fuzzkaizer

Some of my turn ons.

UFO (1970), “Ordeal”

To give a specific example, the Altair 8800 and Imsai 8080 display whatever is currently on the address bus, as well as what data is located at that address. Much of the time this will be the raw binary of the currently executing instruction, but when a memory fetch or write occurs, it will display the data at that address for the clock cycle it takes to complete. There’s a third set of lights that display whatever is on the CPU status lines, such as if the program is accessing an I/O device, or whether it’s reading or writing to memory. The Imsai also has a bonus set of lights that are specifically for programs to display anything they’d like, but unless you’re running a program you wrote yourself, they tend to go unused.

At any instance in time, the data on the front panel tends to be somewhat meaningless (after all, it’s usually changing faster than you could ever perceive), but if you’ve ever used one of those machines, you’ll quickly learn that different programs “look” certain ways, and it really is very easy to tell something is wrong based upon the pattern of the lights alone. As the bootstrap program starts, the LEDs have a distinctive (static) pattern as it waits for the byte of data. Any typo, however, and your program will usually overwrite itself, causing a brief flurry of activity, followed by a steady glow as the computer inevitably gets stuck in a loop.

However! Pretty soon into the hobbyist computer age, people realized you needed a teletype (or a terminal) to accomplish anything practical. And as ROM-based bootstrap solutions started to appear, the front panel was effectively replaced by monitor programs, which let you manually examine or edit bytes in memory, all from the comfort of a keyboard. Within the monitor, you could enter simple programs in machine code, or debug contents of memory. Or, since you now have ROM at your disposal, you can simply have your bootstrap program in non-volatile memory, automatically loading your totally-legit copy of Altair BASIC from paper tape or cassette.

It’s worth pointing out that all of this happened shortly after the introduction of the Altair and Imsai in 1975. In fact, I’m only aware of one other machine of the era that bothered to include a front panel; the majority were essentially large, featureless boxes that connected to your teletype and loaded from ROM instantly on power-up. And with the introduction of assemblers, BASIC, and commercial software, it became exceedingly rare for anyone to bother writing programs in machine code. The 1977 trinity certainly kicked-started the age of computers as appliances with their built-in keyboards and video output, but the front panel was already dead by the time they came around.

USS Enterprise Control Panel Lights and Buttons

💡“1960s Christmas lightbulb salesman case.” 🎄

“Mmm. Kelp nougat crunch.”

levitating display!