43-44

The Zeropage addresses 43-44 ($2D₁₆-$2E₁₆), labelled TXTTAB contain the 16-bit address of the Start of BASIC Text.

The Start of BASIC Text is set to 2049 ($0801₁₆) as part of the BASIC ROM initialization routine. The address stored here may be changed from immediate mode. For instance if you wish to reserve some memory before the beginning of BASIC text for use in your program. But this state is only temporary and must be re-executed manually from immediate mode before the program is executed.

Variables are stored immediately after the end of BASIC text (VARTAB). Since BASIC text always ends with two zero (0) bytes, BASIC variables always start a minimum of two bytes after the start of BASIC text, even immediately after executing NEW.