Memory mapped registers are still a thing today. Here's arm documentation describing memory mapped debug registers for Cortex-R chips: http://infocenter.arm.com

Memory mapped registers are still a thing today. Here's arm documentation describing memory mapped debug registers for Cortex-R chips: http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0460d/Cegejeeb.html http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.... Even the intel XAPIC (interrupt controller) has a mode which basically uses memory mapped registers for configuring interrupts. The trick with executing hot loops in registers definitely wouldn't work today, and in some microprocessors the merely reading registers can change the state of external devices.