If you booted up an IBM PC without putting a boot disk in, it booted to a Microsoft BASIC prompt that was burned into the rom.
The way I accessed BASIC was to boot up PC-DOS (IBM-branded version of MS-DOS) and then run some program that was like QBASIC although it might not have been called that yet. Later I switched to MS-DOS 3.21, and that came with real QBASIC. I also switched from BASIC to Turbo Pascal and Turbo C. Great times!