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BASIC III, the release supplied with the BBC B+, was produced in both a UK version and a [[United States|U.S.]] market version for Acorn's abortive attempt to enter the cross Atlantic computer market. Apart from a few bug fixes the only change from BASIC II was that the <code>COLOUR</code> command could also be spelled <code>COLOR</code>: regardless of which was input, the UK version always listed it as <code>COLOUR</code>, the US version as <code>COLOR</code>. This was the only difference between the two versions.
BASIC IV, also known as CMOS BASIC, available on the [[BBC Master]] and BBC Master Compact machines, was changed to use the new intructions available in the 65C12 processor, reducing the size of the code and therefore allowing the inclusion of <code>LIST IF</code>, <code>EXT#</code> as a statement, <code>EDIT</code>, <code>TIME$</code>, <code>ON PROC</code>, | in <code>VDU</code> statements and faster floating point. Bug fixes were again included.
With the move to the 32 bit [[ARM_architecture|ARM]] CPU and the removal of the 16kB limit on the BASIC code size many new features were added. BASIC V version 1.04 was 61kB long and included many new commands such as <code>WHILE-ENDWHILE</code>, <code>IF-THEN-ELSE-ENDIF</code>, <code>CASE-OF-WHEN-OTHERWISE-ENDCASE</code>, <code>RETURN</code> parameters in proceduces, local arrays, procedure libraries (<code>LIBRARY</code>, <code>INSTALL</code> and <code>OVERLAY</code>), <code>LOCAL DATA</code> and <code>LOCAL ERROR</code> handlers, a relative <code>RESTORE</code>, array operations, new operators, <code>TRACE STEP</code>, along with commands for the new sound system, mouse, graphics. The graphics commands were entirely backwards compatible, the sound less so (for example, the <code>ENVELOPE</code> keyword from BASIC V onwards is a command which takes fourteen numeric parameters and does nothing.) The in-line in 6502 assembler was replaced by an [[ARM_architecture|ARM]] assembler. BASIC V was said, by Acorn, to be "certainly the fastest interpreted BASIC in the world" and "probably the most powerful BASIC found on any computer".
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