From: Jens Arnold <arnold-j_at_t-online.de>
Date: Sat, 23 Aug 2008 08:07:31 +0200

>> I recently purchased a very cheap Archos Ondio and want to
>> get some extra memory for it. What is the maximum size
>> Multimedia card it can take?

> Definitely 2 GB is not the limit. We can use FAT32. The
> question rather is: what's the largest MMC you can buy?

> They're not as popular as SD, therefore lag behind. SD(HC) has

Standard SD has a limit of 2GB. SDHC is specified for up to 32GB.
The technical limit is much higher: SDHC uses block addressing
instead of byte addressing. Therefore it's also not backwards
compatible: an old SD card reader cannot read SDHC cards.

> an architecture limit of 16GB (I think, or was it 32?). It may
> not apply to MMC, but I doubt you can buy such as MMC.

For MMC, things are similar. MMC3.x (and older) and
MMC4.0/MMC4.1 use byte addressing, and are therefore limited to
4GB. MMC4.2 introduces block addressing, pushing the theoretical
limit to 2TB (iiuc).

As far as the Ondio is concerned, there are 2 modes of MMC
operation to consider:

When accessing the MMC slot via USB, the USB-MMC bridge chip
handles the card. Since it doesn't talk MMC4.2, the limit in
USB mode is 4GB, independent of the firmware.

In normal operation mode, the limit depends on the firmware.
Rockbox currently supports up to 4GB. MMC4.2 handling could be
added, if I can get hold of such a card. The original firmware
is limited to 1GB due to their limited blocksize handling.

All that said, 8GB MMCs were announced 2 years ago by Samsung
and Microdia, but are still not available.


Regards, Jens

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Received on 2008-08-23