When you turn on the power, a capacitor keeps the 6502's reset line low for several milliseconds. This causes the processor to fetch the instruction pointer fro

When you turn on the power, a capacitor keeps the 6502's reset line low for several milliseconds. This causes the processor to fetch the instruction pointer from $FFFE, and execution proceeds from there. Modern PCs are a little more complicated. As a users, it seems to me like 20% of that complexity is necessary, such as to configure the DRAM (which definitely has to be done before running any user code.) The rest is all accidental complexity and compatibility with various legacy mistakes.