Inspired by this thread:
http://www.aximsite.com/boards/showthread.php?t=76407
Cliffs Notes Version:
X50/X30: Program Memory=RAM=For running programs
Storage Memory=RAM=For storage
Built-in Storage=ROM(flash)=For storage
X51: Program Memory=RAM=For running programs
Storage Memory=ROM(flash)=BIS=For storage
This topic has been discussed in various threads all over this site and others, but several members have asked for a “memory help for noobs” that is specific for the X51 series Axims. So here he we go…
The X51 was developed in order to take advantage of the Windows Mobile 5 operating system. One of the developments of WM5 was the use of persistent storage. This means that your data doesn’t disappear when you run out of power. In a sense the memory system of an X51 is probably more familiar to most people because it works much like that of a desktop or laptop computer. Your programs and data are stored in the “Storage Memory” which is actually a non-volatile flash memory (referred to confusingly as ROM or flash ROM). This is analogous to the hard drive of a desktop computer and equivalent to the “Built in Storage (BIS)” of the X50. When you boot up the Axim and start to run programs, they are loaded into the “Program Memory” which is volatile RAM. This is exactly like the RAM in your desktop. RAM requires essentially constant power in order to maintain data. This is why you lose whatever you are working on when your computer crashes, but if you had saved recently (to the hard drive for example) the data is still there.
The X51 also has the ability to use removable Secure Digital (SD) cards and Compact Flash (CF) cards. These are non-volatile flash memory just like your “Storage Memory.”
For users, the memory system of the X51 is actually simpler than the X50. When you install an application you only have the choice of installing to the “Device” or to a memory card (if present). Installing to the “Device” means installing to the “Storage Memory.”
This wouldn’t be so confusing if they would have just renamed “Storage Memory” to “Storage” and “Program Memory” to “Memory.”
So if RAM requires power, why don’t we just use only flash memory?
The main reasons are it is much slower than RAM, and that flash memory has a limited number of write cycles before it craps out. With the x50, you could use some of the RAM for storage (“Main Memory”), and you could use a slider bar to decide how much to allocate for storage and how much for program memory. WM5 does not constantly power the RAM, so storing programs or data here would result in loss every time you had to reset, turn off the device, or run the battery dry. So, there is no slider to allocate RAM in WM5 and it’s not used for storage.
Dell said my Axim comes with 64 Mb of RAM (SDRAM for the geeks), but the memory app in WM5 says I only have ~50 Mb. Dell ripped me off!
Don’t start a class action suit just yet. Your Axim has 64 Mb of RAM but only about 50 Mb are available for use. The rest of it was allocated for various buffers that are needed by WM5 and whatever apps Dell decided were critical. Essentially they just told the OS there is only 50 Mb of RAM so it wouldn’t try to use the rest.
Ok. But I haven’t installed anything and I just did a hard reset/ soft reset and I still don’t have 50 Mb of “free” RAM.
Yup. The WM5 operating system is using some of that as well as any programs you have set to load on startup and any today plugins. There are probably a bunch of other running programs that are necessary to run your hardware that are transparent. You can free up RAM by removing today plugins and startup apps and by using some of the memory reclaiming programs out there (like MeMaid, FreeUpRam, etc.) but there is not much you can do about what the OS is using (without some hacking I guess). You only get about 30 Mb to play with. I wouldn’t worry about it unless you are running out of RAM or just really like that kind of thing.
RAM, shmam. Where do I install all my stuff? Storage memory or flash cards (SD/CF)?
This is somewhat of a personal choice. Remember that flash memory can withstand a limited number of write cycles so eventually it will die. This has led some people to try to move everything that gets written to often (like the browser cache) onto cards. The card will eventually die too, but it’s much easier to replace than the internal Storage Memory. Some programs claim they must be stored on the Device to function correctly. Some users have found no problems when moving them to storage cards. It’s probably a good idea to install things that you want to run at startup onto the Device. I generally install system utilities (like Total Commander, etc.) and PIM stuff (like Pocket Informant, etc.) onto the Device. This assures that they are always available regardless of which cards I have installed. I install games, movies, music, fun stuff, etc. onto SD cards, which I swap out often. I use SD cards for this mostly because they are easier to lug around and easier to remove. I generally store data, office-type files, maps, backups, and some apps on my CF card which I rarely remove (I’ve only got one).
Wait. You said I couldn’t install things to RAM on an X51, but Menneisyys says I can using a RAMDisk, and he’s a real computer scientist who is smarter than you and can leap tall buildings in a single bound.
http://www.aximsite.com/boards/showt...hlight=ramdisk
Yes, this is all true (he can also sync and charge his Axim with his mind). However, the RAMDisk doesn’t change the fact that the X51 doesn’t constantly power the RAM, so the RAMDisk will be wiped clean during any soft reset, full power off or loss of battery power. Don’t come crying to me. You were warned.
I hope this is useful for someone besides me (see now I can just paste a link instead of re-explaining all of this). Comments, criticisms, condemnation, corrections, commendation, congratulations, compensation, and other c-words can be sent by PM or just put them down there.
mm
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I'm not sure I can answer that satisfactorily. (Compaction threads and NAND vs. NOR.) Maybe a real computer scientists would like to take this one. (But, maybe not in the newbie forum ;)). 
