PiDP-8/I Software

*   `DEFINE` macro definition system
*   automatic off-page link generation
*   literals in the current page via `(NN)` syntax or in page zero via `[NN]`; closing paren/bracket optional
*   more operators in expressions:
    *    `!` for Boolean OR (the ASR-33 terminal character set [did not include the ¦ character][cs33])
    *    `&` for Boolean AND
*   single-character ASCII constants: `"A`
*   single-character ASCII constants: `"A"`; closing quote optional
*   other new pseudo-ops:
    *   `DUBL`: define double-precision integer constant
    *   `FLTG`: define double-precision floating-point constant
    *   `PAGE`: [re]set the location counter to the top of the given page
    *   `TEXT`: convert a literal string in the program text to 6-bit packed ASCII in the binary output

The `DEFINE` feature is clearly this assembler's marquee feature, but it is the rest of the list that should open your eyes: all of these features except for `DUBL` and `FLTG` were later adopted as-is into the PAL family.

4K PAL-D added only one new feature to the PDP-8 assembler family: the `XLIST` pseudo-op, which lets the programmer stop and then re-start the assembly listing in the optional third pass.

4K PAL-D is more notable for the features it brought into the PAL family from [MACRO-8](#macro-8):

*   literals
*   off-page link generation
*   Boolean operators in expressions
*   the `PAGE` and `TEXT` pseudo-ops
*   more operators in expressions:
    *    `!` for Boolean OR (the ASR-33 terminal character set [did not include the ¦ character][cs33])
    *    `&` for Boolean AND

8K PAL-D added several more features relative to the 4K version:

*   ability to run in 8K or 12K of core, allowing assembly of larger programs
*   more pseudo-operations:
    *   `EJECT`: emit a form feed in the listing output
    *   `IFDEF` and `IFZERO`: conditional assembly tests; affected statements in angle brackets
    *   `NOPUNCH` and `ENPUNCH`: stop and restart assembled machine code output
    *   `ZBLOCK`: reserve memory, setting initial values to zero

Note that neither version of PAL-D brought over the `DEFINE`, `DUBL` or `FLTG` pseudo-ops from MACRO-8.

Notice also that the negated forms of the conditional assembly operations did not appear until later. The first reference I've been able to find for `IFNZRO` and `IFNDEF` is in connection with [PAL8](#pal8).

We find evidence for a complicated development history in the `PUNCH` and `XLIST` pseudo-ops. They do much the same thing, only for different passes of the assembler, yet the form of the ops differ.  If this assembler was created by a single mind in a single time and place, or if it were created by a standards committee with a mandate to simplify and unify, you would expect these two sets of pseudo-ops to have similar names and forms, either `XPUNCH` taking an argument or a `NOLIST`/`ENLIST` pair. We can infer different minds behind the 4K and 8K versions of PAL-D.

The `PUNCH` op names also suggest that the operation is mainly useful for paper tape output, still an important I/O device when PAL-D was new. We can find it mentioned in the PAL8 section of [the OS/8 Handbook (1974 ed.)][os8m], but it was airbrushed out of history by the [1979 edition for OS/78][os78m], suggesting that the purpose of these pseudo-ops became effectively redundant after the bulk of the market moved to disk-based PDP-8 systems such as the [DECstation 78][ds78], a microcontroller based PDP-8 merged with a VT52 video terminal, which effectively replaced the teletype + paper tape reader/punch most often used with earlier PDP-8 systems. (Thus the renaming of "OS/8" to "OS/78," by the way.)
The `PUNCH` op names also suggest that the operation is mainly useful for paper tape output, still an important I/O device when PAL-D was new. We can find it mentioned in the PAL8 section of [the OS/8 Handbook (1974 ed.)][os8m], but it was airbrushed out of history by the [1979 edition for OS/78][os78m], suggesting that the purpose of these pseudo-ops became effectively redundant after the bulk of the market moved to disk-based PDP-8 systems such as the [DECstation 78][ds78], a microcontroller-based PDP-8 merged with a VT52 video terminal, which effectively replaced the teletype + paper tape reader/punch most often used with earlier PDP-8 systems. (Thus the renaming of "OS/8" to "OS/78," by the way.)

Like MACRO-8, PAL-D does not have the `FIXMRI` pseudo-op.

[cs33]: http://iclces.uk/articles/a_teletype_font.html
[ds78]: https://en.wikipedia.org/wiki/DECstation#DECstation_78


## <a id="os8"></a>The OS/8 Assemblers

| **Introduced** | 1971
| **Manual** | most any OS/8 manual, such as the [OS/8 Handbook][os8m] (1974 ed.) or its [successor for OS/78][os78m] (1979 ed.)
| **Introduced** | 1971, collectively
| **Manual** | most any OS/8 manual, such as the OS/8 Handbook: [1974 ed.][os8m] or [1979 ed. for OS/78][os78m]
| **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.
[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 handbook; two of its many editions are 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. Some of the following assemblers predate OS/8; where the dates for them are known, they are called out. For those with no additional date information, it is possible that it was first introduced after OS/8 but before 1974, the date of the manual linked above, which talks about all of these assemblers.

[faq10]: http://www.faqs.org/faqs/dec-faq/pdp8/section-10.html
[os8m]: https://archive.org/details/bitsavers_decpdp8os8_39414792
[os78m]: https://www.grc.com/pdp-8/docs/OS8_Handbook.pdf

    *   `DEVICE` and `FILENAME` alternatives to `TEXT` for passing arguments to OS/8 service routines
    *   `DTORG`: set DECtape block number in output for the [Typeset-8][ts8m] computerized typesetting system ([photo][ts8p])
    *   `IFNDEF` and `IFNZRO` negated forms of the conditional assembly tests
    *   `RELOC`: assemble code for relocation after loading

The restoration of the `FIXMRI` pseudo-op is curious. It is not clear from the manuals whether its use is again required for redefining memory reference instructions (MRI) after an `EXPUNGE` call or if it is merely for compatibility with certain existing PAL-III programs. (**TODO**: Try it and see.)

The existence of the `RELOC` pseudo-op should not be taken as a sign that PAL8 is a relocatable assembler. It simply allows code to be assembled starting at one fixed address which is intended to be run at a different fixed address. A proper relocatable assembler generally tries to hide the fixed addresses it uses when assembling your program; compare [SABR](#sabr), for example. You must give the generated binary code to a relocating loader to fix up the addresses to their final execution values.
The existence of the `RELOC` pseudo-op should not be taken as a sign that PAL8 is a relocatable assembler. It simply allows code to be assembled starting at one fixed address which is intended to be run at a different fixed address. A proper relocatable assembler generally tries to hide the fixed addresses it uses when assembling your program; compare [SABR](#sabr), for example, which produces output that cannot be run directly, but which must be processed by a relocating loader (`LOADER.SV`, in the case of SABR) to fix up the addresses to their final execution values.

PAL-III has one feature not implemented in PAL8:  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 information about undefined symbols out from among all the other output.

[ip]: http://bitsavers.org/pdf/dec/pdp8/handbooks/DEC-08-XINPA-A-D_intrPgm_75.pdf
[pl]: http://bitsavers.org/pdf/dec/pdp8/handbooks/programmingLanguages_May70.pdf
[ts8m]: http://bitsavers.org/pdf/dec/pdp8/typeset8/
[ts8p]: http://gordonbell.azurewebsites.net/digital/timeline/1968-3.htm