We knew the memory read/write times for the different types of RAM in the system, as well as the machine language op code times for all the operations necessary to copy memory from one type of memory to another, with/without color-keyed transparency. The CD-I system provided triggers for when a given scan line was displayed, so with careful timing one could write code with the knowledge that there is time to perform some ambitious calculation. For example, to just copy a block of memory is one thing, but between different types of memory and the timings are different. Now add in the real world necessity of copy with color-key transparency, meaning you need to look into the memory you want to overwrite to choose if the overwrite is going to happen. That has a whole separate set of timings. Combine that with hybrid logic that figures out where dumb block copies and smarter color-key transparency timings trade off, and you have a process segmentation.