Secure Digital (SD) media has found wide acceptance due to its size and the preferred format for Palm and PocketPC handhelds. (Sony was pretty much the only manufacturer trying to push a proprietary format -- the memory stick.) Anyway, SmartPhones need memory too and sometimes more than what's already included (mostly for data and backups etc.). So it happened that my palmOne Treo 600 needed a little memory infusion and since I had good results with the Sandisk's 512MB Ultra-II Compact Flash card, I chose to try their 256MB SD Ultra-II card as well (after getting an 'emergency' standard card with 128MB).

Anyway, $29 for Sandidsk's SD 256MB Ultra-II was a good reason to try it for my palmOne Treo 600. Especially since SD cards are normally more expensive.


PERFORMANCE

Capacity: As noted before, Sandisk is not the only manufacturer that plays the numbers game and usable memory is actually less than the claimed 256MByte. The tested card claimed a sized of 241MB (253.xxx.xxx Byte) and that's close enough to 256 million bytes. However, it's still no 256 MegaBytes.

Speed: Speed rating for flash memory is one thing and usually only high speed cards are listed regarding their rated data transfer. The Ultra II is supposed to be good for 9MB/s writen and 10MB/s read, but can the device use that to its advantage? VFSMark is a benchmark program that tries to answer this question by comparing it relative to a Palm m500 with a 16MB SD card (no speed rating). While this doesn't mean much, it still allows to compare speeds between different devices and external memory. (Higher numbers are better.)

Note: VFSMark results seem a little inconsistent and vary by up to +/- 25 simply by repeating the test. The numbers below reflect the most consistent results. (VFSMark score ranged between 278 and 335 for the Ultra-II.)

VFSMark^ (SD128MB / SD256MB Ultra-II)
- File Create: 180% / 462%
- File Delete: 194% / 293%
- File Write: 47% / 211%
- File Read: 169% / 169%
- File Seek: 421% / 437%
- DB Export: 58% / 212%
- DB Import: 419% / 421%
- Record Access: 329% / 332%
- Resource Access: 325% / 325%
- VFS Mark: 238 / 318 (average)
^... test device: palmOne Treo 600

For comparison purposes I also list the results from my test of the Sandisk MemoryStick Pro. Please note that different hardware may skew results and differences don't refer to the memory alone. ...

VFSMark* (MS / MSPro)
- File Create: 111% / 313%
- File Delete: 62% / 198%
- File Write: 26% / 23%
- File Read: 146% / 343%
- File Seek: 181% / 240%
- DB Export: 78% / 115%
- DB Import: 236% / 353%
- Record Access: 262% / 320%
- Resource Access: 235% / 300%
- VFS Mark: 148 / 245 (average)
*... test device: Sony Clie PEG-NX60

Interpretation: The SD 256MB Ultra-II is the first card I tested that actually returned a solid writing performance, that's the main component in the higher score over the standard SD card and realisticaly the MemoryStick as well. Impact is mostly visible when the program attempts to write to the memory card.

Similar read speed for the Ultra as seen for the standard model suggests that the Treo 600 interface is pretty much maxed out with this test and faster memory may not gain improvements. (Read speed of flash memory is usually much higher than the write speed anyway.)

I am not sure why the Memory Stick performed relatively poorly and for now would 'blame' the NX60 since its hardware is not optimized for the Pro format. Another reason could be that VFSMark was developed on a Palm m500 and may put the Sony at a disadvantage.

Real life applications: Backups are greatly impacted by the media speed and as it can be seen in the comparison below, the Ultra-II sure does improve performance. (Slightly better than the VFSMark score suggests.)

Backup size = 10MB
Backup Files = 148
Test Device = Treo 600

Full Backup to SD (SD128MB / SD256MB Ultra-II)
- FlyBackup v1.7: 52 sec. / 36 sec.
- TealBackup v1.01: 104 sec. / 68 sec.

Running FlyBackup on the NX60 revealed that the supposed low write performance of the MemoryStick Pro seems to be real, since a full backup took 58 seconds for 8MB. I am not exactly sure why.


SECURE DIGITAL MEDIA

Besides the flash memory chip, all SD cards follow the same standard and share similar features ...

Lock Switch: Similar to Sony's memory stick, the SD media provides a mechanical switch that works as a global write protection for the memory card. No data can be added, altered or deleted and that makes it valuable for static content like system backups. The switch is relatively hidden and only a tiny word ('lock') gives the locking position away.

Transfer: The variable clock rate of up to 25MHz is part of the reason for the maximum read and write speed. SD cards defined by the 1.01 specs (April 2001) theoretically achieve up to 10MByte/sec of data transfer from and to the card. Hence, the Ultra-II is pretty much the fastest SD there can be.

Copyright protection: Unlike Memory Stick and Compact Flash, SD cards are by default encrypted and allow storage of copyrighted material. SD cards use 'Content Protection for Recordable Media' (CPRM) similar to DVDs. The only difference is the "key revocation" technology that is built into SD cards. Sony's MagicGate is the solution for memory stick media does the same, but I am not aware of such mechanism for CF cards.

Thick or Thin: Normal SD cards are 2.1 mm thick and the SanDisk SD256MB falls into that category. The standard allows for a slightly thinner version with 1.4 mm.

Capacity: There is no specific limit in the specification for a maximum memory size, but up to 8GB are under development and given most applications that sure will be enough for a few years. (8GB are not going to be cheap for a while anyway.)

Full SD specifications ...
http://www.sdcard.org/sdio/Simplified%20Physical%20Layer%20Specification.PDF

Recommended: Yes