounting for traps, local garbage collection, swapping pages, checking in-core size limits, and determining the cause and resolution of different trap types (e.g., illegal read/write, age-related traps).
3. JSYS Call Flowcharts (Device Independent Level): Describes general system calls that are not tied to a specific device, including functions for file management (Get JFN, Open File, Close File, Map File or Fork, Update File Pages) and sequential I/O (Input/Output, Byte Transfer).
4. JSYS Call Flowcharts (Disk Dependent Level): Focuses on system calls specific to disk operations, such as disk opening/closing, assigning/updating/releasing OFNs, and sequential input/output for disk.
5. JSYS Call Flowcharts (Magtape Dependent Level): Details system calls for magtape operations, including opening/closing, sequential input/output, and queuing IORB requests.
6. Requesting Disk/MTA I/O & Interrupt Handling (Physio Level): Explains the lower-level physical I/O requests for disk and magtape, including queuing IORBs, starting unit positioning/transfer, and handling interrupts for these devices.
7. JSYS Calls (TTY Dependent Level): Describes system calls specific to Teletype (TTY) devices, including opening/closing, sequential input/output, and character-level operations.
8. Requesting TTY I/O & Interrupt Handling (DTE Protocol Handler): Details the procedures for handling TTY output requests and interrupts, including queuing output, processing RSX20F packets, and managing internal DTE operations.

The document also includes detailed comments and descriptions for various tables used by the monitor, such as ALOC1/ALOC2 (disk quotas), BALSET (balance set table), BAT (bad allocation table), CDB (channel data block), CST (core status tables), DEVCHR (device characteristics), DSKSIZ (disk size pointers), DST (drum status table), DTE (storage for DTEs), FDB (file description block), FKINT/FKINTB (fork interrupt tables), FKJOB (fork job table), FKNR (fork reserve pages), FKPGS (fork page and process storage), FKPT (fork list pointer), FKSTAT (fork status table), FKTIME (fork time table), FKWSP (fork working set), HOM (home block), HOMTAB (channel/unit mapping), INDEX (index block), IORB (I/O request block), LPT (line printer storage), PSB (process storage block), SPT/SPTH/SPTO (special pages tables), SSIZE (subsystem working set size), STRTAB (structure data block table), TTBFRC (teletype buffer control), TTBUFS (teletype buffers), TTCS (teletype control state), TTDPSI (teletype deferred pseudo interrupt), TTE (teletype echo output buffer), TTFEWD (teletype front end word), TTFLGS (teletype flags), TTFORK (teletype fork table), TTI (teletype input buffer), TTLINK (teletype linked lines), TTLPOS (teletype line position), TTMOD1 (teletype mode), TTO (teletype output buffer), TTPSI (teletype pseudo interrupt), TTSPWD (terminal speed word), TTYPE (teletype type), UDB (unit data block), and UDIORB (UDSKIO IORB pool).

Overall, this document serves as a comprehensive technical reference for understanding the internal workings, data structures, and operational logic of the DECSYSTEM-20 SWS monitor.