I have a Memorex Universal card reader that I use mostly for Compact Flash cards for my camera. I also use it on a 128 MB SanDisk SD card I have been using in my Treo600. I just purchased a Lexar JumpDrive trio (a USB device like a flash drive but it holds SD cards) and a Lexar 256 MB SD card, primarily to move files between computers.

The Lexar drive and Lexar card work fine together; the Lexar and SanDisk cards work fine in the Treo600, and the SanDisk card works fine in both the Lexar drive and the Memorex reader. However, the Lexar 256 MB card is not recognized by the Memorex reader. Basically, I can show that the Memorex reader works (with a SanDisk card) and that the Lexar card works (with a Lexar drive and with the Treo600), but they don't work together.

A Memorex rep suggested that Lexar cards must be incompatible with their reader. She said I should return the card and stick with SanDisk cards, because they work.

On the other hand, the first Lexar rep (chat line) said theirs are "industry standard cards" that should be compatible with any reader that can read a 256 MB card. He gave me a phone number for a senior tech rep.

That Lexar rep said that there are four ways that SD cards are made, even though they may look the same on the outside. Mine is marked "Made in USA" which means it is a different design than their cards made in Japan. He said the Japanese-made cards are the same printed circuit design as the SanDisk cards, so one of those should work fine for me. He said he would send me one in exchange for my returning the one I have -- gave me an RMA number and an address.

Do we really need to worry about differences in internal designs of SD cards, with some working in a device and others not? How would you know what card to buy in a store? Apparently, it is not just a matter of choosing the right brand. Anyone have any suggestions/comments on this topic? All of this was news to me.