1.  Field of the Invention
This invention relates to a navigation device that can display travel information.  The device finds particular application as an in-car navigation system. 
2.  Description of the Prior Art
GPS based navigation devices are well known and are widely employed as in-car navigation devices.  Reference may be made to the Navigator series software from the present assignee, TomTom B.V. (now TomTom International B.V.).  This is software that, when running on a PDA (such as a Compaq iPaq) connected to an external GPS receiver, enables a user to input to the PDA a start and destination address.  The software then calculates the best route between the two end-points and displays instructions on how to navigate that route.  By using the positional information derived from the GPS receiver, the software can determine at regular intervals the position of the PDA (typically mounted on the dashboard of a vehicle) and can display the current position of the vehicle on a map and display (and speak) appropriate navigation instructions (e.g. ‘turn left in 100 m’).  Graphics depicting the actions to be accomplished (e.g. a left arrow indicating a left turn ahead) can be displayed in a status bar and also be superimposed over the applicable junctions/turnings etc in the roads shown in the map itself. 
Reference may also be made to devices that integrate a GPS receiver into a computing device programmed with a map database and that can generate navigation instructions on a display.  These integrated devices are often mounted on or in the dashboard of a vehicle.  The term ‘navigation device’ refers to a device that enables a user to navigate to a pre-defined destination.  The device may have an internal system for receiving location data, such as a GPS receiver, or may merely be connectable to a receiver that can receive location data.  The device may be a portable device or may be built-into a vehicle. 
Conventional GPS based navigation devices (in common with other forms of embedded devices or systems) execute all the OS and applications code in place from a large mask ROM or XIP (execute in Place) Flash memory device.  There are several disadvantages to this: ROM based designs generally require the ROM to be burnt at an early stage in the manufacture of a product; once the ROM mask is fixed, altering it is costly and can be complex.  Hence, ROM based design are inherently inflexible.  Secondly, mask ROM and XIP Flash are costly.