Two-Bank Programs on ND-100¶

How to split a program's code and data into separate address banks — which languages support it, how to turn it on at compile time, and how to link and run the result.

Everything in this document is sourced from real Norsk Data manuals already in this repo (mainly Developer/MON/Monitor Calls.md, the SINTRAN III Monitor Calls manual) — not inferred. Where a claim could not be confirmed against a real source, it is marked [unverified].

1. What a "bank" is, and why a program would need two¶

The ND-100 is a 16-bit machine: a 16-bit register addresses at most 64K words directly. That 64KW unit is a bank — this is the same "bank" the rest of this repo's memory-architecture notes use for the CPU's 24-bit physical address space (256 banks × 64KW). A program that fits code and data together in one bank is a one-bank program. A program too big for that, or one that simply wants code and data kept in separate address spaces, becomes a two-bank program — one bank for instructions, a second bank for data — which is why the SINTRAN Monitor Calls manual states the concrete numbers plainly:

"The address area on ND-100 is 128 Kbytes for one-bank programs and 256 Kbytes for two-bank programs." — SINTRAN III Monitor Calls manual (this repo: Developer/MON/Monitor Calls.md)

(128 Kbytes = 64K words = one bank; 256 Kbytes = 128K words = two banks — words, not bytes, is this repo's primary unit for ND-100 memory, per the project's own convention.)

2. How you turn it on, per language — real, cited evidence¶

There is no single universal switch. Each language compiler has its own way of asking for two-bank code, and the choice always shows up twice: once as a compile-time setting, and again as which pair of runtime library files you feed to the linker afterward (BRF-Linker on ND-100 — see LINKING-GUIDE.md). The two must agree — a program compiled for one bank linked against 2-bank libraries (or vice versa) is exactly the failure mode the SINTRAN error table warns about (see §4 below).

Language	Compile-time switch	1-bank link libraries	2-bank link libraries	Source
FORTRAN (100)	`SEPARATE-DATA ON` before `COMPILE`, when the program needs more than 128 Kbyte	`MON-CALL-1BANK:BRF`, `FORTRAN-1BANK:BRF`	`MON-CALL-2BANK:BRF`, `FORTRAN-2BANK:BRF`	`Monitor Calls.md`, §1.4, verbatim
PLANC (100)	`SEPARATE-DATA ON` before `COMPILE`, same trigger as FORTRAN	`MON-CALL-1BANK:BRF`, `PLANC-1BANK:BRF`	`MON-CALL-2BANK:BRF`, `PLANC-2BANK:BRF`	`Monitor Calls.md`, §1.5, verbatim
Pascal (CAT-PASCAL, ND-100)	`$OPTION B2` compiler command, before `$COMPILE`	(not shown — the example only demonstrates the 2-bank form, `CAT-2BANK`/`CAT-FREE`)	`CAT-2BANK:BRF`, `CAT-FREE:BRF`	`Monitor Calls.md`, §1.2, verbatim — note this example is for the newer CAT-PASCAL compiler ("version A"), explicitly NOT the older `PASCAL-100`/`PASCAL-500` compilers the manual tells you not to use
COBOL (100)	not stated in the source read — the example links `MON-CALL-2BANK:BRF`/`COBOL-2BANK:BRF` directly, with no accompanying "before COMPILE" command shown the way FORTRAN/PLANC have. `[unverified]` whether COBOL needs an explicit compile-time flag at all, or whether 2-bank is purely a link-time choice for this language	(not shown in the excerpt read)	`MON-CALL-2BANK:BRF`, `COBOL-2BANK:BRF`	`Monitor Calls.md`, §1.3, verbatim
C (CC-100)	none found in any source read — every example (including the real `CSESSION:MODE` install-time smoke test decoded from the ND-10760A CC-100 floppy) only shows the link-time choice	(not attested — CC-100's shipped example only uses the 2-bank set)	`CC-2HEADER`, `CC-2BANK`, `CC-2TRAILER`	`CSESSION:MODE` (decoded from the real floppy) + this repo's `C-DEVELOPER-GUIDE.md`
NPL	Existing `NPL-DEVELOPER-GUIDE.md` text (not sourced to a manual — `[unverified]`) shows `1BANK`/`2BANK` assembler-level directives used inline around a memory-bank-switching code pattern. This looks like a different mechanism from the other languages' single global compile-time switch — it reads as a per-section placement directive (and the surrounding example is about runtime register-level bank switching via `*TRR 10`, not necessarily the same "program compiled as one unit spanning two banks" concept above). Do not assume it is interchangeable with `SEPARATE-DATA ON`/`$OPTION B2` without checking the actual NPL/MAC manual.	unknown	unknown	`NPL-DEVELOPER-GUIDE.md` (unverified in-repo text, not a manual citation)
MAC/FMAC (System package)	n/a — MAC assembles what you write; bank placement is the programmer's own responsibility via addressing, not a compiler switch	—	—	inferred from MAC's nature as an assembler, not compile-flag driven

Do not extrapolate this table to languages/products not listed — SIBAS, BASIC, and the ND-500-hosted compilers (which don't have a PROG/BPUN or bank concept at all — see LINKING-GUIDE.md §8) have not been checked for this document.

3. The full build sequence, worked example (FORTRAN, verbatim from the manual)¶

@FORTRAN-100
FTN: STANDARD-CHECK OFF
FTN: COMPILE EX-PROG:SYMB, EX-PROG:LIST, EX-PROG:BRF
FTN: EXIT

@BRF-LINKER
Br1: PROGRAM-FILE EX-PROG:PROG
Br1: LOAD EX-PROG:BRF, MON-CALL-1BANK:BRF, FORTRAN-1BANK:BRF   % 1-bank, default
Br1: EXIT

@EX-PROG

If the program is too big for one bank (128 Kbyte), the only things that change are: give SEPARATE-DATA ON before COMPILE, and swap in the 2-bank libraries at link time:

@FORTRAN-100
FTN: STANDARD-CHECK OFF
FTN: SEPARATE-DATA ON
FTN: COMPILE EX-PROG:SYMB, EX-PROG:LIST, EX-PROG:BRF
FTN: EXIT

@BRF-LINKER
Br1: PROGRAM-FILE EX-PROG:PROG
Br1: LOAD EX-PROG:BRF, MON-CALL-2BANK:BRF, FORTRAN-2BANK:BRF   % 2-bank
Br1: EXIT

@EX-PROG

PLANC follows the identical shape (SEPARATE-DATA ON before COMPILE, then MON-CALL-2BANK:BRF+PLANC-2BANK:BRF at link time) — see Monitor Calls.md §1.5 for the verbatim example this is drawn from.

Pascal instead sets the option at the very top of the compile session:

@PASCAL
$OPTION B2
$COMPILE EX-PROG:SYMB, "EX-PROG:LIST", "EX-PROG:BRF"
*EXIT
@BRF-LINKER
Br1: PROGRAM-FILE "EX-PROG:PROG"
Br1: LOAD EX-PROG:BRF, CAT-2BANK:BRF, CAT-FREE:BRF
Br1: EXIT
@EX-PROG

4. What happens if you get it wrong — real runtime warning codes¶

The SINTRAN error/message table (Monitor Calls.md) documents exactly this failure mode:

Code (octal)	Code (decimal)	Meaning
307	199	Warning: 2-bank prog. file, but segment is only 1-bank
310	200	Warning: no such page in data bank, program starts as 1-bank

Both are about the background segment size, not the compile/link step — a two-bank program needs a big enough terminal/RT background segment to actually hold both banks at runtime. This repo has two independently-verified examples of the exact command and size needed: ND-10076J Pascal and ND-210721C BRF-Linker both require

@CHANGE-BACKGROUND-SEGMENT-SIZE <terminal number>,128

(128 here is K-words, i.e. 256 Kbytes — matching the two-bank address-area figure in §1.) Run this (once per terminal, or scripted at login) before running a two-bank program; skipping it is what produces warning 307/199 above.

5. Open items¶

Confirm whether COBOL genuinely has no compile-time flag for 2-bank, or whether the manual page showing it simply wasn't captured in the excerpt read for this document.
Confirm whether C (CC-100) has any compile-time flag at all, or whether bank selection is purely a link-time library choice for that language — no source read so far shows a C-side switch.
Resolve what NPL's *1BANK/*2BANK directives actually are and whether they relate to this document's topic at all — the existing NPL-DEVELOPER-GUIDE.md text is not sourced to a manual.
ND-500 has no bank concept (flat, much larger address space per segment — see LINKING-GUIDE.md §2.5); this document is ND-100-only.