I bought a Pentax k100d DSLR and a 4GB SDHC card.Initially the card would not work in the camera or in my card reader. Fortunately Pentax has a firmware fix for the problem but I had to buy an SDHC card reader for my desktop. Below is a quote from Wikipedia. There is a great explanation of SD & SDHC cards at this site. See en.wikipedia.org/wiki/Secure_Digital_card#SD_and_SDHC_compatibility_issues"As of early 2007, the simultaneous availability of non-standard 4GB SD and 4GB SDHC cards, and incompatibilities between SD and SDHC have caused confusion among various consumers looking to buy memory devices.The following compatibility issues between SD and SDHC cards and devices can arise:* Devices that do not specifically support SDHC do not recognize SDHC memory cards.* Some manufacturers have produced 4GB SD cards that conform to neither the SD2.0/SDHC spec nor existing SD device"