X86 timing
- PIT -- Programmable Interval Timer (eg Intel 8253)
- ACPI counter
- LAPIC counter
- HPET
- TSC since Pentium
- RTC (Linux docs)
- ACPI standardized the cmos-rtc type, extending the Motorola MC146818 (CONFIG_RTC_DRV_CMOS at the LKDD)
- Linux clocksources vs clockevents