So what is the largest size SD card anyone has used? I am using a 256mb card right now. I have a 1gb that I use on my PDA but I have not tried it yet.

4GB should be the limit

afaik there is no technical limit at all - but you might need to use several partitions on a card (which the software must support obviously)

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There is some kind of limit, at least when accessing the card in SPI mode as we do with MMC64. The SPI command to read something has a 32bit value for the byte address, this makes 4GB the limit as our guest already stated. Don't know about MMC mode...




I'm using a 1G card for some time now, and no probs. My 256M TwinMos was a bit more trouble as it does not ignore a command's checksum byte in non-crc mode, like the spec suggests.

There is no limit of the SD-Cards themselves but there is a limit of the FAT16 filesystem. To my knowledge, FAT16 can address a maximum of (nearly) 2 GB. If you want more, you are forced to use a different filesystem (FAT32 maybe).

FAT16 has ~ 2 GB limit (65524 * 32 kB clusters) according to Microsoft specification, but Microsoft broke it's own specs allowing 64 kB cluster size with Windows NT, bumping the limit to 4 GB. GB as used by card and HDD manufacturers is 10**9 bytes, so FAT16 limit is 2.1 GB if you ask them.

With large card sizes it will be better to use smallish FAT16 partition which MMC64 BIOS and Windows can see, and fill the rest of space with multiple FAT16 partitionsor use FAT32. That will cut down wasted space significally.

I have tested a cheap (can't remember brand and removed sticker) 2GB I have my games and some demo's on that one.. Works great !

I need to get another 2GB one so I can get the svs-trc Demos ftp on there.. (all unzipped ~ 1.3 Gb) and some more..

With different toolage.. The D64 writer is a lot more usefull than the D64 mounter for most demo's etc

Has anyone tried over 2GB SD cards..
Does the MMC64 allow 64 kB clusters ?
I also haven't checked the economics of 2 X2 GB SD's vs one 4GB yet.. But if I buy a 4GB, I'll report..

FYI, in addition to compatibility issues with FAT16, SD card readers conforming to the SD 1.0 specification can only address cards up to 2GB in size. SD 1.0 uses byte level addressing with a 31 bit quantity, whereas SD 2.0 uses the same interface, but uses sector level addressing. The MMC64 would need to support sector level addressing (SDHC or SD 2.0) in order to support 4GB or higher cards.

From my test with an A-Data 4GB card, the MMC64 w/BIOS 1.04 locks up on the insertion of a 4GB card. I have not tried reformating/partitioning the card to ensure filesystem incompatibilities are not responsible.

Really? Every spec I've seen shows address field as 32-bit entry. I've not paid either MMCA or SDA for official specs, tho


Your 4 GB card is likely FAT32, as FAT16 doesn't support >2 GB partitions without gludgery (64 KB clusters used in WinNT).

Interestingly, the various specifications say to send 32bits for SPI mode, but bit 31 is supposed to be 0, and they only define the media up to 2GB. I'm not entirely sure why, but I would suspect it has to do with the 1bit transfer mode, since that is the only required transfer mode in the MMC spec (SPI mode is optional).


Yes, and aside from the cost, the NDAs are excessive.


Indeed it was. I wasn't able to repartition my 4GB card from windows, and was not allowed any option other than FAT32 for formatting. However, I did partition it into two 2GB partitions on Linux, and put FAT16 filesystems on each. Even with this configuration, the MMC64 locked up on insertion of the 4GB card.

Windows is stupid, it doesn't allow partitioning removable media.

Did you try starting my browser first, then inserting the 4 GB card? I'd be interested to hear how it behaves. If it hangs you can use the built-in debugger to see MBR and PBR - keep C= down while inserting card, check if MBR is ok (browser assumes that first partition slot has valid entry: if $1c6-$1c8 of MBR is zero then it fails), then press C= + run/stop to attempt reading PBR.

I booted the mmc64 with my 1GB card in the slot, then loaded your browser off of that, removed the 1GB card, and inserted the 4GB card. Your browser worked fine, but only showed the first partition.

So it would appear that it's time for an updated version of the official MMC64 BIOS to give support for >2GB cards and/or multiple partitions... or better yet, FAT32 support. How hard can it be?

Fire away: http://rrforum.ath.cx/viewtopic.php?t=21

In fact, I'm a bit surprised why the MMC BIOS didn't come with FAT32 support in first hand. It shouldn't be that difficult.. I believe most of the hard work has been done already.

If Oliver Achten doesn't want to drop any current BIOS feature - quite hard. 8 KB isn't that big when features start to creep in.

Why was FAT16 supported instead of FAT32? Because size constraint and all available cards could be formatted with FAT16 when MMC64 was first done, I believe. Remember that minimum size for FAT32 partition is ~32 MB, and small cards were the cheapest ones back then. Not a big deal nowadays, I think, but changing file system now renders all plugins useless until they get patched.