[PaulHoule]

Circa 1980 BASIC was the dominant language for micros because you could fit BASIC in a machine with 4k of RAM. Although you got 64k to play with pretty quickly (1983 or so) it still was a pain in the ass to implement compilers on many chips, especially the 6502, which had so few registers and addressing modes that you're likely to use virtual machine techniques, like Wozniak's SWEET 16 or the atrocious p-code machine that turned a generation of programmers away from PASCAL.

FORTH was an alternative language for small systems. From the viewpoint of a BASIC programmer in 1981 the obvious difference between BASIC and all the other languages which that you could write your own functions to add "words" to the language. FORTH, like Lisp, lets you not only write functions but create new control structures based on "words" having both a compile-time and run-time meaning.

FORTH's answer to line numbers in BASIC was that it provided direct access to blocks (usually 1024 bytes) on the disk with a screen editor (just about a screenful on a 40x25) You could type your code into blocks and later load them into the interpreter. Circa 1986 I wrote a FORTH for the TRS-80 Color Computer running the OS-9 operating system and instead of using blocks it had POSIX-style I/O functions.

FORTH was faster than BASIC and better for systems work, but BASIC was dominant. Probably the best way to use FORTH was to take advantage of it's flexibility to create a DSL that you write your applications in.