Peter:
Do you already have the hard drive attached and operating with your 8051 and functioning to the level that you are able to read and write individual sectors?

There is info on the WEB and on this forum, via the search function, about interfacing IDE peripherals to an 8051 processor. Some of those posts have links you can go to as well. When you are looking for information do not hesitate to also study the projects that people have done regarding the attachment of CDROM drives to an 8051. These also use the IDE interface and the low level details will be almost identical to the IDE hard drive.

When you search for info on the IDE command set one of the keywords to include in the search string should be ATA. The full ATA specification is not generally available for free as it is a controlled release document and that control is handled by having people purchase the document. However it is often possible to get free copies of the newer versions that are still not officially released by the standardization committee and have been posted for public comment and review. I have previously obtained copies of the ATA document from the Western Digital WEB site. (Note that ATA specs cover IDE topics, SCSI topics, PCMCIA interface topics, Compact Flash Card topics and now serial interface topics).

Michael Karas