The aperiodic interrupts offered by the APIC timer are used by the [[Linux kernel]] [[tickless kernel]]
feature. This optional but default feature is new with 2.6.18. With itWhen enabled on a computer with an APIC timer, the kernel does not use the [[8253]] [[Programmableprogrammable Intervalinterval Timertimer]] for timekeeping.<ref>{{cite web|url=http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1005802|title=VMware Knowledge Base|website=kb.vmware.com}}</ref> A [[VMware]] document notes that "software does not have a reliable way to determine its frequency. Generally, the only way to determine the local APIC timer’s frequency is to measure it using the PIT or CMOS timer, which yields only an approximate result."<ref name="vmware">[http://www.vmware.com/files/pdf/Timekeeping-In-VirtualMachines.pdf Timekeeping in VMware Virtual Machines (for VMware vSphere 5.0, Workstation 8.0, Fusion 4.0)], page 8</ref>
