SanDisk 4GB Micro SDHC memory card
Tiny form-factor, big storage capacity
Review Micro SD memory cards are tiny - less than a ¼ of the size of a regular SD card and ½ as thick - but to date, their storage capacity has remained fairly small too. The SDHC - SD High Capacity - specification is about to change that, as it has with regular SD cards...and Register Hardware this week received one of the first Micro SDHC cards: a 4GB sliver from SanDisk.
SanDisk's 4GB Micro SD card: NOT actual size...
SDHC boosts card capacity by allowing cards of greater capacity than 2GB, starting at 4GB. Regular SD cards use the FAT16 file system, but SDHC uses FAT32 to boost the range of memory addresses it can access and so store. Micro SD versions work the same way.
The snag: you need a compatible device to use a higher capacity card, and right now few do. Nokia's N95 mulitmedia phone - reviewed here  - is one, and when we tried the two together, the phone easily recognised the SanDisk Micro SDHC card's full capacity. Other, non-SDHC aware devices just ignored it.
SanDisk's 4GB Micro SD card: still not actual size...
SanDisk's Micro SDHC is rated a Class 2 device - not that you'll see this mentioned on the card itself, as SanDisk isn't keen in this rating  - which means its capable of a minimum guaranteed data transfer rate of 2MBps. The SDHC spec also includes Class 4 and Class 6 - respectively delivering at least 4MBps and 6MBps.
SanDisk's 4GB Micro SD card: approximately actual size
SanDisk supplied the card with an SD-sized adaptor, so we were able to slot it into a USB 2.0 card reader and copy over some files - a hundred 10MB documents in a folder - copying it first to the drive, then duplicating the folder, then reading it back. Incidentally, retail units will also come with a USB adaptor.
Testing yielded average write, copy and read data transfer speeds of 4.46MBps, 3.21MBps and 8.87MBps, respectively. As you can see from the chart, that compares well with the 4GB SanDisk SDHC card I tried out  back in December 2006. Both cards were tested in the same USB 2.0 port on a MacBook Pro, connected through the same SanDisk MicroMate SDHC-compatible card reader. SanDisk's 512MB Ultra II SD card still has the edge on write speed.
Memory card test results
Speed ratings in MBps - longer bars are better
Of course, you can now get 2GB Ultra II SD cards, and 4GB Extreme III SDHCs if you want the highest SD card speeds and capacities. But then the Micro SDHC card isn't really an alternative to these. While you might use SD cards as an alternative to USB Flash drives, you're probably not going to want to do so with the Micro SDHC - if you're going to be using it in an SD-sized sleeve, whether with a USB adaptor or not, you may as well just buy an SD card and have done with it.
SanDisk's 4GB Micro SD card and adaptor
No, the Micro SDHC is best left to the handsets it was designed for, and as we mentioned that's a very limited number right now. If you're a Nokia N95 owner, the SanDisk card is the best, if not the only way to expand you're handset's storage capacity. More devices will come, so the 4GB card is going to find more homes in future.
SanDisk's 4GB Micro SDHC card isn't going to replace your favourite USB Flash drive, but it's arrival is very good news for owners of the few devices that support the Micro SDHC specification. The card offers plenty of storage at a reasonable price.