I am going to buy a new MicroSD card for my Motorola Milestone. The phone has Cyanogenmod 7. The upper limit as told by the manufacturer is 32GB, and because they got cheaper now, I'm going to buy the maximum possible. However, there are those new types of cards called “Ultra High Speed” which, I believe, weren't available when the phone came out.
Questions: Will those cards work with my device? Do they need any special support from the OS? Will I benefit from extra speed?
Your phone comes with a microSDHC form factor, and according to Scandisk, their cards are compatible:
SanDisk Ultra® microSDXC™ UHS-I card: see specifications tab
Available capacities: 8GB,16GB, 32GB, 64GB
Performance/speed: Up to 30MB/s read speed; write speed lower
Compatibility: Compatible with all microSDHC [or microSDXC ]supporting host devices
SanDisk Extreme Pro® microSDHC™ UHS-I card: see specifications tab
Available capacities: 8GB,16GB
Performance/speed: Up to 95 MB/s (633X) read speed; write speed up to 90 MB/s (600X)
Compatibility: Compatible with all microSDHC supporting host devices
Since the form factor remains the same, there's no problem here.
Your device, while capable of reading, will be unable to take advantages over this new card speeds.
Mainly because this technology is new and the OS simple wasn't prepared for it.
On a personal note: Don't spend your money with this card on that specific phone. You'll have no gain from it.
Will those cards work with my device?
Yes, I believe SDHC UHS-I (Ultra High Speed) cards are backwards compatible and will "work" in an SDHC only device (that the Motorola Milestone appears to be).
Do they need any special support from the OS?
Yes, in order to operate at the advertised higher speeds. "Use of UHS requires that the host device command the card to drop from 3.3-volt to 1.8-volt operation and select the 4-bit transfer mode." Wikipedia - Secure Digital
Will I benefit from extra speed?
No, it will work like an ordinary SDHC Class 10 card.
