The SD standard only allows for cards up to 2GB due to the use of 32-bit byte addressing. SDHC expands the capacity to a theoretical maximum of 2TB* through the use of sector addressing instead of byte addressing. Before SDHC was introduced, some manufacturers increased the capacity of their cards to 4GB by using a control bit, normally used for parity information, as an additional address bit (essentially extending it to a 33-bit address). Since these cards effectively removed the parity control bit, they are less reliable than standard cards, are not compatible with many devices, and technically don't even meet the SD technical specs set out by the SD Card Association. Many companies still sell 4GB non-SDHC cards, but I would avoid them at all costs. * (When can I expect these to come out?...I'm practically drooling at just the thought of 4TB of storage in an N800!) (Then again...since a single memory card would probably cost 10x as much as the N800, it might not be very practical.)