measures when operating on internal battery power as a part of these measures the controller may choose particular memory units to which it will write data depending on the specific power consumption characteristics of these memory units the power saving measures may be facilitated by preparatory and backup action that the control takes when external power is connected as described further hereinbelow behavior of controller 28 in power saving mode may differ from one device to another for example digital cameras typically perform memory write operations while operating on battery power in this case the controller may choose memory units with low power consumption for writing images to memory on the other hand images are typically read out of the camera while the camera is connected to and receives power from a computer so that power saving is not a consideration during read by contrast files are generally written to a portable media player such as an mp3 player while the player is connected to and receives power from a computer in this case it is more important that the files be written to subsystem 22 in a way that will facilitate low power consumption upon reading from memory array 26 which is usually performed under battery power as noted above controller 28 may also have high throughput and high reliability modes of operation which are typically invoked by host processor 24 in response to application requirements typically these alternative modes require relatively high power consumption for example the high throughput mode may be invoked for.