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RALF uses more or less the same statement syntax as the PAL family, but it is a very different assembler by nature. We can divide its differences into several groups.
#### Floating Point Processor Support
RALF is the back-end assembler for OS/8's FORTRAN IV compiler, which requires use of a Floating Point Processor (FPP) peripheral, and OS/8 FORTRAN IV delegates all of the FPP handling to RALF. Indeed, Vincent Slyngstad [suggests][smal8] that you think of RALF as an assembler for the FPP rather than for the PDP-8.
The first FPP peripheral from DEC 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. This is possible because the FPP 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 instruction-compatible with the FPP-12. The FPP features of RALF facilitate use of these peripherals in programs you write in those assembly languages.
The first FPP peripheral from DEC 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. This is possible because the FPP 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 instruction-compatible with the FPP-12. The FPP features of RALF allow you to intermix FPP instructions with PDP-8 instructions just as if the FPP were part of the PDP-8 CPU, rather than being a very different external coprocessor.
Here is a summary of the FPP-related features of RALF:
* More instructions and pseudo-ops:
* Arithmetic: `FADD`, `FADDM`, `FDIV`, `FLDA`, `FMUL`, `FMULM`, `FSTA`, `FSUB`
* Conditional jumps: `JEQ`, `JGE`, `JLE`, `JA`, `JNE`, `JGT`, `JAL`
* FPP to PDP-8 jumps: `JXN`, `TRAP3`, `TRAP4`
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