It looks like the person with the n900 tested the 64gb card as a usb device with the n900 in usb host mode. The n900 only has a microsdhc slot so there is no way to insert a full sized sd/sdhc/sdxc card in the slot. The nice thing about the n800 is it has TWO full sized slots, making 256gb possible using 128gb cards. Today that would be pretty expensive but that situation will surely improve.

Exfat is apparently patented but Linux native file system are better anyway.

Apparently the current generation sdxc cards (SD3.0) are electrically compatible with sdhc but the next generation will be incompatible (higher clock speed among other things).

I'll preface this by saying I'm far from an expert in the field, but as far as I can tell there should be no issue having SDXC cards recognised by the N800 assuming they're formatted to a compatible filesystem (and they can be formatted to FAT32 [if you use Windows like myself] with a bit of messing around).

I've almost convinced myself enough to buy an N800 and a 128GB card, because the utility would be beyond fantastic. If I do, I'll report back with confirmation.

Good question. I tried a 64 GB SDXC (Transcend) in my N800. The N800 complains that the card is corrupted but won't format it. I think that the answer to the question is no.

Do the same card work in a non-SDXC reader on a computer?

That question is difficult to answer.

I tried on a mac with various SDHC readers. Sometimes it works, sometimes it doesn't. When it does not work, the mac complains that the file system is damaged but can read at least part of the files nevertheless.

The mac has a built-in SDHC reader which predates the SDXC specification, but the cards can be read just fine in that reader. The card can also be read in an even older reader from Transcend (manufacturer of the card).

So it seems that SDXC cards are electrically compatible, but that some new software or firmware would be needed to make the N800 able to read them.

Disappointing, but I choose to remain hopeful. Would make the N800 have a very bright future as one's PMP.

I have the Sandisk Ultra SDXC 64 GB card, and once reformatted it works fine in my n800, I formatted it fat32 and the whole 64 GB shows up in n800.

The only issue I had was on my desktop, with the first usb SD card reader from Adata(which I used because it was out), this reader wouldn't see the card as anything other than 32 GB in gparted or windows. I then used my older Sabrent reader which worked fine. Not sure what was up with the adata reader.

Card readers need frequent updates; i.e. you'll have to purchase newer ones for newer cards (and probably experiment).

Well well, that may well make mirroring the firmware to a SD partition more interesting.

Shows that the N800 may actually have a longer usage life than first expected. Perhaps i should just get myself some SDXC cards and clone the firmware onto the internal one. And maybe also start looking around for a new battery.

Edit: after looking at Norwegian prices i think i'll rather go with a couple of 32GB SDHC. This in particular as the SDXC will not be any faster at the transfer rates. Still, with a new battery and a 32GB drive for the firmware and programs this may have a long lease on life still.

Indeed, I can't think of many other handhelds (let alone 5 year old ones!) that can be upgraded to 256GB internal storage today.

How about a (smaller, pricier per byte and harder to find but much faster and longer lasting) SLC for the OS & apps and an as-large-as-you-can-afford MLC SDHC/SDXC for media etc mass storage?