Speaking of expensive screwups, one of the most expensive schematic errors ever was the routing of the interrupts on the original IBM PC. It put the serial inte

Speaking of expensive screwups, one of the most expensive schematic errors ever was the routing of the interrupts on the original IBM PC. It put the serial interrupt on the lowest-priority interrupt pin, instead of the highest. This spawned a trillion-dollar 'communications card' industry that was arguably not necessary. Certainly not necessary to the degree it grew. Interrupts should be prioritized by latency. Instead, the designer prioritized them by, I don't know, their most favorite to least favorite? E.g. the disk transfer completion interrupt was very high, even though it literally has infinite latency (nothing irrecoverable is going to happen if it's delayed indefinitely). If I had a time-travel machine that only allowed a 1 centimeter window into the past, I would open a window to that original schematic and swap the disk and comm interrupt lines. That would have changed silicon valley history.