Today's compact hard drives have custom interfaces. Integrated drive electronics (IDE) and other such interfaces simply have too many pins to be practical. As for serial ATA, it's too new and a bit costly in terms of power and hardware.
The up-and-coming alternative, CE-ATA, is under development by companies from the CE-ATA Work Group. These companies include Intel, Hitachi Global Storage Technologies, Marvell Semiconductor Inc., Seagate Technology, and Toshiba America Information Systems, as well as the MultiMedia Card Association (MMCA).
CE-ATA uses the same electrical interface as the MultiMedia Card (MMC), with modifications to handle a functional subset of the Advanced Technology Attachment (ATA) command set. This permits existing microprocessors with MMC interfaces to readily handle CE-ATA devices, though they will require a new CE-ATA device driver. In the future, microprocessors may have two MMC interfaces, with each supporting only one device.
The CE-ATA 1.0 specification will be finalized soon. Initial products are likely to arrive in 2005.