The D90 is SDHC compliant and according to this Wiki http://en.wikipedia.org/wiki/SDHC_Card#SDHC
the following rules apply when using SDXC in an SDHC reader
Compatibility with SDHC
SDXC host devices accept all previous families of SD memory cards. Conversely, SDHC host devices will accept SDXC cards that follow Version 3.0, since the interface is identical, but the following issues may affect usability:
SDXC cards are pre-formatted with Microsoft's proprietary and patented exFAT file system, which the host device might not support. Since Microsoft does not publish the specifications of exFAT and its use requires a non-free license, many alternative or older operating systems do not support exFAT for technical or legal reasons. The use of exFAT on some SDXC cards may render SDXC unsuitable as a universal exchange medium, as an SDXC card that uses exFAT would not be usable in all host devices. Since the FAT32 file system supports volumes up to the SDXC's maximum theoretical capacity of 2 TB as well, a user could reformat an SDXC card to use FAT32 for greater portability between computers (see below). FAT32-formatted SDXC cards can be used in a host device built for SDHC if the host device can handle 64GB and larger volumes.
SDHC host devices will not test the new capability bits defined for SDXC 4.0 cards. It will therefore not be able to use the new features of SDXC, such as transfer speeds above UHS104 (104MB/s).
The SD Card org site says this https://www.sdcard.org/consumers/faq/#sdxc_compat
Existing SD devices and SDHC devices are not be compatible with new SDXC memory cards, but existing SD memory cards and SDHC memory cards will still continue to be offered by card manufacturers for the foreseeable future. Existing SD memory cards and SDHC memory cards will work in SDXC devices.
And there is this web page as well http://mansurovs.com/nikon-d90-sdxc-compatibility
The bad news, is that the Nikon D90 currently does not support the SDXC memory. Since the physical interface between SDHC and SDXC cards is the same, Nikon might be able to support SDXC in D90 by releasing a firmware update that can read the SD 3.0 specification. However, based on the history (specifically, the Nikon D50 + SDHC compatibility problem), Nikon probably will not address this problem and only provide support for the SDXC format on the upcoming Nikon D90 update that will be released next year.
So it seems no one can agree on what support you will get. it would seem that sticking with SD and SDHC is your best bet at the moment.
Nikkor AF-S DX; 18-105 f/3.5-5.6G VR, 55-300 f/4.5-5.6G VR, 35mm f/1.8G
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