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VARTOP is an internal BASIC variable giving the first free address after the BASIC heap. The heap's size is given by VARTOP-LOMEM.

When the next variable is defined or the next array or memory block is declared, it will be put at this address and VARTOP will increase by the size of the object. VARTOP's current value can be obtained non-destructively with:

DIM A% -1

which places the value in A%.

Unofficially, 6502 BASIC stores VARTOP in a word at address &0002.

-- beardo 14:13, 20 March 2007 (UTC)