Recently I bought a new camera (Canon Rebel Xsi--Very happy. Thanks for asking) and found myself with a dilemma. Though I'd spent the last few years shoving CompactFlash cards in my old camera, this new one only uses SD cards. Considering one click of the shutter produces both a RAW and JPEG file which combined take up nearly 20 Mb, I needed sizable cards.

I went online, shopped by price and found myself with 2-8Gb SDHC cards. Right now SDHC memory cards are reasonably cheap. Each card ran under $30. If you shop by a manufacturer's reputation, you're going to pay more--and I suppose important photos or video are worth the extra bucks. I'm just generally cheap.

New camera in hand I took some test shots, popped the SDHC card out, threw it in my reader and... and... and... nothing. "Oh crap," I said to myself. But there was nothing wrong. Everything was working as designed. And of course, that's the problem. SD and SDHC memory cards are not totally compatible! Stick with me. I promise you'll understand.

SD cards come in three physical sizes, tiny, tinier and tiniest. The standard cards, about half the size of a CompactFlash card, are 24 x 32 x 2.1mm. Mini SD cards are 21.5 x 20 x 1.4 mm. Micro SD cards are 15 x11 x 1 mm. Originally these cards were designed to hold a maximum of 2 Gb. Oh designers, what were you thinking? I can burn 2 Gb of photos on my way to the plane to go on vacation!

Enter the newer SDHC standard from the SD Card Association. To increase capacity above 2 Gb the file system was changed from FAT16 to FAT32. Unfortunately, older card readers are stuck on the original system. Put an SDHC card in an old-style standard reader and it might as well be speaking Yiddish.

Here's where we stand:

SD cards can be read in any SD or SDHC reader.
SDHC cards can only be read in SDHC compatible readers.

This means you've got to be careful if you want to upgrade your camera's memory. Is the camera, which doubles as a card reader/writer, capable of addressing that extra space? Is it SDHC compatible?

By the way, you not only get additional capacity with the SDHC cards you also get faster speeds. SDHC cards are marked with what looks like the letter "C" with a number inside. Class 2, 4 and 6 equate to 2, 4 and 6 Mb/second minimum sustained write speed. That's why these cards are good-to-go for most current video applications.

The original internal reader in my PC is now useless. For less than $10 I picked up a pocket size USB 2.0 reader to get back in business. My guess is, I'll be changing PCs before they change the standard again.