PiDP-8/I Software

### <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:

*   relocatable output code
*   easy access to the optional FPP-12 [floating-point processor][fpp12]
*   easy access to the floating-point processor (FPP) peripherals for the PDP-8 family

The RALF assembler has a mode switch that causes it to generate absolute-addressed code, as PAL8 does. In this mode, it is called FLAP.

The FPP modes are the key advantage of RALF/FLAP. Vincent Slyngstad [suggests][smal8] that you think of these as assemblers for the FPP rather than for the PDP-8.

Although the FPP-12 floating-point processor peripheral was introduced with the PDP-12, it is not restricted to the PDP-12: it also works with all of the other PDP-8 family computers contemporaneous with and preceding it, going back to the original PDP-8. This is because it is a bus peripheral rather than a feature of the CPU proper. There was also a follow-on peripheral for the PDP-8/a called the [FPP8-A][fpp8a], which is compatible with the FPP-12. The FPP features of RALF/FLAP facilitate use of these peripherals in programs you write in those assembly languages.
The original FPP peripheral was the [FPP-12][fpp12]. Although it was introduced with the PDP-12, it is not restricted to the PDP-12: it also works with all of the other PDP-8 family computers contemporaneous with and preceding it, going back to the original PDP-8, because it is a bus peripheral rather than a feature of the CPU proper. There was also a follow-on peripheral for the PDP-8/a called the [FPP8-A][fpp8a], which is compatible with the FPP-12. The FPP features of RALF/FLAP facilitate use of these peripherals in programs you write in those assembly languages.

**INCOMPLETE**

[fpp8a]: https://archive.org/details/bitsavers_decpdp8pdpUsersManDec76_996770
[fpp12]: https://archive.org/details/bitsavers_decpdp12DE_2606247