Obscure facts ...

On the Sinclair computers (incredibly popular in the UK, the BASIC was not written by Microsoft) it was in fact possible to predict where the program would be loaded, so a very popular place to store machine code was in a REM statement. This also had the advantage that you could save the machine code by saving the BASIC program.

On the ZX81, the first byte of the payload of a REM statement at the beginning of the program was at address 16514, hence:

  RAND USR 16514

was the command to run the machine code. (RAND set the random number seed and was just used as a convenient way to turn the USR function into a BASIC statement. The contents of the BC register were the return value from USR).