iMac SMC Firmware Update 1.1
This update is recommended for iMac (late 2013) with flash-only storage. This update improves the Power Nap feature in Mavericks on your flash based iMac by allowing it to perform silently, without spinning up the fan.
Power Nap periodically updates apps, such as Mail, Contacts, and Calendar, and will download software updates while your iMac is sleeping.