Originally Posted by moffattm
That is exactly what I thought too when the idea of the size of the book's cache affecting battery life came up. Surely the whole memory is being kept alive by the battery when the device is in sleep mode, not just the portion of memory being used. It would be way too hard to figure out which parts of the memory are being used and to power just those parts (even if it was possible to power individual memory chips, and is there even more than one memory chip in the Kobo's?) Also, stuff normally isn't necessarily stored in a contiguous chunk of memory, it's common to have stuff all over the place as chunks of memory are allocated and freed by the OS.
Note I'm looking at this from a programmers perspective, I don't know all that much about the actual Kobo hardware.
Kobo uses Freestyle processors in the devices, and these processors are basically system-on-a-chips, which means that the CPU and the memory are on the same chip.
The chip may be smart enough to be able to turn off portions of memory that aren't being used, but there isn't that much memory, and stuff tends to get written to semi-random memory locations, so I'd say that all of memory is either on or off.
During sleep mode, memory will be in a sleep mode, where only enough power to refesh it is consumed. When the appropriate hardware trigger (power button toggle) happens, then the processor and memory are awakened, and the device is back in business.