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## <a id="pal-iii" name="pal3"></a>PAL-III
| **Introduced** | 1965
| **Manual** | [PDF, 790 kB](http://www.telegraphics.com.au/doc/paliii.pdf)
| **Delivery** | paper tape
We may presume from the name that PAL-III has two predecessors. I was able to find a reference to DEC product number 5-1-S, the Program Assembly Language for the PDP-5, which the PDP-8 directly replaced in DEC's product line, being upward compatible with it. That same [PDP-5 program catalog][pc5] says that its replacement is [an early version of PAL-III][p83s]. I have not been able to find a reference to PAL-II. Perhaps it went the way of Angular 3, Winamp 4, Netscape 5, PHP 6, MySQL 7, QuickTime 8, and Windows 9.
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 tape required at least two passes through the tape reader in order to produce a computer-readable BIN format output tape, plus an optional third pass if you wanted a human-readable listing on the terminal.
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 surveyed here share its basic syntax.
We will not list the feature set of PAL-III here; see its manual for that. The lists of features in the sections below are relative to either PAL-III or one of the other assemblers reviewed below. Within the PAL genealogical line, compatibility with the baseline PAL-III syntax is assumed unless a note is made otherwise.
[pc5]: http://bitsavers.org/pdf/dec/pdp5/PDP-5_pgmLibr_1964.pdf
[p83s]: http://www.ricomputermuseum.org/Home/equipment/pdp-8s/pdp-8-software
## <a id="macro-8"></a>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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| **Manual** | [PAL-D Disk Assembler Programmer's Reference Manual](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 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.
The 4K version defines only one new feature in the PDP-8 assembler family so far: the `XLIST` pseudo-op, which lets the programmer stop and then re-start the assembly listing in the optional third pass. The 4K version is more notable for the features it brought into the PAL family from [MACRO-8](#macro-8): the`PAGE` and `TEXT` pseudo-ops.
The 4K version defines only one new feature in the PDP-8 assembler family so far: the `XLIST` pseudo-op, which lets the programmer stop and then re-start the assembly listing in the optional third pass. The 4K version is more notable for the features it brought into the PAL family from [MACRO-8](#macro-8): the `PAGE` and `TEXT` pseudo-ops.
8K PAL-D added quite a few new features over the 4K version:
* ability to run in 8K or 12K of core, allowing assembly of larger programs
* automatic link generation for off-page references
* 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`
* more pseudo-operations:
* `EJECT`: emit a form feed in the listing output
* `IFDEF` and `IFZERO`: conditional assembly tests, affected statements in angle brackets
* `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 that the negated forms of the conditional assembly operations did not appear until later. The first reference to them I've been able to find for `IFNZRO` and `IFNDEF` is in connection with [PAL8](#pal8).
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 still find it documented in the [the OS/8 Handbook (1974 ed.)][os8m], but it was airbrushed out of history by the [1979 edition for OS/78][os78m], suggesting that its purpose became effectively redundant after the bulk of the market moved to disk-based PDP-8 systems.
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.)
| **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. 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
### <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 volume in a set of two books for programming PDP-8 family computers. 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 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).
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.
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:
* automatic link generation for off-page references
* output options for [CREF and DDT][os8m]
* in addition to `+` and `-` in expressions, it allows:
* `!` for Boolean OR (the ASR-33 terminal character set [did not include the ¦ character](http://iclces.uk/articles/a_teletype_font.html))
* `&` for Boolean AND
* single-character ASCII constants: `"A`
* 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. You must give the generated binary code to a relocating loader 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
### <a id="ralf" name="flap"></a>RALF/FLAP
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