HLT is absolutely used in modern systems, ARMs have the WFI and WFE (wait for interrupt, etc). They're essential for dropping in to low power modes, though admi

HLT is absolutely used in modern systems, ARMs have the WFI and WFE (wait for interrupt, etc). They're essential for dropping in to low power modes, though admittedly HLT wasn't used for that back in the day.