PiDP-8/I Software

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## Criteria

This survey does not include every PDP-8 assembler, on purpose. This is not a comprehensive survey, it is not a genealogy project, and it is not an advocacy platform. Our purpose here is to list useful options for the practicing PDP-8 assembly language programmer.

The assemblers listed meet these criteria:

*   Runs on the PiDP-8/I.

*   It is readily available online.

*   It offers a valuable capability to the end user:

    *   It is the back end assembler for some other language which is itself important.
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## PAL-III

| **Introduced** | 1965
| **Manual** | [PDF, 790 kB](http://www.telegraphics.com.au/doc/paliii.pdf)
| **Delivery** | paper tape

The PAL-III assembler shipped on [punched paper tape](https://en.wikipedia.org/wiki/Punched_tape) as part of the grandiosely-named "PDP-8 Assembly System." This amounted to an assembler, an editor, a debugger, and a loader, each a separate paper tape. The programmer would first toggle in the RIM loader, then use that to load the BIN loader from yet a fifth paper tape, then run each of these tapes through the paper tape reader repeatedly in order to iterate his way toward a working program! The assembler itself required multiple passes through the reader: at least two in order to produce a computer-readable BIN format output tape, or more if the programmer also wanted a human-readable listing output on the terminal.
The PAL-III assembler shipped on [punched paper tape](https://en.wikipedia.org/wiki/Punched_tape) as part of the grandiosely-named "PDP-8 Assembly System." This amounted to an assembler, an editor, a debugger, and a loader, each a separate paper tape. The programmer would first toggle the RIM loader into the PDP-8's front panel, then use that to load the BIN loader from yet a fifth paper tape, then run each of these tapes through the paper tape reader repeatedly — reusing the still-in-core BIN loader each time — in order to iterate his way toward a working program!

The assembler required at least two passes through the tape reader in order to produce a computer-readable BIN format output tape, and up to four depending on the additional output options the programmer wanted, such as a listing on the terminal.

If you look at pictures of PDP-8 computers, you can often see a blue tray with narrow slots in it, each meant to hold one of these key paper tapes, as they were needed near at hand when using the computer. There is a good picture of one on [the cover of the 1974 edition of the OS/8 Handbook](https://archive.org/stream/bitsavers_decpdp8os8_39414792/OS8_Handbook_Apr1974?ui=embed#page/n0/mode/1up).
If you look at pictures of PDP-8 computers, you can often see a tray with narrow slots in it, each meant to hold one of these key paper tapes, as they were needed near at hand when using the computer. There is a good picture of a blue one on [the cover of the 1974 edition of the OS/8 Handbook](https://archive.org/stream/bitsavers_decpdp8os8_39414792/OS8_Handbook_Apr1974?ui=embed#page/n0/mode/1up).

PAL-III can be considered the baseline assembler for a PDP-8, since almost every PDP-8 at least included some kind of paper tape reader, and most of the other assemblers for the PDP-8 share its basic syntax.
PAL-III can be considered the baseline assembler for a PDP-8, since almost every PDP-8 at least included some kind of paper tape reader, and most of the other assemblers surveyed here share its basic syntax.


## MACRO-8

| **Introduced** | 1965
| **Manual** | [PDF, 1.7 MB](https://www.grc.com/pdp-8/docs/MACRO-8_Programming_Manual.pdf)
| **Delivery** | paper tape
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PAL-D is basically PAL-III for the [PDP-8 Disk Monitor System](https://en.wikipedia.org/wiki/4K_Disk_Monitor_System), one of OS/8's predecessors.


## The OS/8 Assemblers

| **Introduced** | 1971
| **Manual** | most any OS/8 manual, such as [the 1974 edition](https://archive.org/details/bitsavers_decpdp8os8_39414792)
| **Manual** | most any OS/8 manual, such as [this 1974 edition][os8m]
| **Delivery** | part of OS/8

[OS/8](https://en.wikipedia.org/wiki/OS/8) was [the primary programming system from DEC][faq10] for the PDP-8 in its later years. It included several different assemblers, all documented in its manual, one edition of which is linked above.

The introduction date is that of OS/8, but OS/8 has a [complicated development history][faq10] that stretches back to 1966 or so. I do not mean by this grouping to imply that they were all created and introduced at the same time. As historical evidence arrives, I will make finer distinctions in the dates. Until then, we have a years-wide window for each of these OS/8 assemblers' creation dates: after PAL-III (1965) and before 1974, the publication date of the linked manual.

[faq10]: http://www.faqs.org/faqs/dec-faq/pdp8/section-10.html
[os8m]: https://archive.org/details/bitsavers_decpdp8os8_39414792


### PAL8

PAL8 is basically a direct replacement for PAL-III under OS/8. As such, I think it is fair to consider it the default assembler for the PDP-8, two ways: 
PAL8 understands the same basic language as PAL-III and generally has more features, most especially related to running under OS/8, such as the ability to set options via OS/8's command interpreter (CCL) rather than via the PDP-8's front panel switches.

I consider it the default assembler for OS/8 users. If none of the information below guides you to one of the other assemblers, you should probably start with PAL8. If you have a piece of assembly code that is meant to be assembled under OS/8, and you have no evidence that is for any other assembler, it's probably meant to be assembled by PAL8.
First, if you're using OS/8 and have no better idea of which assembler to use, you should probably start with PAL8.

PAL8 has several features not present in PAL-III:

*   it can output [CREF and DDT][os8m]-compatible output files
*   in addition to `+` and `-` in expressions, it allows:
    *    `^` for 12-bit unsigned multiplication (`*` was already taken for setting the location counter)
    *    `%` for 12-bit unsigned division (`/` was already taken as the comment start character)
    *    `!` for Boolean OR (the ASR-33 terminal supported [a 64-character subset of printable ASCII](http://iclces.uk/articles/a_teletype_font.html), which did not include ¦)
    *    `&` for Boolean AND
Second, if you have a piece of assembly code that is meant to be assembled under OS/8, and you have no evidence that is for any other assembler, it's probably meant to be assembled by PAL8.

PAL8 is missing one feature present in PAL-III: the ability to get a brief listing of the undefined symbols in a program. The information is instead presented inline in the listing output, not grouped together into a single place, which can make refinement of an in-development program tedious as you need to comb it out of the other output.


### RALF/FLAP

RALF is the back-end assembler for OS/8's FORTRAN IV compiler. As a result of that support role, it has several notable advantages over PAL8:

*   relocatable output code

*   easy access to the optional [floating-point processor](http://dustyoldcomputers.com/pdp12/fpp12.html)

The RALF assembler has a mode switch that causes it to generate absolute-addressed code. In this mode, it is called FLAP.


### SABR

As RALF is to OS/8's FORTRAN IV compiler, so [SABR](http://homepage.cs.uiowa.edu/~jones/pdp8/faqs/#langs) is to OS/8's FORTRAN II compiler. SABR is closer in feature set to PAL8, since FORTRAN II does not assume that you have a floating point processor, and it is not capable of all the relocation and overlay tricks that OS/8's FORTRAN IV compiler is.

A programmer may use SABR one of three ways:

1.  Implicitly as the back-end of the OS/8 FORTRAN II compiler
2.  Via inline assembly code in a FORTRAN II program
3.  Directly.

The third option indirectly still depends upon FORTRAN II because SABR writes its `*.RL` output files with the assumption that they will be linked to the FORTRAN II runtime and libraries by the OS/8 `LOADER` program, so the generated code makes use of those facilities.

[Ian Schofield's CC8 compiler][cc8] compiler also operates like the OS/8 FORTRAN II compiler, emitting SABR output and depending upon the FORTRAN II library and runtime. Inline assembly via `#asm` is sent as-is to SABR.

[cc8]: /doc/trunk/src/cc8/README.md


## MACREL

| Introduced | 1980
| Manual | [text, 384 kB](http://vandermark.ch/pdp8/uploads/PDP8/PDP8.Manuals/AA-J073A-TA.txt)
| Delivery | DECtape for OS/8

Although this is technically another OS/8 assembler, its late introduction, separate documentation, and separate distribution from OS/8 proper require that we consider it separately.

Aside from MACRO-8, none of the assemblers above support macros, a very helpful feature in assembly language programming. MACRELs was intended to be DEC's solution to that problem in the disk-based operating system era.
Aside from MACRO-8, none of the assemblers above support macros, a very helpful feature in assembly language programming. MACREL was intended to be DEC's offered solution to the want of a macro assembler for the PDP-8 in the disk-based operating system era.

Unfortunately, it never achieved widespread use outside of DEC.


## palbart

| **Introduced** | 1996
| **Manual** | [man page](http://manpages.ubuntu.com/manpages/artful/man1/palbart.1.html)
| **Delivery** | Internet, PiDP-8/I project

This assembler was written by Gary A. Messenbrink — and later enhanced by several others — to support the fleet of PDP-8/e computers in the [Bay Area Rapid Transit](https://en.wikipedia.org/wiki/Bay_Area_Rapid_Transit) system, thus the name.
This assembler was written by Gary A. Messenbrink — and later enhanced by several others — to support the fleet of PDP-8/e computers in the [Bay Area Rapid Transit](https://en.wikipedia.org/wiki/Bay_Area_Rapid_Transit) system; thus the name.

We ship a version calling itself "pal-2.13, 03 May 2015" as part of the PiDP-8/I project. If you place a `*.pal` file in either its `asm` or `examples` subdirectories, then type `make`, the project's build system will generate several output files:
We ship a version calling itself "pal-2.13, 03 May 2015" as part of the PiDP-8/I project. If you place a `*.pal` file in either its `asm` or `examples` subdirectories, then type `make`, the project's build system will generate several output files named after the input file:

*   **<code>obj/*.lst</code>** — the assembler's text listing output, giving the assembled machine code alongside the source code, plus any error messages
*   **<code>bin/*.pt</code>** — the machine code output in RIM paper tape format, suitable for loading into SIMH's PDP-8 simulator
*   **<code>boot/*.script</code>** — a SIMH init script that deposits the machine code into the PDP-8 simulator's core memory and starts it running; pass the file name to `bin/pidp8i-sim`


## pdpnasm

| **Introduced** | 2006
| **Manual** | refers to PAL-III documentation, then gives exceptions on its [home page][pdpnasm]
| **Manual** | see its [home page][pdpnasm]
| **Delivery** | [Internet][pdpnasm]

This is a PDP-8 assembler accepting the PAL-III syntax for Unix type systems. 

I am listing it here along with `palbart` because there are [known weaknesses in `palbart`](/rptview?rn=4). If you know of more, please [file them](/tktnew). `palbart` currently has no central development home, so it is possible that the PiDP-8/I project will end up hosting an improved version.

Meanwhile, it seems like a good idea to me to have a second option at hand when cross-compiling code on a POSIX type platform for a PDP-8. 

[pdpnasm]: http://people.csail.mit.edu/ebakke/pdp8/


## License

Copyright © 2017 by Warren Young. This document is licensed under the terms of [the SIMH license][sl].

[sl]: https://tangentsoft.com/pidp8i/doc/trunk/SIMH-LICENSE.md