A ducted system works in the same way as a split system in that an outdoor unit is connected to an indoor unit. The difference is that the indoor component of the ducted system is placed inside the ceiling space, and the air flow is directed into each room via large insulated duct pipes. Ducted units are designed to provide cooling throughout the home.
Modern ducted air conditioning often allows for 'zone cooling' - that is, providing cooling to specific parts of the home as and when it's needed, without necessarily cooling the entire house. Reverse cycle ducted units have the added advantage of being able to provide heating as well.
Ducted airconditioning vs. split system
Ducted units are considerably more expensive to purchase and install than traditional wall-hung split systems, not least of all because they are designed to cater for a considerably higher output. They also use more electricity, even in their most economical modes.
The obvious advantage of a ducted unit is that you can use a single system to cool an entire house, although if you are considering one you should also evaluate how much of your house needs to be cooled (this is measured in terms of 'heat load'), and whether or not ducting is the most economical way to ensure comfort when and where you need it.
Calculating the requirements for ducted air conditioning in your house isn't as simple as doing a few sums - there are many variables involved with installing ducted air conditioning for multiple rooms. To get a better idea of what it might cost to adequately and appropriately cool your home with ducted air conditioning you should always consult a qualified installer.