There are two main reasons why there is a discrepancy between listed capacity of the memory card and what shows up on your computer. The most likely reason that your 512MB memory card shows up with only 485MB worth of capacity is due to the small discrepancies in algorithms and file formats by various operating systems. Also a portion of memory space is reserved for system files and data sectors for better memory card performance.
The second reason your card indicates less capacity on the device is due to capacity loss. When manufactured, some devices and card readers were not made to support higher capacity memory cards. An instance of this is 2 GB or higher capacity SD card that shows a memory capacity of 1 GB or less. It is always recommended that you research information on the device manufacturer to verify the correct supported format and capacity.
