To dig a little deeper here, let’s take a quick look at an actual device: an IDE disk driver“AT Attachment Interface for Disk Drives” by Lawrence J. Lamers. Reference number: ANSI X3.221, 1994. Available: ftp://ftp.t10.org/t13/project/d0791r4c-ATA-1.pdf. A rather dry document about device interfaces. Read it at your own peril.. We summarize the protocol as described in this reference“Hard Disk Driver” by Washington State Course Homepage. Available online at this site: http://eecs.wsu.edu/ ̃cs460/cs560/HDdriver.html. A nice summary of a simple IDE disk drive’s interface and how to build a device driver for it.; we’ll also peek at the xv6 source code“The xv6 Operating System” by Russ Cox, Frans Kaashoek, Robert Morris, Nickolai Zeldovich. From: http://pdos.csail.mit.edu/6.828/2008/index.html. See ide.c for the IDE device driver, with a few more details therein. for a simple example of a working IDE driver.