Acorn System BASIC

System BASIC

"This is a 4K byte program which interprets the popular BASIC programming language. Acorn's interpreter uses 32-bit integers to provide a numeric range of ±2,000,000,000, and has additional instructions specifically aimed for manipulating real machine addresses. The interpreter requires an Acorn Operating System for handling keyboard and VDU and can typically process 500 statements per second."

System BASIC occupies 4K bytes starting at $C000, typically for a System 2 it will be in a ROM/EPROM whereas for disk based systems (System 3/4/5) it will be loaded from floppy into RAM.

Here is a pdf of  the System BASIC Manual which has quite a lot in common with the Atom's 'Atomic Theory and Practice':


The Atom comes with BASIC as standard, the core is the same as System BASIC but is has a number of additional features:

Atom BASIC occupies 4K bytes starting at $C000 and an additional ~2K starting at $F000 (see note below)


I have produced a source code for Acorn BASIC in ca65 format, by changing a 'switch' it will assemble either the System or Atom variant:



Note: the Atom object code file produced by my ca65 source produces a single file, in an Atom a single 8K ROM holds both BASIC and COS and the address decoding arranges for it to appear in two separated address spaces at $C000 and $F000.  If you wish to program two separate EPROMs either load the appropriate part of the source file into the programmer or use the following split files:

For those with disc based Systems here is an .ssd image containing System BASIC together with the Floating Point (FP) and Online (ONLINE) Extensions:

BASIC requires 4K of RAM at $C000 and for the extensions a further 4K at $D000.


 To run BASIC type 'RUN BASIC'


To use the FP Extension precede that command with 'LOAD FP' (type e.g. FPRINT PI from BASIC to see if its working)

or to run the ONLINE Extension again precede the RUN BASIC command with 'LOAD ONLINE' (type e.g. CLI from BASIC to see if its working, it won't do anything but if the extension is not present you will get an error)


As the FP and Online Extensions occupy the same memory space you can only have one of them running.


Back to Software


Acorn Home Page