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1/ I don't know how flash memory works, so I thought I'd post this picture resulting from searching on Amazon.com for "SanDisk Extreme 64GB". Three different cards named "Extreme", the only difference being "A2"/'A1"/"". My question is why the prices don't match. 
2/ Historically, microSD has been optimized for sequential transfers, but not for random input/output operations (IOPS) that computer application need. Thus, performance for things like Raspberry Pi's has been poor.
3/ The new "Application" A1/A2 rating on these cards is now designed to guarantee a minimal number of IOPS, because mobile phones need this now, as well as Raspberry Pi type devices.
4/ The U3 icon the device means "minimum 30-megabytes-per-second" for photos. Cards can peek at 150-megabytes easily, but peeks are dishonest ratings. That's why there are U1 (10MBps) and U3 (30MBps) ratings to guarantee a minimum speed.
5/ But apparently video has different issues, so they now have a separate rating of V30 for 30-megabytes-per-second for video recording. It's a different speed than U3, and I don't understand what technically is different. I assume it restricts the occasional pauses that happen.
6/ I also understand that there is no such thing as a specific model of microSD flash, that the manufacturer can change flash chips, change firmware, or even change controller, from one batch of chips to the next.
7/ What I don't understand is how as the chips have gotten better, they've gone down in price. Is this simply that there are still older batches hanging around that cost more to produce, but price has gone down for newer batches?
