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Secure Digital vs. Multimedia Cards
n1ywb asks: "I recently cajoled myself into buying a Dell Axim. Since the compact flash slot is obviously taken up by my 802.11b card, that leaves me with the OTHER slot for adding additional storage. This other slot is billed as a 'Secure Digital Card' slot, although I understand it is backwards compatable with the 'Multimedia Card' standard.
The name 'Secure Digital' is somewhat misleading it seems. It has some kind of digital rights management technology onboard, which nobody seems to want to elaborate on. It has hardware encryption, which sandisk.com touts as 'Cryptographic security for copyrighted data based on proven security concepts from DVD audio.' Hah! DeCSS anyone? Magic markers?
There isn't a lot of REAL information about SD cards out there. I like cheap and fast storage, but I'm paranoid of DRM. _I_ am god here; my hardware is slave to me. I don't want my PDA telling me I can't play my Grateful Dead bootlegs because they aren't digitally signed. Should I buy MMC or SD? Where can I find more info? Any real world experiences? What do you think is the bottom line?"
SD does have some real technical advantages over MMC. It is much faster, up to 10 megabytes per second. The cards have a physical write protect switch, and they have a very high ESD tolerance of +/- 10K volts for contact discharge and +/- 15K volts for air discharge. They also seem to be slightly cheaper now."
"Here are a couple of other choice quotes from the Sandisk page:
'...included are unique and proprietary security features implemented within the card's controller which facilitate the secure exchange of content between host devices and the card.'I read somewhere (trying to find the link) that the DRM technology in the card consists of a chip similar to what would be found in smart cards. It can limit, for example, the number of times a file can be copied off the card.
'The SD Card is designed to comply with all three levels of SDMI security requirements. Both non-protected (category 1) and copy protected (categories 2 & 3) material can be stored on the card. The copy protected material can be secured either by a unique card bound identification (category 2) or by an active cryptography algorithm (category 3), that involves challenge/response protocols against a private key. The SD Card security features also have the capability to revoke non-compliant SDMI components using a Media Key Block if security is breached. Under this security scheme, a content provider's data (music, books, software applications, maps, schedules, etc.) can be Checked-In (moved to the card), Checked-Out (moved from the card) or copied to other SDMI compliant cards with necessary copy restriction. The Check-In/Check-Out feature gives the content owners the confidence that their content is protected.'
SD does have some real technical advantages over MMC. It is much faster, up to 10 megabytes per second. The cards have a physical write protect switch, and they have a very high ESD tolerance of +/- 10K volts for contact discharge and +/- 15K volts for air discharge. They also seem to be slightly cheaper now."
SD is used by certain hardware mp3 players as part of the DRM stuff. My girlfriend's Panasonic player uses SD and a specially modified copy of Realjukebox to send files to the card. If you're not using it for "secure" stuff, it just acts like an ordinary MMC card. I've mounted it in a card reader under Linux to download digital camera photos, and used it as a handy way to transfer files. There's no problem with it at all.
You can use SD for both, but it tends to be a little more expensive (presumably because of the crypto deelie). At least, that's in my experience, using Windows 98 and Linux. Your mileage may vary, especially if you're using a newer version of Windows.
SD is faster (4x?) than MMC, in theory. But make sure the slot in your device can take advantage of that -- the Zarus SL-5x00 cannot.
Some devices only support memory (not SD accessories like bluetooth).
Stranger still, some support only MMC. The Franklin e-Bookman (a palm-class device recently on sale for $50 at costco!) manual claims to support only MMC. (and an aside, the MMC storage in the e-Bookman is not general purpose -- only certain types of data can be put on the card rather than RAM)
For whatever reason, some devices support a limited range of flash sizes. The e-Bookman is limited to 64M. The Zaurus requires a software upgrade to use 256M cards.
And finally, make sure you can easily return/exchange your card. The Zaurus, for example, can mount and read any brand of card. But a problem (driver bug? hardware bug? card bug?) causes some to become inaccessible after a suspend/resume event. You can find tables of user-tested cards online, but I wouldn't necessarily risk postage or a restocking fee on their accuracy.
I've got 3 different devices with SD/MMC support: my Palm m505, Compaq iPAQ PA-2 MP3 player, and a Minolta DiMAGE X camera.
The DRM capabilities are for companies who are providing data preinstalled on the card, and not for how you wish to use them -- as flash (although you could turn it on if you so chose, how? I'm not sure). For instance, Palm sells SD cards with preinstalled software (Atlases, games, etc.). You can't copy them off the card and install them in your Palm without some other intervention.
MMC is a bit more pervasive, so if I was thinking about investing in the media, I'd buy MMC. Most devices don't support the full transfer speed of SD, SD cards are physically thicker than MMC cards, so SD cards don't work in as many devices (i.e. my SD card I got with my camera won't work in my PA-2 because it's too thick). And heck, MMC cards are typically $20 to $40 cheaper too (if you've found them cheaper, pass it along!).
But then again, to each his own, right?
SD can be considered sort of the `CardBus equivalent for MMC' -- it's a faster data connection in the same connector footprint. My understanding is that SD cards can be roughly 4x faster than MMC. Additionally, there are a number of non-memory devices that only come in SD format (most interestingly, the SD BlueTooth card).
Unfortunately, SD is a highly propietary format, controlled by a standards consortium that charges very high entrance fees, and heavily restricts the ability of members to distribute information about the format. This is why, for example, the Sharp Zaurus uses a proprietary, closed driver for its SD slot, and why the various Linux-on-iPaq systems (http://www.handhelds.org/) do not have SD support (unless the license/consortium radically changes, there won't be an open driver for this format).
SD/MMC is a nice, convienent format. In its size/power category, it's more functional than SmartCard, which is memory only. The next best competitor is probably MemoryStick, also a very, very closed system. SD/MMC also has the `feature' that it's commonly found on Palm, PocketPC, and Linux handhelds. It's a shame that open systems will be stuck using only the MMC feature set of these systems.
I'm, for my sins, a moderator over at the Palm discussion forums on www.brighthand.com.
Our experience on the board is that while the SD cards are theoretically faster than MMC, the speed difference is not very noticeable, and in fact differences between manufacturers seem to account for as much variation.
However, this may be a hardware issue with Palm handhelds as the new super-fast Tungsten T seems able to access cards a lot faster, and some people are now reporting SD cards as faster than MMC.
For my self, I have used both in my M505 and found almost no difference in speed, so from now on I would go for MMC as it is fast enough and so much cheaper.
~~~~~ BigLig2? You mean there's another one of me?
There is NO /Free Software/ SD Card driver for Linux, just MMC.
Sharp uses proprietary binary drivers in the Zaurus.
From http://www.handhelds.org/projects/h3800.html
Why do MMC cards work, but SD cards don't?
The SD Card Association product license agreement does not allow open source drivers for the SD cards. The Multimedia Card Association (which came before SD) does allow open source drivers.
Can't someone release a binary-only SD card driver? We could. We don't for the following reasons: (1) it's a maintenance headache. Someone must compile and update the driver for each kernel release. (2) People who want to hack a custom kernel will not be able to include SD card support unless they join the SD Card Association. (3) It goes against the grain of open-source operating systems and the whole point of handhelds.org. Driver development work is replicated, bugs go unfixed, time is wasted.
We will continue our efforts to change the SD Card Association's policies.
So, MMC is definitely better in this regard.
BTW, the MMC card reader that came with my RCA CC-9390 DVC camcorder works under Linux with the standard USB drivers. It talks SCSI over USB and then the card has a x86 boot sector and partition table indicating a FAT filesystem. It all works. I was quite surprised and impressed.
I don't know if a SD card reader would work under Linux due to all the DRM crapola.
Using your sig line to advertise for friends is lame.
As far as I understand it MMC uses a SPI like signalling up to 20MHz, SD uses the same (with more options) the x4 speed comes from offering 4 data lines so can be nibble parallel rather than serial, thus 4 times the data but few devices have bothered to suport this high speed mode SPI protocol issues may limit this anyway. The MMC spec is fully relased and available to anyone the SD spec is available to SD CARD group memebers only, so not a lot is known about the "extra features". MMC is fine for everything, but my experince has been, different from other posters, that SD with the extra feature is actually cheaper than MMC. As an end user with a PDA there will be no difference buy which ever is cheaper, your application software must enable the security features so nothing is going to happen without your control and should only be an issue in a MP3 player that offers DRM, Sony uses this in their Magic Stick (White ones) that are replacing the Memory Stick (Purple ones), but most evryone else is ingnoring this.
As it turns out, MMCs have a lower price per megabyte in 16, 32, and 64 meg capacities. As capacities go up, the gap closes however, and at 128MB SD overcomes MMC as the cheaper of the two. Appearantly only SD is available in 256MB and 512MB capacities.
Sorry but this is the best I can make my table look, since /. doesn't allow tables in posts.
-73, de n1ywb
www.n1ywb.com