Using Palm m50X Expansion Card > Multimedia Card vs. Secure Digital
A very common question on the message boards concerns the difference between SD and MMC as formats. Searching on-line at the time of this writing, a 64MB MMC card will cost between $80 and $100, before shipping. Secure Digital (SD) cards cost more, with current prices ranging between $90 and $250 (!). The question is, what do you get for the extra money when you purchase SD?
If you read the literature available on the web, you'll find that there are primarily 5 differences between the two: speed, durability, write-protection, copyright protection, and size.
Speed | ||||||||||||||||||
Maximum
transfer rates of SD are faster than that of MMC. SD has the capacity
of being 4 times as fast as MMC. Whereas MMC can transfer data at 2.5MB
per second, SD can transfer data up to 10MB per second. These are maximum
speeds and will depend on the device utilizing the card. The Palm does not
approach these speeds for tasks such as writing data to the card, but it
is possible to see a performance difference.
For each test, I repeated the action 5 times and took the average to minimize the variability associated by hand-timing the actions. The results, in seconds, were:
As you can see, the difference in speed will only make a significant difference when you move large files to and from RAM (particularly when you move a file into RAM). The transfer rate on the Palm, possibly due to its relatively slow processor, seems to achieve, at best, a 200kb per second transfer rate. The difference in speed for opening and closing applications with PowerRun or accessing files using MSMount is not perceivable (the differences shown in the table are probably not statistically significant). Summary: I would not let the advertised speed difference sway your decision on which card to buy unless they are very close in price. |
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Durability |
The thicker casing and, apparently, changes in the design of the cards means that the SD card is more durable and resistant to electrostatic discharge. Summary: I have heard no complaints about the durability of MMC and mine has worked without any problems. This does not seem to be a compelling reason to purchase SD, unless perhaps you live in a climate prone to static discharge. |
Write-protection |
SD includes a small switch on the side of the card that has two settings: Locked and Unlocked. If you set the card to the locked position, the Palm (and other devices) will not be able to write to the card, erase data from the card, etc. Summary: I must admit that I do not see this as particularly useful, but if you are concerned about important data being overwritten, this might be an appealing feature to you. |
Copyright Protection |
This is the most mysterious difference in the two media. According to the spec sheet provided by SanDisk (one of the consortium that developed the media), SD includes "cryptographic security for protection of copyrighted data." Presumably, this is to prevent people from copying information form a card (e.g., a card with games on it) and distributing it to other people. Unless you are planning to sell cards with data on them, this is of no direct benefit to the purchaser. It appears that this copyright protection may actually consume a several 100kb of space on the card - which you cannot get back. The amount of space lost on a card is higher for SD than for MMC, from what I can tell so far. Summary: Not a bonus for the consumer, and may actually be a problem. |
The Bottom Line | |||||||||||||||||||||||||||||
The bottom line is that you probably should not pay a premium to own SD instead of MMC. I personally would not purchase an SD card unless the cost difference were $10 or less.
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Some References |
You can read more about the SD format by viewing
the spec sheet provided by SandDisk. (You will need Adobe Acrobat to read
it.)
Palm's Knowledge base also can provide some information on the topic. |
Using Palm m50X Expansion Card > Multimedia Card vs. Secure Digital