To avoid the delays reloading the PE instructions would cause, the ILLIAC loaded the PEMs with the instructions on both sides of the branch. Logical tests did not change the PC, instead, they set "mode bits" that told the PE whether or not to run the next arithmetic instruction. To use this system, the program would be written so that one of the two possible instruction streams followed the test, and ended with an instruction to invert the bits. Code for the second branch would then follow, ending with an instruction to set all the bits to 1.