PiDP-8/I Software

> **Historical vignette:** Where the earlier PDP-8 assembler manuals refer to the new ASCII character constant feature, they actually either refer to "USA SCII" or to "ANSCII", those being the original names of [ASCII][ascii]: the United States of America Standard Code for Information Interchange; or the American National Standard Code for Information Interchange. You may also see "US-ASCII" in some places, being another way of writing "USA SCII".

[ascii]: https://en.wikipedia.org/wiki/ASCII


## <a id="pal-d"></a>PAL-D

| **Introduced** | 1967
| **Manual** | [PAL-D Disk Assembler Programmer's Reference Manual](https://archive.org/details/bitsavers_decpdp8sofProgRef_1907666)
| **Introduced** | April 1968
| **Manual** | [PDF, 1.9 MB](https://archive.org/details/bitsavers_decpdp8sofProgRef_1907666)
| **Delivery** | paper tape

PAL-D is a descendant of PAL-III, originally appearing as part of the [PDP-8 Disk Monitor System](https://en.wikipedia.org/wiki/4K_Disk_Monitor_System), one of OS/8's predecessors. It would later reappear under TSS/8.
PAL-D is a descendant of PAL-III, originally appearing as part of the PDP-8 Disk Monitor System, one of OS/8's predecessors. It would later reappear under TSS/8.

[Wikipedia claims][dms] that the first version of the Disk Monitor was published in late 1967, but the earliest PAL-D manual I've been able to find has April 1968 as the date of its first edition.

PAL-D came in two forms, the 4K and 8K versions, referring to the minimum amount of core memory each required. Note that the 4K version could assemble for larger machines; it has the `FIELD` pseudo-op, for example, which is of no use unless your assembled program would run in at least 8K of core.

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):

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.)

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

[cs33]: http://iclces.uk/articles/a_teletype_font.html
[dms]: https://en.wikipedia.org/wiki/4K_Disk_Monitor_System
[ds78]: https://en.wikipedia.org/wiki/DECstation#DECstation_78


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

| **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]
| **Manual** | [PDF, 38 MB][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 handbook; two of its many editions are 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 the OS/8 handbook. The 1974 edition is linked above. You may also find the later [OS/78 Handbook][os78m] from 1979 interesting for comparison purposes.

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.
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 below. 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


### <a id="pal8" name="pal-8"></a>PAL8

The earliest attestation to the PAL8 assembler I've been able to find is in the May 1970 printing of [Programming Languages][pl], the second in a two-volume set on programming PDP-8 family computers. (The first volume being [Introduction to Programming][ip].) On page 14-7 in the section on 8K PAL-D, it gives a Disk Monitor command for saving the in-core copy of 8K PAL-D as "PAL8". It is therefore unsurprising that the OS/8 version of PAL8 is morphologically more similar to [PAL-D](#pal-d) than to [PAL-III](#pal-iii).

The earliest reference to PAL8 as a named product of DEC is in the [PS/8 8K Programming System User's Guide][ps8ug] from October 1970, that product being the immediate predecessor of OS/8.

PAL8 understands the same basic language as PAL-D 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.
PAL8 understands the same basic language as PAL-D but 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 PAL8 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.

PAL8 has many features not present in 8K PAL-D:

*   output option for producing input to [CREF][os8m]
*   more operators in expressions:
    *    `^` 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)
*   the `FIXMRI` pseudo-op is back
*   `EJECT` pseudo-op extended to allow the page header to be changed for the next and following pages
*   new pseudo-operations:
    *   `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, 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.
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`) 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
[ps8ug]: https://archive.org/details/bitsavers_decpdp8sofogrammingSystemUsersGuide_2417347
[ts8m]: http://bitsavers.org/pdf/dec/pdp8/typeset8/
[ts8p]: http://gordonbell.azurewebsites.net/digital/timeline/1968-3.htm


### <a id="ralf" name="flap"></a>RALF/FLAP

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