boot.coldplug is responsible for all devices that are not autodetected and for which no hotplug events are generated. It merely calls hwup for every static device configuration designated as /etc/sysconfig/hardware/hwcfg-static-*. This can also be used to initialize built-in devices in a different order than would be the case with hotplug, because coldplug is executed before hotplug.
boot.hotplug activates the processing of hotplug events. Because the boot parameter khelper_max=0 prevents the delivery of hotplug events in the early boot phase, the generated events are still in a queue in the kernel. The number of events that are issued concurrently is set by boot.hotplug in the file /etc/sysconfig/hotplug. In this way, no hotplug events are lost.