Aus,
Why not make the RAM non-volatile? It would eliminate the need for a back-up power source altogether.
That is, of course, what makes MP3 players so cool. But there are a couple of problems with using flash like DRAM. The first obvious one is that flash memory is still very slow compared to DRAM. For things like phone lists, to-do lists, etc, it certainly seems reasonable to store them in flash since they don't change frequently and storage speed is not an issue, but your applications don't know that. To have reasonable performance, the application would need to run everything in DRAM until you said "save" and then save that list to Flash, loading it into DRAM next when you 'reboot' your PDA. This seems plausibly done, but it isn't the way software works now? I'm sure there are techniques to make this somewhat transparent (i.e. buffering the data in DRAM and then writing to flash in the background), but you'd still need some DRAM around to handle things.
The second more important but less discussed issue is that flash isn't perfect. Flash actually wears out on the order of 100k+ write-erase cycles (stops being programmable), so you can't use it like DRAM, where a cell (technically) could easily get written 100k times for an un-flash-friendly OS (lets say the OS saves some sort of status information in the same location in memory all the time).
I'd say those are the two mechanisms preventing flash from replacing DRAM. Considering the microprocessor and front-side bus speeds keep increasing, I don't see the situation improving for Flash. It would take some clever circuitry AND some clever software writing to make a high performance flash/DRAM mix.
Wouldn't it be great, though, to have the main chunk of your most used applications stored in Flash? Then you'd just click on 'em and WHAM, the majority of the program would already be in memory. It'd just have to access (from disk) the various option files and the data file you wanted. To me, that's very reasonable, since you don't change your core applications that often (similar to the WinCE being on ROM). . .And it could use lots and lots of Flash. :) However, in that case, it needn't be compact flash, as you don't need removable memory. Hmmmmmmmmmmm.
Steve |
