Hardware Documentation - Busses - ATA/ATAPI

Here are some links to information about the AT Attachment bus, an evolution of EISA/IDE.

The AT Attachment Technical Committee. Many drafts, specs, and proposals.

Primarily describes the Mac OS ADB Manager, but also how to communicate with devices on the ADB at a very low level.
IDE - Hardware Reference

Pin assignments, register descriptions, I/O ports...
EIDE storage page

Peter den Haan's pages on Enhanced IDE (ATA-2).