- Why did x86 support self-modifying code in the 80s and 90s? (stackexchange.com)
On the simplest microprocessors, self-modifying code is not a special problem. On an 8080, you can write just ahead of the instruction pointer, and a few clock cycles later, the instruction you just wrote, will be fetched and executed as though it had been there all along. But as pipelines and instruction cache are introduced, this becomes more problematic.