A Turbo-Basic XL compiler created binary executables, further speeding up program performance to about ten times faster than Atari BASIC.

Turbo-Basic XL also includes an expanded editor, support for named procedures, WHILE...ENDWHILE and similar block constructs, and added access to the underlying hardware, which, among other things, allowed operation of attached floppy drives without exiting to DOS.

This version of BASIC had a number of custom commands that allowed partial access to the system's advanced features like graphics and sound.

It was notoriously slow, appearing at the very bottom of the list of microcomputer BASICs in the original version of David Ahl's Creative Computing benchmark.

In MS-derived BASICs the line numbers were stored as 16-bit integers and numeric constants in the code in their original ASCII format.

Atari BASIC worked differently, converting all numeric constants to a 6-byte floating-point format when the line was entered.

The other major source of poor performance in Atari BASIC was its very slow binary-coded decimal (BCD) floating point code.

The library, contained in a separate 2K ROM and considered part of the operating system as opposed to BASIC itself, had been written in a hurry and never optimized.

For programs that used math extensively, the new library resulted in dramatic performance improvements, sending the Atari from near the bottom of the Creative Computing Benchmark lists to near the top, beating a number of machines that were much faster in hardware.