cause the computer to single-step, that is run a single instruction and stop until the programmer pressed a button to execute the next instruction. An address stop could be set to stop a running program when it attempted to execute an instruction or access data at a specified address. The contents of registers and memory would be displayed in the front-panel lights. The programmer could read and alter register contents, change program instructions or data in memory or force a branch to another section of code. When multiprogramming became the norm it was no longer acceptable to tie up an entire machine for debugging, except for special situations. Programs called debuggers were written which provided the programmer with the equivalent of the front-panel functions without requiring the entire machine. Entertainment For fun, bored programmers would create programs to display animated light shows. Front panels in the late 1960s and early 1970s were quite brightly colored. When bootstrap ROMs enabled computers to start themselves without operator intervention in the late 1970s and early 1980s, most computers were built without a front switch panel. High-powered calculators, such as the HP 9830 based on ROM, were among the first computers to do away with front panels, and operators. Huge banks of "blinkenlights" and "blowenfuzen" were featured on TV and movies as the popular image of the "computer" during the 1950s to 1970. (A Burroughs B205 was used as a Hollywood prop for many of these shows.) Example The following procedure would bootstrap a PDP-8 system from an RK05 moving-head magnetic disk: Ensure that the machine is halted by lowering and raising the Halt switch; the front panel "RUN" light should then be off. Set the 12 data switches to 0030 (Octal address 30), depress the Load Address ("ADDR LOAD") switch. The address lights will change to "0030". Set the switches to 6743, raise the Deposit switch. The data lights will show this instruction. Set the switches to 5031, raise the Deposit switch. The data lights will show this instruction. Set the switches to 0030 (Octal address 30), depress the Load Address switch. The address lights will change back to "0030". Depress the Clear switch. Depress the Continue switch. The "RUN" light will illuminate and the operating system on the disk will be bootstrapped. This process works by depositing a simple, two-instruction program in memory and executing it. The first instruction commands the disk